memoize a java function

Memoize.java

import java.util.*;
import java.util.function.Function;

public class Memoize {
	static interface F<T,R> extends Function<T,R> {}
	
	// not thread safe
	static <T,R> F<T, R> memoize(F<T, R> f) {
		Map<T, R> cache = new HashMap<>();
		return (x) -> {
			cache.putIfAbsent(x, f.apply(x));
			return cache.get(x);
		};
	}

	static int longComputation(int x) {
		try { Thread.sleep(1000); } catch (Exception e) {}
		return x;
	}

	public static void main(String[] args) {
		F<Integer, Integer> f = memoize(Memoize::longComputation);
		System.out.println(f.apply(3));
		System.out.println(f.apply(3));
	}
}