Declaring objects

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 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 e.g. chair, bike, marker, pen, table, car etc. It can be physical or logical (tangible and intangible). The example of intangible 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.

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.

Object Definitions:

• Object is a real world entity.
• Object is a run time entity.
• Object is an entity which has state and behavior.
• Object is an instance of a class.

Simple Example of Object and Class

In this example, we have created a Employee class that have two data members eid and ename. We are creating the object of the Employee class by new keyword and printing the objects value.

Example

class Employee
{
 int eid;  // data member (or instance variable)
 String ename;  // data member (or instance variable)
 eid=101;
 ename="Hitesh";
 public static void main(String args[])
 { 
  Employee e=new Employee(); // Creating an object of class Employee
  System.out.println("Employee ID: "+e.eid);
  System.out.println("Name: "+e.ename);
 }  
}  

Output

Employee ID: 101
Name: Hitesh