Question

recently I’m writing some functions that I take from Haskell and translate into Java.
One of the main problems I have is I cannot easily create a static property with a generic type. Let me explain by a little example…

// An interface to implement functions
public interface Func<P, R> {
    public R apply(P p);
}

// What I want to do... (incorrect in Java)
public class ... {
    public static <T> Func<T, T> identity = new Func<T, T>() {
        public T apply(T p) { return p; }
    }
}

// What I do right now
public class ... {
    private static Func<Object, Object> identity = new Func<Object, Object>() {
        public Object apply(Object p) { return p; }
    }
    @SuppressWarnings("unchecked")
    public static <T> Func<T, T> getIdentity() {
        return (Func<T, T>)identity;
    }
}

Are there any easier ways to do something like that?
What kind of problems might arise if the syntax I used would be valid?

Answer 1

Just create a new tiny little object each time, for some definition of “each time”. Remember that allocations on typical JREs are tiny, but GCing static data is expensive.

Whilst I think your syntax could be made to work without compatibility issues, it would be add complexity and irregularity whilst not bringing a huge amount on benefit.