Function decorators using Java8 lambdas

Tools.java

package repl;

import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;

public class Tools {

    public static final boolean CACHE_ON = true;
    public static final boolean TIMER_ON = true;

    private static <T, K> Function<T, K> timer(Function<T, K> f) {
        if( !TIMER_ON ) return f;

        Function<T, K> fun = (args) -> {
            long time = System.currentTimeMillis();
            K ret = f.apply(args);
            time = System.currentTimeMillis() - time;
            System.out.println("time = " + time);
            return ret;
        };
        return fun;
    }

    private static <T, K> Function<T, K> cache(Function<T, K> f) {
        if(!CACHE_ON) return f;

        Map<T, K> cache = new HashMap<>();
        Function<T, K> fun = (args) -> {
            K ret = cache.get(args);
            if( ret == null ) {
                ret = f.apply(args);
                cache.put(args, ret);
            }
            return ret;
        };
        return fun;
    }

    private static Function<Integer, Long> fib = cache(n -> {
        if (n == 0 || n == 1) return 1L;
        return Tools.fib.apply(n - 1) + Tools.fib.apply(n - 2);
    });

    public static void main(String[] args) {
        Function<Integer, Long> tfib = timer(fib);
        long res = tfib.apply(45);
        System.out.println("res = " + res);
    }

}