Pass By Value

[Raja Narasimha]

Hi, Why "420" prints at Line 22 instead of "99" ?

class PassByValueTest {
    int num = 28;
}

class Test2 {
    PassByValueTest test1Ref = new PassByValueTest();

    void changeIt(int num) {
	test1Ref.num = 99;
	System.out.println("1st time  " + test1Ref.num);
	test1Ref = new PassByValueTest();
	test1Ref.num = 420;
	System.out.println("2nd time  " + test1Ref.num);
    }
}

public class P217_PassByValue01_Ask {
    public static void main(String[] args) {
	Test2 test2Ref = new Test2();
	System.out.println("f.test1Ref.num old " + test2Ref.test1Ref.num);
	test2Ref.changeIt(test2Ref.test1Ref.num);
	System.out.println("f.test1Ref.num new " + test2Ref.test1Ref.num);//why 420 prints here ??
    }
}

[Paul Clapham]

The short answer is: because that's how Java works. It would be more practical if you explained why it should be 99, and then somebody could explain what your misunderstanding was.

[Raja Narasimha]

There should be some strong concrete reason because "Java" is created by Human beings. So, I believe that every question that we discuss in this Java forum has a very well valid reason. Hence, Please do not mislead others.
Coming back to the requested information, Because "num" variable is of primitive int type, any changes that you make at Line 11 should not be in scope once method at Line 14 is completed. Please let me know if my assumption is wrong.

[varun Dosapati]

HI Raja

In the code the main class is "P217_PassByValue01_Ask", which created an object "Test2 " which is referred with "test2Ref " at line 19.

In "Test2 " created an object of "PassByValueTest " with a reference "test1Ref " at line 06 in turn created a new object "PassByValueTest " with same reference "test1Ref " at line 11.

So in the program at line 22 "test2Ref.test1Ref.num" refers to the second object of "PassBy ValueTest" which has "num" value 420


Regard
varun

[Mohamed Sanaulla]

At line 11 and 12- You are creating a new PassByValueTest and assigning a new value to the num.

In Java- Its always pass by value. So if you have Object references being passed around- We are actually copying the address/location of the Object. That way any changes made to the fields of the object gets reflected in other methods.