Trying to make a closure in Java

test-closure.java

import java.util.concurrent.atomic.AtomicReference;

public abstract class TestClosure {
  public abstract int execute(int a);
}

public class MainClass {
	public static void main(String[] args) {
		final AtomicReference<Integer> x = new AtomicReference<Integer>(4);
		TestClosure testClosure = new TestClosure() {
			
			@Override
			public int execute(int a) {
				x.set(x.get()+1);
				return a+x.get();
			}
		};
		System.out.println(testClosure.execute(2));
		System.out.println(x.get());
	}
}