Object And Classes

Object and Class in Java

Object is the physical as well as logical entity whereas class is the logical entity only.In this page, we will learn about java objects and classes. In object-oriented programming technique, we design a program using objects and classes.

Object in Java

An entitythat has state and behavior is known as an object e.g. 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:

• state: represents data (value) of an object.
• behavior: represents the behavior (functionality) of an object such as deposit, withdraw etc.
• 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.

  Simple Example of Object and Class

  In this example, we have created a Student class that have two data members id and name. We are creating the object of the Student class by new keyword and printing the objects value.
  1. class Student1{  
  2.  int id;//data member (also instance variable)  
  3.  String name;//data member(also instance variable)  
  4.   
  5.  public static void main(String args[]){  
  6.   Student1 s1=new Student1();//creating an object of Student  
  7.   System.out.println(s1.id);  
  8.   System.out.println(s1.name);  
  9.  }  
  10. }  

  11. Example of Object and class that maintains the records of students

      In this example, we are creating the two objects of Student class and initializing the value to these objects by invoking the insertRecord method on it. Here, we are displaying the state (data) of the objects by invoking the displayInformation method.

      1. class Student2{  
      2.  int rollno;  
      3.  String name;  
      4.   
      5.  void insertRecord(int r, String n){  //method  
      6.   rollno=r;  
      7.   name=n;  
      8.  }  
      9.   
      10.  void displayInformation(){System.out.println(rollno+" "+name);}//method  
      11.   
      12.  public static void main(String args[]){  
      13.   Student2 s1=new Student2();  
      14.   Student2 s2=new Student2();  
      15.   
      16.   s1.insertRecord(111,"Karan");  
      17.   s2.insertRecord(222,"Aryan");  
      18.   
      19.   s1.displayInformation();  
      20.   s2.displayInformation();  
      21.   
      22.  }  
      23. }