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Java About the Tutorial Java is a high-level programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms such as Windows Mac OS and the various versions of UNIX. This tutorial gives a complete understanding of Java. This reference will take you through simple and practical approaches while learning Java Programming language. Audience This tutorial has been prepared for the beginners to help them understand the basic to advanced concepts related to Java Programming language. Prerequisites Before you start practicing various types of examples given in this reference we assume that you are already aware about computer programs and computer programming languages. Execute Java Online For most of the examples given in this tutorial you will find a ‘Try it ’ option which you can use to execute your Java programs at the spot and enjoy your learning. Try following the example using the ‘Try it ’ option available at the top right corner of the following sample code box − public class MyFirstJavaProgram public static void mainString args System.out.println"Hello World" i

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Java Table of Contents About the Tutorial ...................................................................................................................... i Audience .................................................................................................................................. i Prerequisites ............................................................................................................................. i Execute Java Online .................................................................................................................... i Table of Contents ...................................................................................................................... ii JAVA – BASICS ............................................................................................................................1 1. Java – Overview ......................................................................................................................... 2 History of Java .......................................................................................................................... 3 Tools You Will Need .................................................................................................................. 3 Try It Option ............................................................................................................................ 4 What is Next ........................................................................................................................... 4 2. Java - Environment Setup ............................................................................................................ 5 Try it Option Online ................................................................................................................... 5 Local Environment Setup ............................................................................................................ 5 Popular Java Editors .................................................................................................................. 6 What is Next ........................................................................................................................... 6 3. Java – Basic Syntax ..................................................................................................................... 7 First Java Program ..................................................................................................................... 7 Basic Syntax ............................................................................................................................. 8 Java Identifiers ......................................................................................................................... 9 Java Modifiers .......................................................................................................................... 9 Java Variables........................................................................................................................... 9 Java Arrays .............................................................................................................................. 9 Java Enums ............................................................................................................................ 10 Java Keywords ........................................................................................................................ 10 Comments in Java ................................................................................................................... 11 Using Blank Lines .................................................................................................................... 12 Inheritance ............................................................................................................................ 12 Interfaces .............................................................................................................................. 12 What is Next ......................................................................................................................... 12 4. Java – Objects Classes ............................................................................................................ 13 Objects in Java ....................................................................................................................... 13 Classes in Java ........................................................................................................................ 14 Constructors .......................................................................................................................... 14 How to Use Singleton Class ..................................................................................................... 15 Creating an Object .................................................................................................................. 17 Accessing Instance Variables and Methods .................................................................................. 18 Source File Declaration Rules .................................................................................................... 20 Java Package .......................................................................................................................... 20 Import Statements .................................................................................................................. 21 A Simple Case Study ................................................................................................................ 21 What is Next ......................................................................................................................... 23 ii

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Java 5. Java – Basic Datatypes .............................................................................................................. 24 Primitive Datatypes ................................................................................................................. 24 Reference Datatypes ............................................................................................................... 26 Java Literals ........................................................................................................................... 26 What is Next ......................................................................................................................... 28 6. Java – Variable Types ................................................................................................................ 29 Local Variables ....................................................................................................................... 29 Instance Variables ................................................................................................................... 31 Class/static Variables ............................................................................................................... 33 What is Next ......................................................................................................................... 34 7. Java – Modifier Types ............................................................................................................... 35 Java Access Modifiers .............................................................................................................. 35 Java Non-Access Modifiers........................................................................................................ 38 The Static Modifier .................................................................................................................. 38 The Final Modifier ................................................................................................................... 39 The Abstract Modifier .............................................................................................................. 41 Access Control Modifiers .......................................................................................................... 43 Non-Access Modifiers .............................................................................................................. 44 What is Next ......................................................................................................................... 44 8. Java – Basic Operators .............................................................................................................. 45 The Arithmetic Operators ......................................................................................................... 45 The Relational Operators .......................................................................................................... 47 The Bitwise Operators ............................................................................................................. 49 The Logical Operators .............................................................................................................. 52 The Assignment Operators ....................................................................................................... 53 Miscellaneous Operators .......................................................................................................... 57 Precedence of Java Operators ................................................................................................... 59 What is Next ......................................................................................................................... 59 9. Java – Loop Control .................................................................................................................. 60 While Loop in Java .................................................................................................................. 61 for Loop in Java ...................................................................................................................... 62 Do While Loop in Java .............................................................................................................. 65 Loop Control Statements .......................................................................................................... 67 Break Statement in Java ........................................................................................................... 67 Continue Statement in Java ...................................................................................................... 69 Enhanced for loop in Java ......................................................................................................... 70 What is Next ......................................................................................................................... 71 10. Java – Decision Making............................................................................................................. 72 If Statement in Java ................................................................................................................. 73 If-else Statement in Java........................................................................................................... 74 The if . else if .. else Statement ................................................................................................... 76 Nested if Statement in Java ....................................................................................................... 77 Switch Statement in Java .......................................................................................................... 78 The : Operator: .................................................................................................................... 80 What is Next ......................................................................................................................... 81 iii

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Java 11. Java – Numbers Class ............................................................................................................... 82 Number Methods ................................................................................................................... 83 Java XXXValue Method............................................................................................................. 86 Java – compareTo Method ...................................................................................................... 87 Java – equals Method ............................................................................................................ 88 Java – valueOf Method .......................................................................................................... 89 Java – toString Method .......................................................................................................... 91 Java – parseInt Method .......................................................................................................... 92 Java – abs Method ................................................................................................................ 93 Java – ceil Method ................................................................................................................ 94 Java – floor Method .............................................................................................................. 95 Java – rint Method ................................................................................................................ 96 Java – round Method ............................................................................................................. 97 Java – min Method ................................................................................................................ 98 Java – max Method ............................................................................................................... 99 Java – exp Method ...............................................................................................................100 Java – log Method ................................................................................................................101 Java – pow Method ..............................................................................................................102 Java – sqrt Method ...............................................................................................................103 Java – sin Method ................................................................................................................104 Java – cos Method ...............................................................................................................105 Java – tan Method ...............................................................................................................106 Java – asin Method...............................................................................................................107 Java – acos Method ..............................................................................................................108 Java – atan Method ..............................................................................................................109 Java – atan2 Method ............................................................................................................110 Java – toDegrees Method ......................................................................................................111 Java – toRadians Method ......................................................................................................112 Java – random Method .........................................................................................................113 What is Next ........................................................................................................................114 12. Java – Character Class .............................................................................................................115 Escape Sequences ..................................................................................................................115 Character Methods ................................................................................................................117 Java – isLetter Method ..........................................................................................................117 Java – isDigit Method ............................................................................................................118 Java – isWhitespace Method ..................................................................................................119 Java – isUpperCase Method ...................................................................................................120 Java – isLowerCase Method ...................................................................................................121 Java – toUpperCase Method ..................................................................................................122 Java – toLowerCase Method ..................................................................................................123 Java – toString Method .........................................................................................................124 What is Next ........................................................................................................................125 13. Java – Strings Class .................................................................................................................126 Creating Strings .....................................................................................................................126 Java – String Buffer String Builder Classes ................................................................................126 StringBuffer Methods .............................................................................................................127 Java – String Buffer append Method ........................................................................................128 Java – String Buffer reverse Method ........................................................................................129 iv

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Java Java – String Buffer delete Method..........................................................................................130 Java – String Buffer insert Method ..........................................................................................131 Java – String Buffer replace Method ........................................................................................132 String Length .........................................................................................................................135 Concatenating Strings .............................................................................................................136 Creating Format Strings ...........................................................................................................136 String Methods ......................................................................................................................137 Java – String chartAt Method .................................................................................................142 Java – String compareToObject o Method ................................................................................143 Java – String compareToString anotherString Method .................................................................144 Java – String compareToIgnoreCase Method .............................................................................145 Java – String concat Method ..................................................................................................146 Java – String contentEquals Method ........................................................................................147 Java – String copyValueOfchar data Method ...........................................................................148 Java – String copyValueOfchar data int offset int count Method ................................................149 Java – String endsWith Method ..............................................................................................150 Java – String equals Method ..................................................................................................151 Java – String equalsIgnoreCase Method ...................................................................................152 Java – String getBytesString charsetName Method .....................................................................154 Java – String getBytes Method................................................................................................155 Java – String getChars Method ...............................................................................................156 Java – String hashCode Method ..............................................................................................157 Java – String indexOfint ch Method .........................................................................................158 Java – String indexOfint ch int fromIndex Method .....................................................................159 Java – String indexOfString str Method ....................................................................................160 Java – String indexOfString str int fromIndex Method ................................................................161 Java – String Intern Method ...................................................................................................162 Java – String lastIndexOfint ch Method ....................................................................................163 Java – String lastIndexOfint ch int fromIndex Method ................................................................164 Java – String lastIndexOfString str Method ................................................................................165 Java – String lastIndexOfString str int fromIndex Method ............................................................166 Java – String length Method ...................................................................................................167 Java – String matches Method ................................................................................................168 Java – String regionMatches Method .......................................................................................169 Java – String regionMatches Method .......................................................................................171 Java – String replace Method .................................................................................................173 Java – String replaceAll Method ..............................................................................................174 Java – String replaceFirst Method ...........................................................................................175 Java – String split Method ......................................................................................................176 Java – String split Method ......................................................................................................178 Java – String startsWith Method .............................................................................................180 Java – String startsWith Method .............................................................................................181 Java – String subsequence Method..........................................................................................182 Java – String substring Method ...............................................................................................183 Java – String substring Method ...............................................................................................184 Java – String toCharArray Method ...........................................................................................186 Java – String toLowerCase Method ..........................................................................................187 Java – String toLowerCase Method ..........................................................................................188 Java – String toString Method ................................................................................................189 Java – String toUpperCase Method ..........................................................................................189 v

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Java Java – String toUpperCase Method ..........................................................................................190 Java – String trim Method ......................................................................................................191 Java – String valueOf Method .................................................................................................192 14. Java – Arrays .........................................................................................................................196 Declaring Array Variables ........................................................................................................196 Creating Arrays ......................................................................................................................196 Processing Arrays ...................................................................................................................198 The foreach Loops ..................................................................................................................199 Passing Arrays to Methods.......................................................................................................199 Returning an Array from a Method ............................................................................................200 The Arrays Class .....................................................................................................................200 15. Java – Date Time .................................................................................................................202 Getting Current Date Time ....................................................................................................203 Date Comparison ...................................................................................................................204 Simple DateFormat Format Codes .............................................................................................205 Date and Time Conversion Characters ........................................................................................208 Parsing Strings into Dates ........................................................................................................209 Sleeping for a While ...............................................................................................................210 Measuring Elapsed Time .........................................................................................................211 GregorianCalendar Class .........................................................................................................212 16. Java – Regular Expressions .......................................................................................................218 Capturing Groups ...................................................................................................................218 Regular Expression Syntax .......................................................................................................220 Methods of the Matcher Class ..................................................................................................223 17. Java – Methods ......................................................................................................................230 Creating Method ...................................................................................................................230 Method Calling ......................................................................................................................231 The void Keyword ..................................................................................................................232 Passing Parameters by Value ....................................................................................................233 Method Overloading ..............................................................................................................235 Using Command-Line Arguments ..............................................................................................236 The Constructors ...................................................................................................................237 Parameterized Constructor ......................................................................................................238 The this keyword ...................................................................................................................239 Variable Argumentsvar-args ...................................................................................................242 The finalize Method .............................................................................................................243 18. Java – Files and I/O .................................................................................................................244 Stream .................................................................................................................................244 Standard Streams ..................................................................................................................247 Reading and Writing Files ........................................................................................................248 ByteArrayInputStream ............................................................................................................250 DataInputStream ...................................................................................................................253 FileOutputStream ..................................................................................................................255 ByteArrayOutputStream ..........................................................................................................256 DataOutputStream .................................................................................................................259 File Navigation and I/O............................................................................................................261 vi

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Java File Class ..............................................................................................................................262 Directories in Java ..................................................................................................................272 Listing Directories ..................................................................................................................273 19. Java – Exceptions ...................................................................................................................275 Exception Hierarchy ...............................................................................................................276 Built-in Exceptions .................................................................................................................277 Exceptions Methods ...............................................................................................................279 Catching Exceptions ...............................................................................................................280 Multiple Catch Blocks .............................................................................................................281 Catching Multiple Type of Exceptions ........................................................................................282 The Throws/Throw Keywords ...................................................................................................282 The Finally Block ....................................................................................................................283 The try-with-resources ............................................................................................................285 User-defined Exceptions ..........................................................................................................287 Common Exceptions ...............................................................................................................290 20. Java – Inner Classes ................................................................................................................291 Nested Classes ......................................................................................................................291 Inner Classes Non-static Nested Classes ...................................................................................292 Accessing the Private Members ................................................................................................293 Method-local Inner Class .........................................................................................................294 Anonymous Inner Class ...........................................................................................................295 Anonymous Inner Class as Argument .........................................................................................296 Static Nested Class .................................................................................................................297 JAVA - OBJECT ORIENTED.......................................................................................................299 21. Java – Inheritance ...................................................................................................................300 extends Keyword ...................................................................................................................300 Sample Code .........................................................................................................................300 The super keyword .................................................................................................................302 Invoking Superclass Constructor ...............................................................................................305 IS-A Relationship ....................................................................................................................306 The instanceof Keyword ..........................................................................................................308 HAS-A relationship .................................................................................................................309 Types of Inheritance ...............................................................................................................309 22. Java – Overriding ....................................................................................................................311 Rules for Method Overriding ....................................................................................................313 Using the super Keyword .........................................................................................................314 23. Java – Polymorphism ..............................................................................................................315 Virtual Methods.....................................................................................................................316 24. Java – Abstraction ..................................................................................................................320 Abstract Class ........................................................................................................................320 Inheriting the Abstract Class ....................................................................................................323 Abstract Methods ..................................................................................................................324 vii

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Java 25. Java – Encapsulation ...............................................................................................................326 Benefits of Encapsulation ........................................................................................................328 26. Java – Interfaces .....................................................................................................................329 Declaring Interfaces................................................................................................................330 Implementing Interfaces .........................................................................................................330 Extending Interfaces ...............................................................................................................332 Extending Multiple Interfaces ...................................................................................................333 Tagging Interfaces ..................................................................................................................333 27. Java – Packages ......................................................................................................................334 Creating a Package .................................................................................................................334 The import Keyword ...............................................................................................................336 The Directory Structure of Packages ..........................................................................................337 Set CLASSPATH System Variable ...............................................................................................339 JAVA – ADVANCED .................................................................................................................340 28. Java – Data Structures .............................................................................................................341 The Enumeration ...................................................................................................................341 The BitSet .............................................................................................................................343 The Vector ............................................................................................................................348 The Stack ..............................................................................................................................355 The Dictionary .......................................................................................................................358 The Hashtable .......................................................................................................................362 The Properties .......................................................................................................................366 29. Java – Collections Framework ...................................................................................................370 The Collection Interfaces .........................................................................................................371 The Collection Interface ..........................................................................................................372 The List Interface ...................................................................................................................375 The Set Interface ...................................................................................................................378 The SortedSet Interface ..........................................................................................................380 The Map Interface ..................................................................................................................382 The Map.Entry Interface ..........................................................................................................384 The SortedMap Interface .........................................................................................................386 The Enumeration Interface ......................................................................................................388 The Collection Classes .............................................................................................................389 The LinkedList Class ................................................................................................................391 The ArrayList Class .................................................................................................................395 The HashSet Class ..................................................................................................................399 The LinkedHashSet Class .........................................................................................................402 The TreeSet Class ...................................................................................................................403 The HashMap Class ................................................................................................................406 The TreeMap Class .................................................................................................................409 The WeakHashMap Class .........................................................................................................412 The LinkedHashMap Class .......................................................................................................415 The IdentityHashMap Class ......................................................................................................418 The Vector Class ....................................................................................................................422 The Stack Class ......................................................................................................................428 viii

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Java The Dictionary Class ...............................................................................................................430 The Map Interface ..................................................................................................................431 The Hashtable Class ................................................................................................................433 The Properties Class ...............................................................................................................437 The BitSet Class .....................................................................................................................440 The Collection Algorithms ........................................................................................................445 How to Use an Iterator .........................................................................................................450 How to Use a Comparator .....................................................................................................454 Summary ..............................................................................................................................456 30. Java – Generics ......................................................................................................................457 Generic Methods ...................................................................................................................457 Bounded Type Parameters .......................................................................................................459 Generic Classes ......................................................................................................................460 31. Java – Serialization .................................................................................................................462 Serializing an Object ...............................................................................................................463 Deserializing an Object ............................................................................................................464 32. Java – Networking ..................................................................................................................466 URL Processing ......................................................................................................................466 URL Class Methods .................................................................................................................467 URLConnections Class Methods ................................................................................................470 Socket Programming ..............................................................................................................473 ServerSocket Class Methods ....................................................................................................474 Socket Class Methods .............................................................................................................475 InetAddress Class Methods ......................................................................................................477 Socket Client Example .............................................................................................................477 Socket Server Example ............................................................................................................479 33. Java – Sending E-mail ..............................................................................................................481 Send a Simple E-mail ..............................................................................................................481 Send an HTML E-mail ..............................................................................................................483 Send Attachment in E-mail.......................................................................................................485 User Authentication Part .........................................................................................................487 34. Java – Multithreading .............................................................................................................488 Life Cycle of a Thread ..............................................................................................................488 Thread Priorities ....................................................................................................................489 Create a Thread by Implementing a Runnable Interface ................................................................489 Create a Thread by Extending a Thread Class ...............................................................................491 Thread Methods ....................................................................................................................494 Major Java Multithreading Concepts .........................................................................................499 Thread Synchronization...........................................................................................................499 Interthread Communication .....................................................................................................504 Thread Deadlock ....................................................................................................................507 Thread Control ......................................................................................................................510 35. Java – Applet Basics ................................................................................................................515 Life Cycle of an Applet ............................................................................................................515 A "Hello World" Applet ..........................................................................................................516 ix

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Java The Applet Class ....................................................................................................................516 Invoking an Applet .................................................................................................................517 HTML applet Tag ................................................................................................................517 HTML Attribute Reference .......................................................................................................519 HTML Events Reference ..........................................................................................................521 Getting Applet Parameters ......................................................................................................526 Specifying Applet Parameters ...................................................................................................527 Application Conversion to Applets .............................................................................................527 Event Handling ......................................................................................................................528 Displaying Images ..................................................................................................................530 Playing Audio ........................................................................................................................532 36. Java – Documentation Comments .............................................................................................534 What is Javadoc ...................................................................................................................534 The javadoc Tags ...................................................................................................................535 x

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Java – Basics

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1. Java – Overview Java programming language was originally developed by Sun Microsystems which was initiated by James Gosling and released in 1995 as core component of Sun Microsystems Java platform Java 1.0 J2SE. The latest release of the Java Standard Edition is Java SE 8. With the advancement of Java and its widespread popularity multiple configurations were built to suit various types of platforms. For example: J2EE for Enterprise Applications J2ME for Mobile Applications. The new J2 versions were renamed as Java SE Java EE and Java ME respectively. Java is guaranteed to be Write Once Run Anywhere. Java is: Object Oriented: In Java everything is an Object. Java can be easily extended since it is based on the Object model. Platform Independent: Unlike many other programming languages including C and C++ when Java is compiled it is not compiled into platform specific machine rather into platform independent byte code. This byte code is distributed over the web and interpreted by the Virtual Machine JVM on whichever platform it is being run on. Simple: Java is designed to be easy to learn. If you understand the basic concept of OOP Java it would be easy to master. Secure: With Javas secure feature it enables to develop virus-free tamper-free systems. Authentication techniques are based on public-key encryption. Architecture-neutral: Java compiler generates an architecture-neutral object file format which makes the compiled code executable on many processors with the presence of Java runtime system. Portable: Being architecture-neutral and having no implementation dependent aspects of the specification makes Java portable. Compiler in Java is written in ANSI C with a clean portability boundary which is a POSIX subset. Robust: Java makes an effort to eliminate error prone situations by emphasizing mainly on compile time error checking and runtime checking. Multithreaded: With Javas multithreaded feature it is possible to write programs that can perform many tasks simultaneously. This design feature allows the developers to construct interactive applications that can run smoothly. Interpreted: Java byte code is translated on the fly to native machine instructions and is not stored anywhere. The development process is more rapid and analytical since the linking is an incremental and light-weight process. High Performance: With the use of Just-In-Time compilers Java enables high performance. 2

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Java Distributed: Java is designed for the distributed environment of the internet. Dynamic: Java is considered to be more dynamic than C or C++ since it is designed to adapt to an evolving environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve accesses to objects on run-time. History of Java James Gosling initiated Java language project in June 1991 for use in one of his many set-top box projects. The language initially called ‘Oak ’ after an oak tree that stood outside Goslings office also went by the name ‘Green ’ and ended up later being renamed as Java from a list of random words. Sun released the first public implementation as Java 1.0 in 1995. It promised Write Once Run Anywhere WORA providing no-cost run-times on popular platforms. On 13 November 2006 Sun released much of Java as free and open source software under the terms of the GNU General Public License GPL. On 8 May 2007 Sun finished the process making all of Javas core code free and open- source aside from a small portion of code to which Sun did not hold the copyright. Tools You Will Need For performing the examples discussed in this tutorial you will need a Pentium 200-MHz computer with a minimum of 64 MB of RAM 128 MB of RAM recommended. You will also need the following softwares: Linux 7.1 or Windows xp/7/8 operating system Java JDK 8 Microsoft Notepad or any other text editor This tutorial will provide the necessary skills to create GUI networking and web applications using Java. 3

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Java Try It Option We have provided you with an option to compile and execute available code online. Just click the Try it button avaiable at the top-right corner of the code window to compile and execute the available code. There are certain examples which cannot be executed online so we have skipped those examples. public class MyFirstJavaProgram public static void mainString args System.out.println"Hello World" There may be a case that you do not see the result of the compiled/executed code. In such case you can re-try to compile and execute the code using execute button available in the compilation pop-up window. What is Next The next chapter will guide you to how you can obtain Java and its documentation. Finally it instructs you on how to install Java and prepare an environment to develop Java applications. 4

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2. Java - Environment Setup In this chapter we will discuss on the different aspects of setting up a congenial environment for Java. Try it Option Online You really do not need to set up your own environment to start learning Java programming language. Reason is very simple we already have Java Programming environment setup online so that you can compile and execute all the available examples online at the same time when you are doing your theory work. This gives you confidence in what you are reading and to check the result with different options. Feel free to modify any example and execute it online. Try the following example using Try it option available at the top right corner of the following sample code box: public class MyFirstJavaProgram public static void mainString args System.out.println"Hello World" For most of the examples given in this tutorial you will find the Try it option which you can use to execute your programs and enjoy your learning. Local Environment Setup If you are still willing to set up your environment for Java programming language then this section guides you on how to download and set up Java on your machine. Following are the steps to set up the environment. Java SE is freely available from the link Download Java. You can download a version based on your operating system. Follow the instructions to download Java and run the .exe to install Java on your machine. Once you installed Java on your machine you will need to set environment variables to point to correct installation directories: Setting Up the Path for Windows Assuming you have installed Java in c:\Program Files\java\jdk directory: Right-click on My Computer and select Properties. Click the Environment variables button under the Advanced tab. 5

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Java Now alter the Path variable so that it also contains the path to the Java executable. Example if the path is currently set to C:\WINDOWS\SYSTEM32 then change your path to read C:\WINDOWS\SYSTEM32c:\Program Files\java\jdk\bin. Setting Up the Path for Linux UNIX Solaris FreeBSD Environment variable PATH should be set to point to where the Java binaries have been installed. Refer to your shell documentation if you have trouble doing this. Example if you use bash as your shell then you would add the following line to the end of your .bashrc: export PATH/path/to/java:PATH Popular Java Editors To write your Java programs you will need a text editor. There are even more sophisticated IDEs available in the market. But for now you can consider one of the following: Notepad: On Windows machine you can use any simple text editor like Notepad Recommended for this tutorial TextPad. Netbeans: A Java IDE that is open-source and free which can be downloaded from http://www.netbeans.org/index.html. Eclipse: A Java IDE developed by the eclipse open-source community and can be downloaded from http://www.eclipse.org/. What is Next Next chapter will teach you how to write and run your first Java program and some of the important basic syntaxes in Java needed for developing applications. 6

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3. Java – Basic Syntax When we consider a Java program it can be defined as a collection of objects that communicate via invoking each others methods. Let us now briefly look into what do class object methods and instance variables mean. Object - Objects have states and behaviors. Example: A dog has states - color name breed as well as behavior such as wagging their tail barking eating. An object is an instance of a class. Class - A class can be defined as a template/blueprint that describes the behavior/state that the object of its type supports. Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written data is manipulated and all the actions are executed. Instance Variables - Each object has its unique set of instance variables. An objects state is created by the values assigned to these instance variables. First Java Program Let us look at a simple code that will print the words Hello World. public class MyFirstJavaProgram / This is my first java program. This will print Hello World as the output / public static void mainString args System.out.println"Hello World" // prints Hello World Lets look at how to save the file compile and run the program. Please follow the subsequent steps: Open notepad and add the code as above. Save the file as: MyFirstJavaProgram.java. Open a command prompt window and go to the directory where you saved the class. Assume its C:\. 7

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Java Type javac MyFirstJavaProgram.java and press enter to compile your code. If there are no errors in your code the command prompt will take you to the next line Assumption : The path variable is set. Now type java MyFirstJavaProgram to run your program. You will be able to see Hello World printed on the window. C:\ javac MyFirstJavaProgram.java C:\ java MyFirstJavaProgram Hello World Basic Syntax About Java programs it is very important to keep in mind the following points. Case Sensitivity - Java is case sensitive which means identifier Helloand hello would have different meaning in Java. Class Names - For all class names the first letter should be in Upper Case. If several words are used to form a name of the class each inner words first letter should be in Upper Case. Example: class MyFirstJavaClass Method Names - All method names should start with a Lower Case letter. If several words are used to form the name of the method then each inner words first letter should be in Upper Case. Example: public void myMethodName Program File Name - Name of the program file should exactly match the class name. When saving the file you should save it using the class name Remember Java is case sensitive and append .java to the end of the name if the file name and the class name do not match your program will not compile. Example: Assume MyFirstJavaProgram is the class name. Then the file should be saved as MyFirstJavaProgram.java public static void mainString args - Java program processing starts from the main method which is a mandatory part of every Java program. 8

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Java Java Identifiers All Java components require names. Names used for classes variables and methods are called identifiers. In Java there are several points to remember about identifiers. They are as follows: All identifiers should begin with a letter A to Z or a to z currency character or an underscore _. After the first character identifiers can have any combination of characters. A key word cannot be used as an identifier. Most importantly identifiers are case sensitive. Examples of legal identifiers: age salary _value __1_value. Examples of illegal identifiers: 123abc -salary. Java Modifiers Like other languages it is possible to modify classes methods etc. by using modifiers. There are two categories of modifiers: Access Modifiers: default public protected private Non-access Modifiers: final abstract strictfp We will be looking into more details about modifiers in the next section. Java Variables Following are the types of variables in Java: Local Variables Class Variables Static Variables Instance Variables Non-static Variables Java Arrays Arrays are objects that store multiple variables of the same type. However an array itself is an object on the heap. We will look into how to declare construct and initialize in the upcoming chapters. 9

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Java Java Enums Enums were introduced in Java 5.0. Enums restrict a variable to have one of only a few predefined values. The values in this enumerated list are called enums. With the use of enums it is possible to reduce the number of bugs in your code. For example if we consider an application for a fresh juice shop it would be possible to restrict the glass size to small medium and large. This would make sure that it would not allow anyone to order any size other than small medium or large. Example class FreshJuice enum FreshJuiceSize SMALL MEDIUM LARGE FreshJuiceSize size public class FreshJuiceTest public static void mainString args FreshJuice juice new FreshJuice juice.size FreshJuice.FreshJuiceSize.MEDIUM System.out.println"Size: " + juice.size The above example will produce the following result: Size: MEDIUM Note: Enums can be declared as their own or inside a class. Methods variables constructors can be defined inside enums as well. Java Keywords The following list shows the reserved words in Java. These reserved words may not be used as constant or variable or any other identifier names. abstract assert boolean break byte case catch char 10

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Java class const continue default do double else enum extends final finally float for goto if implements import instanceof int interface long native new package private protected public return short static strictfp super switch synchronized this throw throws transient try void volatile while Comments in Java Java supports single-line and multi-line comments very similar to C and C++. All characters available inside any comment are ignored by Java compiler. public class MyFirstJavaProgram / This is my first java program. This will print Hello World as the output This is an example of multi-line comments. / public static void mainString args // This is an example of single line comment / This is also an example of single line comment. / System.out.println"Hello World" 11

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Java Using Blank Lines A line containing only white space possibly with a comment is known as a blank line and Java totally ignores it. Inheritance In Java classes can be derived from classes. Basically if you need to create a new class and here is already a class that has some of the code you require then it is possible to derive your new class from the already existing code. This concept allows you to reuse the fields and methods of the existing class without having to rewrite the code in a new class. In this scenario the existing class is called the superclass and the derived class is called the subclass. Interfaces In Java language an interface can be defined as a contract between objects on how to communicate with each other. Interfaces play a vital role when it comes to the concept of inheritance. An interface defines the methods a deriving class subclass should use. But the implementation of the methods is totally up to the subclass. What is Next The next section explains about Objects and classes in Java programming. At the end of the session you will be able to get a clear picture as to what are objects and what are classes in Java. 12

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4. Java – Objects Classes Java is an Object-Oriented Language. As a language that has the Object-Oriented feature Java supports the following fundamental concepts: Polymorphism Inheritance Encapsulation Abstraction Classes Objects Instance Method Message Parsing In this chapter we will look into the concepts - Classes and Objects. Object - Objects have states and behaviors. Example: A dog has states - color name breed as well as behaviors – wagging the tail barking eating. An object is an instance of a class. Class - A class can be defined as a template/blueprint that describes the behavior/state that the object of its type support. Objects in Java Let us now look deep into what are objects. If we consider the real-world we can find many objects around us cars dogs humans etc. All these objects have a state and a behavior. If we consider a dog then its state is - name breed color and the behavior is - barking wagging the tail running. If you compare the software object with a real-world object they have very similar characteristics. Software objects also have a state and a behavior. A software objects state is stored in fields and behavior is shown via methods. So in software development methods operate on the internal state of an object and the object-to-object communication is done via methods. 13

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Java Classes in Java A class is a blueprint from which individual objects are created. Following is a sample of a class. public class Dog String breed int ageC String color void barking void hungry void sleeping A class can contain any of the following variable types. Local variables: Variables defined inside methods constructors or blocks are called local variables. The variable will be declared and initialized within the method and the variable will be destroyed when the method has completed. Instance variables: Instance variables are variables within a class but outside any method. These variables are initialized when the class is instantiated. Instance variables can be accessed from inside any method constructor or blocks of that particular class. Class variables: Class variables are variables declared within a class outside any method with the static keyword. A class can have any number of methods to access the value of various kinds of methods. In the above example barking hungry and sleeping are methods. Following are some of the important topics that need to be discussed when looking into classes of the Java Language. Constructors When discussing about classes one of the most important sub topic would be constructors. Every class has a constructor. If we do not explicitly write a constructor for a class the Java compiler builds a default constructor for that class. 14

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Java Each time a new object is created at least one constructor will be invoked. The main rule of constructors is that they should have the same name as the class. A class can have more than one constructor. Following is an example of a constructor: public class Puppy public Puppy public PuppyString name // This constructor has one parameter name. Java also supports Singleton Classes where you would be able to create only one instance of a class. Note: We have two different types of constructors. We are going to discuss constructors in detail in the subsequent chapters. How to Use Singleton Class The Singletons purpose is to control object creation limiting the number of objects to only one. Since there is only one Singleton instance any instance fields of a Singleton will occur only once per class just like static fields. Singletons often control access to resources such as database connections or sockets. For example if you have a license for only one connection for your database or your JDBC driver has trouble with multithreading the Singleton makes sure that only one connection is made or that only one thread can access the connection at a time. 15

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Java Implementing Singletons Example 1 The easiest implementation consists of a private constructor and a field to hold its result and a static accessor method with a name like getInstance. The private field can be assigned from within a static initializer block or more simply using an initializer. The getInstance method which must be public then simply returns this instance − // File Name: Singleton.java public class Singleton private static Singleton singleton new Singleton / A private Constructor prevents any other class from instantiating. / private Singleton / Static instance method / public static Singleton getInstance return singleton / Other methods protected by singleton-ness / protected static void demoMethod System.out.println"demoMethod for singleton" Here is the main program file where we will create a singleton object: // File Name: SingletonDemo.java public class SingletonDemo public static void mainString args Singleton tmp Singleton.getInstance tmp.demoMethod 16

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Java This will produce the following result − demoMethod for singleton Example 2 Following implementation shows a classic Singleton design pattern: public class ClassicSingleton private static ClassicSingleton instance null private ClassicSingleton // Exists only to defeat instantiation. public static ClassicSingleton getInstance ifinstance null instance new ClassicSingleton return instance The ClassicSingleton class maintains a static reference to the lone singleton instance and returns that reference from the static getInstance method. Here ClassicSingleton class employs a technique known as lazy instantiation to create the singleton as a result the singleton instance is not created until the getInstance method is called for the first time. This technique ensures that singleton instances are created only when needed. Creating an Object As mentioned previously a class provides the blueprints for objects. So basically an object is created from a class. In Java the new keyword is used to create new objects. There are three steps when creating an object from a class: Declaration: A variable declaration with a variable name with an object type. Instantiation: The new keyword is used to create the object. Initialization: The new keyword is followed by a call to a constructor. This call initializes the new object. 17

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Java Following is an example of creating an object: public class Puppy public PuppyString name // This constructor has one parameter name. System.out.println"Passed Name is :" + name public static void mainString args // Following statement would create an object myPuppy Puppy myPuppy new Puppy "tommy" If we compile and run the above program then it will produce the following result: Passed Name is :tommy Accessing Instance Variables and Methods Instance variables and methods are accessed via created objects. To access an instance variable following is the fully qualified path: / First create an object / ObjectReference new Constructor / Now call a variable as follows / ObjectReference.variableName / Now you can call a class method as follows / ObjectReference.MethodName 18

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Java Example This example explains how to access instance variables and methods of a class. public class Puppy int puppyAge public PuppyString name // This constructor has one parameter name. System.out.println"Name chosen is :" + name public void setAge int age puppyAge age public int getAge System.out.println"Puppys age is :" + puppyAge return puppyAge public static void mainString args / Object creation / Puppy myPuppy new Puppy "tommy" / Call class method to set puppys age / myPuppy.setAge 2 / Call another class method to get puppys age / myPuppy.getAge / You can access instance variable as follows as well / System.out.println"Variable Value :" + myPuppy.puppyAge 19

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Java If we compile and run the above program then it will produce the following result: Name chosen is :tommy Puppys age is :2 Variable Value :2 Source File Declaration Rules As the last part of this section lets now look into the source file declaration rules. These rules are essential when declaring classes import statements and package statements in a source file. There can be only one public class per source file. A source file can have multiple non-public classes. The public class name should be the name of the source file as well which should be appended by .java at the end. For example: the class name is public class Employee then the source file should be as Employee.java. If the class is defined inside a package then the package statement should be the first statement in the source file. If import statements are present then they must be written between the package statement and the class declaration. If there are no package statements then the import statement should be the first line in the source file. Import and package statements will imply to all the classes present in the source file. It is not possible to declare different import and/or package statements to different classes in the source file. Classes have several access levels and there are different types of classes abstract classes final classes etc. We will be explaining about all these in the access modifiers chapter. Apart from the above mentioned types of classes Java also has some special classes called Inner classes and Anonymous classes. 20

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