My take on a java promise interface

Promise.java

public interface Promise<T> {

	Promise<T> resolve(T value);

	Promise<T> resolve(Promise<T> promise);

	Promise<Throwable> reject(Throwable e);

	Promise<T> then(CallbackFunction onResolved);

	Promise<T> then(CallbackFunction onResolved, CallbackFunction onError);

	Promise<T> then(CallbackFunction onResolved, CallbackFunction onError,
			CallbackFunction onNotify);

	Promise<T> ensure(CallbackFunction handler);

}