Nested functions in Java

Question

Are there any extensions for the Java programming language that make it possible to create nested functions?

There are many situations where I need to create methods

Answer 1

I think that the closest you can get to having nested functions in Java 7 is not by using an anonymous inner class (Jon Skeet's answer), but by using the otherwise very rarely used local classes. This way, not even the interface of the nested class is visible outside its intended scope and it's a little less wordy too.

Jon Skeet's example implemented with a local class would look as follows:

public class Test {
    public static void main(String[] args) {
        // Hack to give us a mutable variable we can
        // change from the closure.
        final int[] mutableWrapper = { 0 };

        class Foo {
            public void bar(int num) {
                mutableWrapper[0] *= num;
                System.out.println(mutableWrapper[0]);
            }
        };

        Foo times = new Foo();

        for (int i = 1; i < 100; i++) {
            mutableWrapper[0] = i;
            times.bar(2);
            i = mutableWrapper[0];

            times.bar(i);
            i = mutableWrapper[0];
        }
    }
}

Output:

2
4
10
100