Question

I came across something that I could not comprehend and never realized it could be done.

I was playing around with this block of code in Android, and what intrigued me was this:

public boolean onTouch(View v, MotionEvent event){
    Rect outRect = new Rect();
    _btn.getHitRect(outRect);
    // ... rest of code cut
    // outRect fields of that Rect object is 'filled' in.
}

How is it that Android’s Java can directly modify a Rect object outRect which was passed into the method in order to obtain the Rect of a button widget.

That surprised me, as I thought there was no such thing as ‘pass by reference‘ in Java, in Java parlance, using a ‘call-by-reference‘ rather, its ‘pass by value‘ or ‘call-by-value‘?

Yes, I have read this question asked before but am stumped, or is that an Android thing?

Can anyone shed some light on this?

Answer 1

The outRect reference is passed to the getHitRect method, which then modifies the object referred to by outRect. References are passed by value.

For a detailed explanation of this, read this article: http://javadude.com/articles/passbyvalue.htm