Object Reference Variables

Assigning Object Reference Variables : Concept in Java Programming

1. We can assign value of reference variable to another reference variable.
2. Reference Variable is used to store the address of the variable.
3. Assigning Reference will not create distinct copies of Objects.
4. All reference variables are referring to same Object.

Assigning Object Reference Variables does not 

1. Create Distinct Objects.
2. Allocate Memory
3. Create duplicate Copy

Consider This Example –

Box b1 = new Box();
Box b2 = b1;

• b1 is reference variable which contain the address of Actual Box Object.
• b2 is another reference variable
• b2 is initialized with b1 means – “b1 and b2” both are referring same object , thus it does not create duplicate object , nor does it allocate extra memory.

Example : Assigning Object Reference Variables

class Box {
  double width;
  double height;
}

class BoxExample {
  public static void main(String args[]) {

  Box b1 = new Box();
  Box b2 = b1;

  b1.width = 10;
  b2.height = 20;

  System.out.println("Value of Box1's Height : " + b2.height);
  System.out.println("Value of Box2's Height : " + b2.height);

  }
}

Output :

C:Zubair>java BoxExample
Value of Box1's Height : 20.0
Value of Box2's Height : 20.0

Concept :

Suppose we have assigned null value to b2 i.e

Box b1 = new Box();
Box b2 = b1;
.
.
.
b1 = null;

Note : Still b2 contain reference to an object. Thus We can create have multiple reference variables to hold single object.

Another Example to understand about reference objects

One or more objects of the same class