logging in or signing up java chapter-1 dineshkavitha Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1323 Category: Education License: All Rights Reserved Like it (8) Dislike it (0) Added: July 06, 2010 This Presentation is Public Favorites: 6 Presentation Description No description available. Comments Posting comment... By: ajaysuri (7 month(s) ago) pls send this ppt to my mail id:surekamca.d@gmail.com Saving..... Post Reply Close Saving..... Edit Comment Close By: anandsp1990 (7 month(s) ago) pls send this to my mail anandsp1990@gmail.com Saving..... Post Reply Close Saving..... 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INHERITANCE AND METHOD OVERRIDING 9.1. Super-classes and Subclasses 10. GENERIC METHODS 11. GARBAGE COLLECTION 12. RECURSION 12.1. recursive function 12.2. induction 12.3. recursive methods Slide 4: 13. TESTING AND DUBUGGING 13.1. what is testing 13.2. designing test data 13.3. debugging 1. INTRODUCTION : 1. INTRODUCTION 1.1. HISTORY OF JAVA 1. Java programming language is usually associated with “ World Wide Web ”. 2. Java predates the Web. 3. Java began it’s life as the programming language “ Oak ”. 4. Oak was developed by the “Green Project Members” * Patrick Naughton * Mike Sheridan * James Gosling 5. A group formed in 1991 to create products for the “ Smart electronic Markets “ Slide 6: 6. The existing programming language were not suitable for “ consumer electronics “. 7. The Chief Programmer of Sun Microsystem – James Gosling : created the software for controlling “ Consumer Electronic devices “. 8. The team wanted a fundamentally new way of computing , based on the power of “ Networks “. And the S/W to run on different kinds of computers 9. Patenting issues gave a new name to Oak – Java. 10. HotJava - The first Java-enabled Web browser characteristics of java : characteristics of java Java is simple Java is object-oriented Java is distributed Java is interpreted Java is robust Java is secure Java is architecture-neutral Java is portable Java is high-performance Java is multithreaded Java is dynamic language Slide 8: Java is simple Java is simple language, can be learned easily. Java is object-oriented Java provides Abstraction, Encapsulation, Inheritance and Polymorphism. Java is distributed Java is tuned to the Web, So java program can access data – across the Web as easily as they access data from local system. Java is interpreted Java is both Interpreted and compiled. The code is complied to byte code that’s “ Binary “ and “ platform independent”. Slide 9: Java is robust Java forces the programmer to handle unexpected errors. This ensure that java programs are “Robust” (Reliable) and bug free and don’t crash. Java is secure A program traveling from internet to pc could possibly carry a virus. Java done strong type-checking on the user-machine, and changes in the program are tagged as errors and program will not executed. So, java is “secure”. . Java is architecture-neutral The byte code can be executed on a variety of computers running on different operating systems. Slide 10: Java is portable Java program can run on any machine that has a java interpreter. Other people can use the programs written in java, even if they have different machines with different operating systems. Java is multithreaded perform multiple task at the same time. Java is dynamic language Maintaining different versions of an application is very easy in Java. 2. STRUCTURE OF JAVA PROGRAM : 2. STRUCTURE OF JAVA PROGRAM Types of Java Programs are: 1. Applications (or) stand-alone program - they are program that don’t need a browser to run simultaneously. - need MS-DOS or UNIX prompt to execute the program. 2. Applets - Applets are programs that execute inside a Web page. - Applets require a Java enabled browser like * MS-internet Explorer * Netscape Navigator * Hotjava - Applet have Graphical User Interface. Slide 12: 3. Servlets - these programs extend the functionality of web servers 4. Packages - they are collections of classes that can be shared by other Java programs. 2.1. standard program and Applets : 2.1. standard program and Applets Every java program is a – CLASS Every class may contain data and METHOD members 2.2. packages : 2.2. packages DEFINITION A Package is a collection of classes that can be shared by java program. Packages are used to organize classes into groups. Types of Packages (i). Pre-defined (ii). User-defined 1. java.lang 2. java.util user can 3. java.applet create their 4. java.awt own packages 5. java.io (e.g) lab program 6. java.net Slide 15: 1. java.lang - provides classes and interfaces that are fundamental to java programming. 2. java.util - provides classes that support collections, data and calendar operations, parsing, internationalization and basic event processing. Also refers to all programs in the directory (lang/java or lang\java). 3. java.applet - provides classes, necessary for basic applet programming. 4. java.awt (abstract window toolkit) - provides classes for creating GUI programs. Slide 16: 5. java.io - provides classes for reading and writing data in the form of streams. (input stream, output stream) e.g: memory, file, buffer, network 6. java.net - provides classes that provide network programming. 2.3. importing classes and Packages : 2.3. importing classes and Packages Syntax for package import <package_name>.*; import <package_name> . <class_name>; Example: import java.awt.*; import java.awt.Button; import java.awt.*; in this syntax all the classes in awt package have to imported import java.awt.Button; in this syntax only button class from awt package have to imported 3. The java compiler and virtual machine : 3. The java compiler and virtual machine Java source code is converted into Java Byte code (or) J-code. * When the program <programName> is compiled, the program source code is read from the file <programName.java> * The compiled byte code is written in the file <programName.class> * Java Virtual Machine (JVM) is a software that interpret and executes the byte code. The main task of JVM is – the loading of .class files JVM- has class loaders that loads the .class files, and executed by the execution engine. Slide 19: Each java applications run inside a JVM. JVM starts when you start a java program and terminates when the program ends. The no. of JVM starts when you start a java program and terminates when the program ends. CLASS LOADER ARCHITECTURE 1. A JVM can have many class Loader. They provide security and network to java programs. 2. The JVM has two types of class loaders. (a) Primordial Class Loader (b) Class Loader Objects Slide 20: (a) Primordial Class Loader A primordial Class Loader is a part of the JVM implementation. It loads the java API classes when you execute a java program. (b) Class Loader Objects An application can create many class loaders at runtime for loading the classes of the application. Class Loader Class Loader Java API Primordial Class Loader Java Virtual Machine Implementation Implementation of Class Loader Slide 21: JAVA VIRUTAL MACHINE Slide 22: Through the Java VM, the same application is capable of running on multiple platforms. Slide 23: The Java platform has two components: – The Java Virtual Machine (JVM) – The Java Application Programming Interface (API) 4. DOCUMENTATION comments : 4. DOCUMENTATION comments A comment is a message for a programmer & describes a class, a method, or even a statement. The complier ignore what you write as comments Comments are ignored by the compiler but are useful to other programmers Java support three styles of comments: 1. Multiple line comments 2. Single line comment entries 3. The javadoc comments 1.Multiple line comments Anything you write between /* and */ is treated as a comment. The text that you type here can cover many lines. /* multiple line comments */ Slide 25: 2. Single line comment entries anything you type after // is treated as a comment. The text can’t span (extend) more than a line. If you have multiple lines as comments, you must start every line with //. // single line comment 3. The javadoc comments these lines are used by the javadoc utility to create documentation. These comments are similar o the multiple line comments but start with a /** instead of /* /** this is a javadoc comment*/ 5. DATA TYPES : 5. DATA TYPES The data that’s stored in memory can be of many types. For example: * a person’s age is stored as a numeric value & an address is stored as alphanumeric characteristics. * an address is stored as alphanumeric characters Data types are used to define the operations possible on them and the storage method. * The data types in java are classified as: 1. primitive (or) standard data types 2. Abstract (or) derived data types Slide 27: 1. primitive (or) standard data types 2. Abstract (or) derived data types : 2. Abstract (or) derived data types Abstract data types are based on primitive data types and have more functionality than primitive data types. Example “String” is an abstract data type that can store letters, digits and other characters like /,(), : , ; , $ , # * “String ”provides methods for concatenating two strings, searching for one string within another, and extracting a portion of a string. The primitive data types don’t have these features. 6. METHODS : 6. METHODS 1. parameters A method is a body of code that’s used for performing a set of tasks. The behavior of an object is determined by the program. Declaring Methods: syntax: [<access_specifier>] [<modifiers>] <return_type> <method_name> ([argument_list]) { //statements } Slide 31: Example: public static int abc (int a, int b, int c) { return a+b*c+b/c; } Where: abc - name of the method int - return type of the method is ‘int’ (int a, int b, int c) – formal paramenters of the method abc, each is of integer type. Slide 32: If the method is invoked by the statement Z = abc (2,x,y) then 2,x,y are the ‘actual parameter’. * when the method ‘abc’ is invoked the a - is assigned to 2 b - is assigned to x c - is assigned to y * In java all method parameters are ‘value parameters’. * At run time the value of each ‘actual parameter’ is copied into the corresponding format parameter before the method is executed. 2. Overloaded methods : 2. Overloaded methods Overloading is a technique in which more than one method having the same name can be present in a program. The compiler resolves the method to be invoked using the signature of the method. Function signature 1. The name of the method 2. The number of arguments it takes 3. The data type of the arguments 4. The order of the arguments - when we call a method, the compiler uses the signature of the method to resolve the method to be invoked. - A class can’t have two methods having the same signature. Slide 34: - this is because the compiler will not know which method to invoke if more than one method has the same signature. Example: java supports method overloading and hence, the methods can be declared as follows: * public void add(int a, int b); // add two integers * public void add(float a, float b); // add two floats * public void add(float a, int b); // adds a float and an integer * In the following example the ‘calculator’ class, the methods have the same name but different parameters and the signatures of the methods are different. Slide 35: class calculator { public int add(int a, int b) { System.out.println("int and int"); return a + b; } public float add(float a, float b) { System.out.println("float and float"); return a + b; } Slide 36: public float add(float a, int b) { System.out.println("float and int"); return a + b; } public static void main(String args[]) { calculator c = new calculator(); System.out.println(c.add(1,10)) System.out.println(c.add(1.6f,10.5f)); } } Slide 38: class calculator { public int add(int a, int b) { System.out.println("int and int"); return a + b; } public float add(float a, float b) { System.out.println("float and float"); return a + b; } Slide 39: public float add(float a, int b) { System.out.println("float and int"); return a + b; } public static void main(String args[]) { calculator c = new calculator(); System.out.println(c.add(1,10)) System.out.println(c.add(1.6f,10.5f)); System.out.println(c.add(10.5f,2)); } } 7. EXCEPTIONS : 7. EXCEPTIONS An exception is defined as an ‘abnormal’ event that occurs during program execution and disturb the normal flow of instructions. Error-handling becomes necessary, when developing applications and need to take care of unexpected situations. The unexpected situations that may occur during program execution are: * Running out of memory * Resource allocation errors * Inability to find files * Problems in network connectivity Exception-Handling Techniques : Exception-Handling Techniques When an unexpected error occurs in a method, java creates an object of the types ‘ Exception’. After creating the Exception object, java sends it to the program, by an action called “throwing an exception”. The Exception object contains information about the - type of error - status of the program when the exception occurred * Key words in Excepting: try catch throw throws finally Slide 43: Try Block syntax: try { //statements that may cause an exception } * If an exception occurs within the try block, the appropriate exception-handler that’s associated with the try block handles the exception. * A try block must have at least one catch block that follows it immediately. Slide 44: catch Block syntax: try { //statements that may cause an exception } catch(……) { // error handling routines } The catch statement take the object of the exception class that refers to the exception caught. Once the exception is caught, the statements within the catch block are executed. The scope of the catch block is based on the statement in the preceding try block. Exception handling mechanism : Exception handling mechanism In java, exception-handling facility handles abnormal & unexpected situation in a structured manner. When an exception occurs, the java runtime system searches for an exception-handler (try-catch-block). If a handler is not found in the current method, the handler is searched for in the ‘calling method’. The searches goes on till the runtime system finds an appropriate exception-handler. EXAMPLE: // derivedclass.java class baseclass { public int divide(int num1, int num2) { Slide 46: return num1 / num2; } } public class derivedclass extends baseclass { public int divide(int a, int b) { return super.divide(a,b); } public static void main(String args[]) { int result = 0; derivedclass d1 = new derivedclass(); Slide 47: try { result = d1.divide(100, 0); } catch(ArithmeticException e) { System.out.println(“Error…division by zero”); } System.out.println(“The result is: “ + result”); } } Multiple catch block - example : Multiple catch block - example public class trycatch { public static void main(String args[]) { int num1, num2, result = 0; num1 = 100; num2 = 0; try { result = num1/num2; } Slide 50: catch(ArithmeticException e) { System.out.println("Error---division by zero"); } catch(ArrayIndexOutOfBoundsException e) { System.out.println("Error----out of bounds"); } catch(Exception e) { System.out.println("some other error"); } System.out.println("The result is: " + result); } } Slide 52: EXAMPLE-2 public class trycatch { public static void main(String args[]) { int num1, num2, result = 0; num1 = 100; num2 = 4; try { result = num1/num2; } Slide 53: catch(ArithmeticException e) { System.out.println("Error---division by zero"); } catch(ArrayIndexOutOfBoundsException e) { System.out.println("Error----out of bounds"); } catch(Exception e) { System.out.println("some other error"); } System.out.println("The result is: " + result); } } throw statement : throw statement When a user enters a wrong login-ID (or) password, the throw statement is used to throw an exception. The throw statement takes a single statement, which is an object of the ‘Exception class’. Syntax throw Throwableinstance; * Example throw ThrowObject; The compiler gives an error if the object ‘ThrowObject” doesn’t belong to a valid ‘Exception class’. The ‘throw statement is commonly used in ‘programmer-defined’ exceptions. throws statement : Throws statement is used to specify that ‘ an exception has to be handled by the calling method. It’s used for an exception that a method is capable of raising, but not handling. Syntax [<access_specifier>][<modifier>]<return_type> <method_name> (<arg_list>) [throws <exception_list>] Example public void acceptpassword() throws IllegalAccessException { System.out.println(“ intruder !!”); throw new IllegalAccessException; } throws statement Finally Block : Finally Block The finally block is used when it’s necessary to process certain statements no matter, whether an exception is raised or not. Example try { openFile(); writeFile(); // may cause an exception } catch(……..) { // process the exception } Finally { closeFile(); } Common exceptions : Common exceptions 1. ArithmeticException Exception 2. NullPointerException Exception 3. ArrayIndexOutofBoundsException Exception 8. ACCESS MODIFIERS : 8. ACCESS MODIFIERS An access specifier determines which features of a class (the class itself, the data members, and the method) may be used by the other classes. Java supports three specifiers (or) Access Modifiers 1. public 2. private 3. Protected 4. Default Public access specifier A class, data member (or) method that has a public access specifier can be accessed by any object. An inner class can’t have a public access specifier. Slide 60: Syntax <access_specifier> <return_type> <method> ([argment list]) { ---------- } Example: public class employee { string empname; string empadd; public void displaydetails( ) { // place the code for displaying employee details } } 2. Private access specifier : 2. Private access specifier Only object of the same class can access a variable or a method that has a private access specifier. The variables and method of the inner classes can be declared as private. Example: private int privateVariable; 3. Protected access specifier variable, methods, and inner classes that are declared protected accessible to the subclasses of the class in which they are declared. Example: protected int protectedVariable Slide 62: 4.Default access A class, a variable or a method that doesn’t have an access specifier as private, public, protected is said to have default access. These classes, variables or methods are accessible to all the classes of a package. Example: consider following set of classes y and z inherit from class x. class z belongs to the package p1 and classes x and y belong to the package p2. Class X Class Y Class Z Package p1 Package p2 Slide 63: * A method accesme() has been declared in class X. The following table shows the accessibility of the method accessme() from class Y and Z. MODIFIERS : MODIFIERS Modifiers determine how the data members and methods are used in other classes and objects. The modifiers in java: 1. static 2. final 3. abstract 4. native 5. transient 6. synchronized 7. volatile 9. INHERITANCE AND METHOD OVERRIDING : 9. INHERITANCE AND METHOD OVERRIDING Inheritance is a situation in which a class derives a set of attributes and related behavior from a parent class. 9.1. super classes and subclasses: * super class: super class is a class from which another class inherits properties. It share its properties with its child classes. * sub class: sub class is a class that inherits attributes and methods from a super class. Slide 67: Super class some times referred to as the ‘base class’ and the subclass is referred to as the ‘derived class’. Subclass don’t inherit the constructs of the super class. Example: let us take the example of ‘air tickets’- it can be of two types. Confirmed and request ticket. both the tickets have a lot of common attributes. For example flight_number, date, time and destination. confirmed ticket would have a ‘seat number’, while a request ticket would have a ‘status’. Slide 68: Example: Syntax: public class <subclass name> extends <superclass name> public class confirmedTicket extends Ticket Ticket RequestTicket ConfirmedTicket Final keyword : Final keyword The final modifier doesn’t allow a class to be inherited. A method declared anal can’t be overridden by a subclass. Final- keyword can prevent people from extending a class by using the ‘final’ modifier as follow: example: final class password { -------- } OVERRIDING methods : OVERRIDING methods In overridding, a subcalss method overrrides the definition of a super class method, if the method defined in the subcalss has the same signature of a method in the super class. Example: let us consider the class ‘wheelchair’ is derived from the ‘chair class’. Both the classes have a method called ‘adjustHeight()’. Wheelchair is adjusted differently form the way other chairs are adjusted. Therefore, the wheelchair class overrides superclass method ‘adjustHeight()’. Slide 71: // declaring base class chair (saved as wheelchair.java) class chair { public void adjustHeight() { System.out.println(“adjusting chair height”); } } //deriving wheelchair class from chair public class wheelchair extends chair { public static void main (String args[]) { wheelchair w w = new wheelchair(); w.adjustHeight(); } } Slide 73: // declaring base class chair (saved as wheelchair.java) class chair { public void adjustHeight() { System.out.println(“adjusting chair height”); } } //deriving wheelchair class from chair public class wheelchair extends chair { //overriding adjustHeight() method public void adjustHeight() { System.out.println(“adjust wheelchair height”); } Slide 74: public static void main (String args[]) { wheelchair w w = new wheelchair(); w.adjustHeight(); } } You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
java chapter-1 dineshkavitha Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1323 Category: Education License: All Rights Reserved Like it (8) Dislike it (0) Added: July 06, 2010 This Presentation is Public Favorites: 6 Presentation Description No description available. Comments Posting comment... By: ajaysuri (7 month(s) ago) pls send this ppt to my mail id:surekamca.d@gmail.com Saving..... Post Reply Close Saving..... Edit Comment Close By: anandsp1990 (7 month(s) ago) pls send this to my mail anandsp1990@gmail.com Saving..... Post Reply Close Saving..... Edit Comment Close By: simmipateriya (7 month(s) ago) pls send me this ppt to simmipateriya@gmail.com Saving..... Post Reply Close Saving..... Edit Comment Close By: JomonTJose (9 month(s) ago) Sir, please send this PPT to my mail id jomontjose@yahoo.co.in Saving..... Post Reply Close Saving..... Edit Comment Close By: udayachandra (11 month(s) ago) Sir please send the ppt to my mail id chandra.8686@gmail.com.. thanks a lot.. Saving..... Post Reply Close Saving..... Edit Comment Close loading.... See all Premium member Presentation Transcript Slide 1: UNIT - I CHAPTER – 1 java CONTENTS : CONTENTS 1. INTRODUCTION 1.1. history of java 2. STRUCTURE OF JAVA PROGRAM 2.1. standard program and Applets 2.2. packages 2.3. importing classes and Packages 3. THE JAVA COMPILER AND VIRUTAL MACHINE 4. DOCUMENTATION COMMENTS 5. DATA TYPES Slide 3: 6. METHODS 6.1. parameters 6.2. Overloaded Methods 7. EXCEPTIONS 7.1. throwing an exception 7.2. handling exceptions 8. ACCESS MODIFIERS 9. INHERITANCE AND METHOD OVERRIDING 9.1. Super-classes and Subclasses 10. GENERIC METHODS 11. GARBAGE COLLECTION 12. RECURSION 12.1. recursive function 12.2. induction 12.3. recursive methods Slide 4: 13. TESTING AND DUBUGGING 13.1. what is testing 13.2. designing test data 13.3. debugging 1. INTRODUCTION : 1. INTRODUCTION 1.1. HISTORY OF JAVA 1. Java programming language is usually associated with “ World Wide Web ”. 2. Java predates the Web. 3. Java began it’s life as the programming language “ Oak ”. 4. Oak was developed by the “Green Project Members” * Patrick Naughton * Mike Sheridan * James Gosling 5. A group formed in 1991 to create products for the “ Smart electronic Markets “ Slide 6: 6. The existing programming language were not suitable for “ consumer electronics “. 7. The Chief Programmer of Sun Microsystem – James Gosling : created the software for controlling “ Consumer Electronic devices “. 8. The team wanted a fundamentally new way of computing , based on the power of “ Networks “. And the S/W to run on different kinds of computers 9. Patenting issues gave a new name to Oak – Java. 10. HotJava - The first Java-enabled Web browser characteristics of java : characteristics of java Java is simple Java is object-oriented Java is distributed Java is interpreted Java is robust Java is secure Java is architecture-neutral Java is portable Java is high-performance Java is multithreaded Java is dynamic language Slide 8: Java is simple Java is simple language, can be learned easily. Java is object-oriented Java provides Abstraction, Encapsulation, Inheritance and Polymorphism. Java is distributed Java is tuned to the Web, So java program can access data – across the Web as easily as they access data from local system. Java is interpreted Java is both Interpreted and compiled. The code is complied to byte code that’s “ Binary “ and “ platform independent”. Slide 9: Java is robust Java forces the programmer to handle unexpected errors. This ensure that java programs are “Robust” (Reliable) and bug free and don’t crash. Java is secure A program traveling from internet to pc could possibly carry a virus. Java done strong type-checking on the user-machine, and changes in the program are tagged as errors and program will not executed. So, java is “secure”. . Java is architecture-neutral The byte code can be executed on a variety of computers running on different operating systems. Slide 10: Java is portable Java program can run on any machine that has a java interpreter. Other people can use the programs written in java, even if they have different machines with different operating systems. Java is multithreaded perform multiple task at the same time. Java is dynamic language Maintaining different versions of an application is very easy in Java. 2. STRUCTURE OF JAVA PROGRAM : 2. STRUCTURE OF JAVA PROGRAM Types of Java Programs are: 1. Applications (or) stand-alone program - they are program that don’t need a browser to run simultaneously. - need MS-DOS or UNIX prompt to execute the program. 2. Applets - Applets are programs that execute inside a Web page. - Applets require a Java enabled browser like * MS-internet Explorer * Netscape Navigator * Hotjava - Applet have Graphical User Interface. Slide 12: 3. Servlets - these programs extend the functionality of web servers 4. Packages - they are collections of classes that can be shared by other Java programs. 2.1. standard program and Applets : 2.1. standard program and Applets Every java program is a – CLASS Every class may contain data and METHOD members 2.2. packages : 2.2. packages DEFINITION A Package is a collection of classes that can be shared by java program. Packages are used to organize classes into groups. Types of Packages (i). Pre-defined (ii). User-defined 1. java.lang 2. java.util user can 3. java.applet create their 4. java.awt own packages 5. java.io (e.g) lab program 6. java.net Slide 15: 1. java.lang - provides classes and interfaces that are fundamental to java programming. 2. java.util - provides classes that support collections, data and calendar operations, parsing, internationalization and basic event processing. Also refers to all programs in the directory (lang/java or lang\java). 3. java.applet - provides classes, necessary for basic applet programming. 4. java.awt (abstract window toolkit) - provides classes for creating GUI programs. Slide 16: 5. java.io - provides classes for reading and writing data in the form of streams. (input stream, output stream) e.g: memory, file, buffer, network 6. java.net - provides classes that provide network programming. 2.3. importing classes and Packages : 2.3. importing classes and Packages Syntax for package import <package_name>.*; import <package_name> . <class_name>; Example: import java.awt.*; import java.awt.Button; import java.awt.*; in this syntax all the classes in awt package have to imported import java.awt.Button; in this syntax only button class from awt package have to imported 3. The java compiler and virtual machine : 3. The java compiler and virtual machine Java source code is converted into Java Byte code (or) J-code. * When the program <programName> is compiled, the program source code is read from the file <programName.java> * The compiled byte code is written in the file <programName.class> * Java Virtual Machine (JVM) is a software that interpret and executes the byte code. The main task of JVM is – the loading of .class files JVM- has class loaders that loads the .class files, and executed by the execution engine. Slide 19: Each java applications run inside a JVM. JVM starts when you start a java program and terminates when the program ends. The no. of JVM starts when you start a java program and terminates when the program ends. CLASS LOADER ARCHITECTURE 1. A JVM can have many class Loader. They provide security and network to java programs. 2. The JVM has two types of class loaders. (a) Primordial Class Loader (b) Class Loader Objects Slide 20: (a) Primordial Class Loader A primordial Class Loader is a part of the JVM implementation. It loads the java API classes when you execute a java program. (b) Class Loader Objects An application can create many class loaders at runtime for loading the classes of the application. Class Loader Class Loader Java API Primordial Class Loader Java Virtual Machine Implementation Implementation of Class Loader Slide 21: JAVA VIRUTAL MACHINE Slide 22: Through the Java VM, the same application is capable of running on multiple platforms. Slide 23: The Java platform has two components: – The Java Virtual Machine (JVM) – The Java Application Programming Interface (API) 4. DOCUMENTATION comments : 4. DOCUMENTATION comments A comment is a message for a programmer & describes a class, a method, or even a statement. The complier ignore what you write as comments Comments are ignored by the compiler but are useful to other programmers Java support three styles of comments: 1. Multiple line comments 2. Single line comment entries 3. The javadoc comments 1.Multiple line comments Anything you write between /* and */ is treated as a comment. The text that you type here can cover many lines. /* multiple line comments */ Slide 25: 2. Single line comment entries anything you type after // is treated as a comment. The text can’t span (extend) more than a line. If you have multiple lines as comments, you must start every line with //. // single line comment 3. The javadoc comments these lines are used by the javadoc utility to create documentation. These comments are similar o the multiple line comments but start with a /** instead of /* /** this is a javadoc comment*/ 5. DATA TYPES : 5. DATA TYPES The data that’s stored in memory can be of many types. For example: * a person’s age is stored as a numeric value & an address is stored as alphanumeric characteristics. * an address is stored as alphanumeric characters Data types are used to define the operations possible on them and the storage method. * The data types in java are classified as: 1. primitive (or) standard data types 2. Abstract (or) derived data types Slide 27: 1. primitive (or) standard data types 2. Abstract (or) derived data types : 2. Abstract (or) derived data types Abstract data types are based on primitive data types and have more functionality than primitive data types. Example “String” is an abstract data type that can store letters, digits and other characters like /,(), : , ; , $ , # * “String ”provides methods for concatenating two strings, searching for one string within another, and extracting a portion of a string. The primitive data types don’t have these features. 6. METHODS : 6. METHODS 1. parameters A method is a body of code that’s used for performing a set of tasks. The behavior of an object is determined by the program. Declaring Methods: syntax: [<access_specifier>] [<modifiers>] <return_type> <method_name> ([argument_list]) { //statements } Slide 31: Example: public static int abc (int a, int b, int c) { return a+b*c+b/c; } Where: abc - name of the method int - return type of the method is ‘int’ (int a, int b, int c) – formal paramenters of the method abc, each is of integer type. Slide 32: If the method is invoked by the statement Z = abc (2,x,y) then 2,x,y are the ‘actual parameter’. * when the method ‘abc’ is invoked the a - is assigned to 2 b - is assigned to x c - is assigned to y * In java all method parameters are ‘value parameters’. * At run time the value of each ‘actual parameter’ is copied into the corresponding format parameter before the method is executed. 2. Overloaded methods : 2. Overloaded methods Overloading is a technique in which more than one method having the same name can be present in a program. The compiler resolves the method to be invoked using the signature of the method. Function signature 1. The name of the method 2. The number of arguments it takes 3. The data type of the arguments 4. The order of the arguments - when we call a method, the compiler uses the signature of the method to resolve the method to be invoked. - A class can’t have two methods having the same signature. Slide 34: - this is because the compiler will not know which method to invoke if more than one method has the same signature. Example: java supports method overloading and hence, the methods can be declared as follows: * public void add(int a, int b); // add two integers * public void add(float a, float b); // add two floats * public void add(float a, int b); // adds a float and an integer * In the following example the ‘calculator’ class, the methods have the same name but different parameters and the signatures of the methods are different. Slide 35: class calculator { public int add(int a, int b) { System.out.println("int and int"); return a + b; } public float add(float a, float b) { System.out.println("float and float"); return a + b; } Slide 36: public float add(float a, int b) { System.out.println("float and int"); return a + b; } public static void main(String args[]) { calculator c = new calculator(); System.out.println(c.add(1,10)) System.out.println(c.add(1.6f,10.5f)); } } Slide 38: class calculator { public int add(int a, int b) { System.out.println("int and int"); return a + b; } public float add(float a, float b) { System.out.println("float and float"); return a + b; } Slide 39: public float add(float a, int b) { System.out.println("float and int"); return a + b; } public static void main(String args[]) { calculator c = new calculator(); System.out.println(c.add(1,10)) System.out.println(c.add(1.6f,10.5f)); System.out.println(c.add(10.5f,2)); } } 7. EXCEPTIONS : 7. EXCEPTIONS An exception is defined as an ‘abnormal’ event that occurs during program execution and disturb the normal flow of instructions. Error-handling becomes necessary, when developing applications and need to take care of unexpected situations. The unexpected situations that may occur during program execution are: * Running out of memory * Resource allocation errors * Inability to find files * Problems in network connectivity Exception-Handling Techniques : Exception-Handling Techniques When an unexpected error occurs in a method, java creates an object of the types ‘ Exception’. After creating the Exception object, java sends it to the program, by an action called “throwing an exception”. The Exception object contains information about the - type of error - status of the program when the exception occurred * Key words in Excepting: try catch throw throws finally Slide 43: Try Block syntax: try { //statements that may cause an exception } * If an exception occurs within the try block, the appropriate exception-handler that’s associated with the try block handles the exception. * A try block must have at least one catch block that follows it immediately. Slide 44: catch Block syntax: try { //statements that may cause an exception } catch(……) { // error handling routines } The catch statement take the object of the exception class that refers to the exception caught. Once the exception is caught, the statements within the catch block are executed. The scope of the catch block is based on the statement in the preceding try block. Exception handling mechanism : Exception handling mechanism In java, exception-handling facility handles abnormal & unexpected situation in a structured manner. When an exception occurs, the java runtime system searches for an exception-handler (try-catch-block). If a handler is not found in the current method, the handler is searched for in the ‘calling method’. The searches goes on till the runtime system finds an appropriate exception-handler. EXAMPLE: // derivedclass.java class baseclass { public int divide(int num1, int num2) { Slide 46: return num1 / num2; } } public class derivedclass extends baseclass { public int divide(int a, int b) { return super.divide(a,b); } public static void main(String args[]) { int result = 0; derivedclass d1 = new derivedclass(); Slide 47: try { result = d1.divide(100, 0); } catch(ArithmeticException e) { System.out.println(“Error…division by zero”); } System.out.println(“The result is: “ + result”); } } Multiple catch block - example : Multiple catch block - example public class trycatch { public static void main(String args[]) { int num1, num2, result = 0; num1 = 100; num2 = 0; try { result = num1/num2; } Slide 50: catch(ArithmeticException e) { System.out.println("Error---division by zero"); } catch(ArrayIndexOutOfBoundsException e) { System.out.println("Error----out of bounds"); } catch(Exception e) { System.out.println("some other error"); } System.out.println("The result is: " + result); } } Slide 52: EXAMPLE-2 public class trycatch { public static void main(String args[]) { int num1, num2, result = 0; num1 = 100; num2 = 4; try { result = num1/num2; } Slide 53: catch(ArithmeticException e) { System.out.println("Error---division by zero"); } catch(ArrayIndexOutOfBoundsException e) { System.out.println("Error----out of bounds"); } catch(Exception e) { System.out.println("some other error"); } System.out.println("The result is: " + result); } } throw statement : throw statement When a user enters a wrong login-ID (or) password, the throw statement is used to throw an exception. The throw statement takes a single statement, which is an object of the ‘Exception class’. Syntax throw Throwableinstance; * Example throw ThrowObject; The compiler gives an error if the object ‘ThrowObject” doesn’t belong to a valid ‘Exception class’. The ‘throw statement is commonly used in ‘programmer-defined’ exceptions. throws statement : Throws statement is used to specify that ‘ an exception has to be handled by the calling method. It’s used for an exception that a method is capable of raising, but not handling. Syntax [<access_specifier>][<modifier>]<return_type> <method_name> (<arg_list>) [throws <exception_list>] Example public void acceptpassword() throws IllegalAccessException { System.out.println(“ intruder !!”); throw new IllegalAccessException; } throws statement Finally Block : Finally Block The finally block is used when it’s necessary to process certain statements no matter, whether an exception is raised or not. Example try { openFile(); writeFile(); // may cause an exception } catch(……..) { // process the exception } Finally { closeFile(); } Common exceptions : Common exceptions 1. ArithmeticException Exception 2. NullPointerException Exception 3. ArrayIndexOutofBoundsException Exception 8. ACCESS MODIFIERS : 8. ACCESS MODIFIERS An access specifier determines which features of a class (the class itself, the data members, and the method) may be used by the other classes. Java supports three specifiers (or) Access Modifiers 1. public 2. private 3. Protected 4. Default Public access specifier A class, data member (or) method that has a public access specifier can be accessed by any object. An inner class can’t have a public access specifier. Slide 60: Syntax <access_specifier> <return_type> <method> ([argment list]) { ---------- } Example: public class employee { string empname; string empadd; public void displaydetails( ) { // place the code for displaying employee details } } 2. Private access specifier : 2. Private access specifier Only object of the same class can access a variable or a method that has a private access specifier. The variables and method of the inner classes can be declared as private. Example: private int privateVariable; 3. Protected access specifier variable, methods, and inner classes that are declared protected accessible to the subclasses of the class in which they are declared. Example: protected int protectedVariable Slide 62: 4.Default access A class, a variable or a method that doesn’t have an access specifier as private, public, protected is said to have default access. These classes, variables or methods are accessible to all the classes of a package. Example: consider following set of classes y and z inherit from class x. class z belongs to the package p1 and classes x and y belong to the package p2. Class X Class Y Class Z Package p1 Package p2 Slide 63: * A method accesme() has been declared in class X. The following table shows the accessibility of the method accessme() from class Y and Z. MODIFIERS : MODIFIERS Modifiers determine how the data members and methods are used in other classes and objects. The modifiers in java: 1. static 2. final 3. abstract 4. native 5. transient 6. synchronized 7. volatile 9. INHERITANCE AND METHOD OVERRIDING : 9. INHERITANCE AND METHOD OVERRIDING Inheritance is a situation in which a class derives a set of attributes and related behavior from a parent class. 9.1. super classes and subclasses: * super class: super class is a class from which another class inherits properties. It share its properties with its child classes. * sub class: sub class is a class that inherits attributes and methods from a super class. Slide 67: Super class some times referred to as the ‘base class’ and the subclass is referred to as the ‘derived class’. Subclass don’t inherit the constructs of the super class. Example: let us take the example of ‘air tickets’- it can be of two types. Confirmed and request ticket. both the tickets have a lot of common attributes. For example flight_number, date, time and destination. confirmed ticket would have a ‘seat number’, while a request ticket would have a ‘status’. Slide 68: Example: Syntax: public class <subclass name> extends <superclass name> public class confirmedTicket extends Ticket Ticket RequestTicket ConfirmedTicket Final keyword : Final keyword The final modifier doesn’t allow a class to be inherited. A method declared anal can’t be overridden by a subclass. Final- keyword can prevent people from extending a class by using the ‘final’ modifier as follow: example: final class password { -------- } OVERRIDING methods : OVERRIDING methods In overridding, a subcalss method overrrides the definition of a super class method, if the method defined in the subcalss has the same signature of a method in the super class. Example: let us consider the class ‘wheelchair’ is derived from the ‘chair class’. Both the classes have a method called ‘adjustHeight()’. Wheelchair is adjusted differently form the way other chairs are adjusted. Therefore, the wheelchair class overrides superclass method ‘adjustHeight()’. Slide 71: // declaring base class chair (saved as wheelchair.java) class chair { public void adjustHeight() { System.out.println(“adjusting chair height”); } } //deriving wheelchair class from chair public class wheelchair extends chair { public static void main (String args[]) { wheelchair w w = new wheelchair(); w.adjustHeight(); } } Slide 73: // declaring base class chair (saved as wheelchair.java) class chair { public void adjustHeight() { System.out.println(“adjusting chair height”); } } //deriving wheelchair class from chair public class wheelchair extends chair { //overriding adjustHeight() method public void adjustHeight() { System.out.println(“adjust wheelchair height”); } Slide 74: public static void main (String args[]) { wheelchair w w = new wheelchair(); w.adjustHeight(); } }