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.

Answer 1

You could interface static methods. This method allows you to specify parameters too. Declare your interface...

public interface RouteHandler {
    void handleRequest(HttpExchange t) throws IOException;
}

And your map...

private Map routes = new HashMap<>();

Then implement static methods that match the interface/params...

public static void notFound(HttpExchange t) throws IOException {
    String response = "Not Found";

    t.sendResponseHeaders(404, response.length());
    OutputStream os = t.getResponseBody();
    os.write(response.getBytes());
    os.close();
}

You can then add those methods into your map...

routes.put("/foo", CoreRoutes::notFound);

and call them as follows...

RouteHandler handler = routes.get("/foo");
handler.handleRequest(exchange);