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

Consider making an anonymous local class and using its initializer block to do the work:

public class LocalFunctionExample {
    public static void main(final String[] args) {
        for (final int i[] = new int[] { 1 }; i[0] < 100; i[0]++) {
            new Object() {
                {
                    times(2); //multiply i by 2 and print i
                    times(i[0]); //square i and then print the result
                }

                public void times(final int num) {
                    i[0] *= num;
                    System.out.println(i[0]);
                }
            };
        }
    }
}

Output:

2
4
10
100

(The "final wrapper trick" is not automatically required with this technique, but was needed here to handle the mutation requirement.)

This works out to be almost as concise as the lambda version, but you get to use whatever method signatures you want, they get to have real parameter names, and the methods are called directly by their names - no need to .apply() or whatnot. (This kind of thing sometimes makes IDE tooling work a little better too.)