How to do “call by reference” in Java?

Question

Real pass-by-reference is impossible in Java. Java passes everything by value, including references. But you can simulate it with container Objects.

Use any of these as a method parameter:

an array
a Collection
an AtomicXYZ class

And if you change its contents in a method, the changed contents will be available to the calling context.

Oops, you apparently mean calling a method by reference. This is also not possible in Java, as methods are no first-level citizens in Java. This may change in JDK 8, but for the time being, you will have to use interfaces to work around this limitation.

public interface Foo{
    void doSomeThing();
}

public class SomeFoo implements Foo{
    public void doSomeThing(){
       System.out.println("foo");
    }
}

public class OtherFoo implements Foo{
    public void doSomeThing(){
       System.out.println("bar");
    }
}

Use Foo in your code, so you can easily substitute SomeFoo with OtherFoo.

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