Java – call by value and call by reference

call by value in Java:

If a method is to be called by passing a parameter as a value then it is said to be Call by Value. Here the changes made to the passed parameter do not affect the called method.

Example of call by value:

  class CallByValue
  {
   void meth(int x, int y)
   {
     x = x + 10;
     y = y - 20;
    
     System.out.println("The result after the operation performed:");
     System.out.println("a = " + x + "\t b = " + y);
   }
  }
  
  public class JavaMain
  {   
   public static void main(String args[])
   {
    
    CallByValue obj = new CallByValue();
    
    int a =50, b = 100;
    
    System.out.println("The value of a and b before the call :");
    System.out.println("a = " + a + "\t b = " + b);
    
    obj.meth(a, b);
    
    System.out.println("The value of a and b after the call : ");
    System.out.println("a = " + a + "\t b = " + b);
      
   }
  }   

Output:

 a = 50	 b = 100
 The result after the operation performed:
 a = 60	 b = 80
 The value of a and b after the call : 
 a = 50	 b = 100

call by reference in Java:

If a method is to be called by passing a parameter (not the value) as a reference then it is said to be Call by Reference. Here the changes are made to the passed parameter effect on the called method.

Example of call by reference:

class CallByRef 
  {
    int x, y;
    
    CallByRef(int i, int j)
    {
        x = i;
        y = j;
    }
    
    /* pass an object */
    void method(CallByRef p)
    {
        p.x = p.x + 2;
        p.y = p.y + 2;
    }
  }
  
  public class JavaMain 
  {   
   public static void main(String args[])
   {
      
    CallByRef obj = new CallByRef(10, 20);
    
    int x = 10, y = 20;
    
    System.out.println("The value of a and b before the call :");
    System.out.println("a = " + obj.x + "\t b = " + obj.y);
    
    obj.method(obj);
    
    System.out.println("The value of a and b after the call : ");
    System.out.println("a = " + obj.x + "\t b = " + obj.y);
       
   }
  } 

Output:

 The value of a and b before the call :
 a = 10	 b = 20
 The value of a and b after the call : 
 a = 12	 b = 22

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