Unclear about pass by reference

[Anand Kumar Loganathan]

public class ReferenceTester {

	public Integer i=new Integer(0);
	public static void main(String[] args) {

		ReferenceTester rt = new ReferenceTester();
		Integer intt=new Integer(0);
		
		System.out.println(intt +"," + rt.i);
		change(rt,intt);
		System.out.println(intt +"," + rt.i);

	}
	
	static void change(ReferenceTester rt,Integer intt){
		rt.i=20;
		intt =20;
		
	}
}

The output is

0,0
0,20

But i was expecting it to be


0,0
20,20 as both rt and intt are object references. Is my understanding correct?.

[Stephan van Hulst]

No. Java is pass by value, so you can't do this.

You just passed an object reference by value. Pass by reference means passing variables by reference.

[Ralph Cook]

The other thing that may not be obvious is that, within the method change(), the statement

rt.i=20;

assigns a value to an instance variable within the same rt object referenced by the caller . But the statement

intt = 20;

creates a new Integer object to assign and assigns it to intt.

So the second statement changes the value of the object reference itself, and that does not affect the caller's reference.

You can read more about the creation of a new object for Integer by looking up "autoboxing".

[Anand Kumar Loganathan]

Thanks Stephen and Ralph!!!