Function pointers/delegates in Java?

Question

For my Java game server I send the Action ID of the packet which basically tells the server what the packet is for. I want to map each Action ID (an integer) to a function. Is there a way of doing this without using a switch?

Answer 1

What about this one?

HashMap<Integer, Runnable> map = new HashMap<Integer, Runnable>();
map.put(Register.ID, new Runnable() { 
    public void run() { functionA(); }
});
map.put(NotifyMessage.ID, new Runnable() { 
    public void run() { functionB(); }
});
// ...
map.get(id).run();

(If you need to pass some arguments, define your own interface with a function having a suitable parameter, and use that instead of Runnable).

Answer 2

Another similar approach could be using Java 8's Suppliers:

Map<Integer, Supplier<T>> suppliers = new HashMap();

suppliers.put(1, () -> methodOne());
suppliers.put(2, () -> methodTwo());

// ...

public T methodOne() { ... }
public T methodTwo() { ... }

// ...

T obj = suppliers.get(id).run();