Question

I read with interest this question :
Can I pass parameters by reference in Java?

What comes out it is that parameters (which are not primitives) are passed by copying the reference value.
And so as the example states; you can’t modify the reference of the parameter you gave:

Object o = "Hello";
mutate(o)
System.out.println(o); // Will print Hello

private void mutate(Object o) { o = "Goodbye"; } //NOT THE SAME o!

This kind of problem could be avoided using finallike this :

private void mutate(final Object o) { o = "Goodbye"; } //Compilation error

The questions :

• Is the final keyword in such a case only used to throw a compilation error ?
• If in the end you can’t modify the reference of the given parameter why isn’t final implicit or mandatory ?

I rarely used final for method parameters in Java but now I can’t think of any case where you would voluntarily omit to put final to a method parameter.

Thanks!

Answer 1

Typically you shouldn’t modify parameters as it can introduce hard to find bugs. However there are some useful idioms and situations where it can be useful:

public void print(String msg, int count) {
    msg = (msg != null)? msg : "Default";
    while(--count >= 0) {
        System.out.println(msg);
    }
}