Accumulator by Java

gistfile1.java

interface Function1<A, R> {
    R apply(A arg);
}

class Holder<T> {
    public T value;
    public Holder(T value) {
        this.value = value;
    }
}

public class ClosureTest {
    static Function1<Integer, Integer> accumulator(int n) {
        final Holder<Integer> holder = new Holder<Integer>(n);

        return new Function1<Integer, Integer>() {
            public Integer apply(Integer i) {
                return holder.value += i;
            }
        };
    }

    public static void main(String[] args) {
        Function1<Integer, Integer> acc = accumulator(0);

        for (int i = 1; i <= 5; ++i)
            System.out.println(acc.apply(i * 2));
    }
}

// $ java ClosureTest
// 2
// 6
// 12
// 20
// 30