How can you extend Java to introduce passing by reference?

Question

Java is pass-by-value. How could you modify the language to introduce passing by reference (or some equivalent behavior)?

Take for example something like

<         


        

Answer 1

Your attempt to modify the language ignores the fact that this "feature" was explicitly left out to prevent well-known side-effect bugs from being able to happen in the first place. Java recommends to do what you are trying to archive by the use of data-holder classes:

public class Holder {
  protected T value;

  public T getValue() {
    return value;
  }

  public void setValue(T value) {
    this.value = value;
  }
}

A thread-safe version would be the AtomicReference.

Now storing a single String in a class seems over-kill and most likely it is, however usually you have a data-holder class for several related values instead of a single String.

The big benefit of this approach is that what happens inside the method is very explicit. So even if you are programming on a Monday morning after an eventful weekend and the coffee machine just broke down, you still can tell easily what the code is doing (KISS), preventing several bugs from even happening in the first place, just because you forgot about that one feature of method foo.

If you think about what your approach can do that the data-holder version cannot, you'll soon realize that you are implementing something just because it is different, but effectively it has no real value.