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Object and class in java


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Object and class in java

Hi everyone in this blog we will learn about java object and classes.

Introduction:

In object-oriented programming technique, we design a program using objects and classes.

Object is the physical as well as logical entity whereas class is the logical entity only.

Object in java:

An entity that has state and behavior is known as an object like chair, bike, marker, pen, table, car etc. It can be physical or logical (tengible and intengible). The example of integible object is banking system.

An object has three characteristics:

v  state: represents data (value) of an object.

v  behavior: represents the behavior (functionality) of an object such as deposit, withdraw etc.

v  identity: Object identity is typically implemented via a unique ID. The value of the ID is not visible to the external user. But,it is used internally by the JVM to identify each object uniquely.

For Example: Pen is an object. Its name is Reynolds, color is white etc. known as its state. It is used to write, so writing is its behavior.

Object is an instance of a class. Class is a template or blueprint from which objects are created. So object is the instance(result) of a class.

Class in java:

A class is a group of objects that has common properties. It is a template or blueprint from which objects are created.

A class in java can contain:

v  data member

v  method

v  constructor

v  block

v  class and interface

 

Syntax to declare a class:

class class_name

{

      data member;

     method;

}

 

Example:

class Sample

{

                Int id;

                String name;

                public static void main(String … s)

                {

                                Sample obj=new Sample();

                                System.out.println(obj.id);

                                System.out.println(obj.name);

}

}

 

Output:

0 null

Instance variable in java:

Instance variable is created inside the class but outside the method, is known as instance variable. Instance variable is not get memory at compile time. Instance variable get memory at run time when object is created.

Creating multiple objects by one type only:

We can create multiple objects by one type only as we do in case of primitives.

Sample obj1=new Sample(),obj2=new Sample();//Two object created in this line

Example:

class Sample

{

                void add(int a, int b)

                {

                                System.out.println(a+b);

}

                public static void main(String … s)

                {

                                Sample obj1=new Sample(),obj2=new Sample();

                   obj1.add(10,20);

                   obj2.add(45,20);

}

}

Output:

30

65


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