Question

If I have a member variable such as this (declared in the body of a class)

private Dot[] dots=new Dot[numDots]; 

I loop through all members of this array, and:

1) Pass every Dot object to a function of another class, which:

2) Passes it to yet another function of a 3rd class, if some conditions are met

3) And the 3rd class changes some properties of the Dot object

then when this object is returned to the original/parent class, would those changes to its properties have retained? Or would it be treated like a local variable by the 2nd/3rd functions?

Answer 1

Yes, the changes to the properties are retained. Java is 100% pass-by-value, however, when you pass an object, the ‘value’ passed is truly a pointer to the object. Thus, when you change an object in a method, you’re changing the actual object passed in.

That is, if you have the following method, then the calling method will see the changes:

private void updateMyDot(final Dot aDot) {   aDot.dotColor = new Color(255,255,255); } 

but if you do the following, then the calling method will not see the changes.

private void updateMyDot(/* not final */ Dot aDot) {   aDot = new Dot();   aDot.dotColor = new Color(255,255,255); } 

In the second example, the caller will not see any changes and will not see the newly created Dot object.