3-0 classespolymorphism n inheritance3-1 classobject n method

7/30/2019 3-0 Classespolymorphism n Inheritance3-1 Classobject n Method

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Introduction To Java Programming1.0 Basic Concepts of Java Programming2.0 Classes, Polymorphism and Inheritance

3.0 Exception handling4.0


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Create classes and declare their membersin Java programme.1

Define method and identify its uses.2

Add methods in Java programmes.3

Identify the built-in methods in Javalibrary.4

Write Java programme using methods.5


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Create objects for a class in Javaprogrammes.6

Develop Java programme using classesand objects.7

Define constructors and identify its uses.8

Add constructors in Java programmes.9

Write Java programme using

constructors.10


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Introduction

Java is an object-oriented programming language.

The concept behind object-oriented programmingis implemented in Java using classes and objects.

Classes A class is a user-defined data type. Class is acontainer which holds variables and methods .

Objects The Objects are created to access thevariables and methods from classes.


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Example - Creating a Class

class Book

{ //body of the class Book }


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Variable and Method Declaration Variables and methods are declared in the body of class. Methods are necessary for operating with the data contained in the class.

Method declarations have four basic parts:

The name of the method ( methodname ).The type of the value the method returns ( type ).

A list of parameters ( parameter-list ).

The body of the method.


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Variable and Method Declaration class Act5F {

String name, int age;

void insert(String n, int a) {

name = n; age = a;

}void show()

{ System.out.println (My Name is + name); System.out.println (My Age is + age);

} public static void main(String[]args)

{ Act5F obj = new Act5F();

obj.insert (Nabila, 15); obj.show();

} }


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Creating Objects Object is an entity that consists of variables and methods to manipulate those

variables.

The class members can be accessed through objects.

For example, create an object for class Book.

Book b1; b1 = new Book( );

@Book b1 = new Book( );


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Creating Objectsclass Act5F {



name = n; age = a;

}void show()


} public static void main(String[]args){

Act5F obj = new Act5F();obj.insert (Nabila, 15); obj.show();

}}


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Assigning Object Reference

You can create an object for a class and assignit to another object.

Book b1 = new Book( );Book b2 = b1;


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Assign Value to Instance Variables

You can assign values to the Instance variablesthrough the methods and access the class members.

ExampleBook b1 = new Book( );

b1.getData("Java 2 A Beginner's Guide","Herbert Schildt",100);


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class Act5F {



name = n; age = a;

}void show()


} public static void main(String[]args) {

Act5F obj = new Act5F(); obj.insert (Nabila, 15); obj.show();

} }

Assign Value to Instance Variables


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Syntax to Assign Value to Instance Variables

.(parameter-list);

Here,1. objectname is the name of the object.2. methodname is the method of the class that you

wish to call. 3. Parameter-list is the comma separated list of

values that must match in type and number withthe parameter list of the methodname declared inthe class.


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Access Data members in a class

The data members in a class is accessedusing the dot operator.

Example :b1.book_name = "Java 2 A Beginner's Guide";b1.author_name = "Herbert Schildt ; b1.no_of_pages = 100;


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Constructors

Is a special method that enables an object to

initialise itself when it is created. It is used to initialise the data members of a class.

Constructor gets automatically called when an

object is created.


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Constructors

Characteristics of Constructors Constructors have the same name as the class name. The constructor allocates sufficient memory space for

the object. They do not return any value. The syntax of a constructor is similar to that of a

method. Once defined the constructor is automatically called

immediately when the object is created before thenew operator completes its job. Java creates a default constructor when you do not

define a constructor.


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Example - Constructor class Book {Book(String bname, String aname, int nopages){

book_name = bname;

author_name = aname;no_of_pages = nopages;

}public static void main(String args[])

{Book b1 = new Book ("Java 2","HerbertSchildt",100);}

}


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Example without Constructor class Book {void getData(String bname, String aname, int nopages){

book_name = bname;

author_name = aname;no_of_pages = nopages;

}public static void main(String args[])

{Book b1 = new Book ();b1.getData ("Java 2","Herbert Schildt",100);}

}

3-0 classespolymorphism n inheritance3-1 classobject n method

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