case expressions must be constant expressions gameDevelopment

Question

I have an assignment to build a game bord... I want the user to put the in program the keys he wants to play with. The problem is that Java requires that the values ​​in the switch case will be const... The idea is to create a type inheritance to the KeyListener and then I just add it to his proper player.

the desired Keys are received as a parameter int[] keys

I've seen some people offering a solution for similar problems by adding "static final" unfortunately it does not help

here is my code :

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class PlayerKeyListener implements KeyListener
{

int[] keys;
int playerID;

PlayerKeyListener(int[] keys, int playerID)
{
    this.keys = keys;
    this.playerID = playerID;
}

public void keyPressed(KeyEvent e) 
{ 
    System.out.println("keyPressed code : "+ e.getKeyCode());
    switch (e.getKeyCode()) 
    {
    case keys[KeyboardSettings.UP]:     gameBord.players[playerID].moveUp(); break;
    case keys[KeyboardSettings.DOWN]:   gameBord.players[playerID].moveDown(); break;   
    case keys[KeyboardSettings.LEFT]:   gameBord.players[playerID].moveLeft(); break;
    case keys[KeyboardSettings.RIGHT]:  gameBord.players[playerID].moveRight(); break;
    case keys[KeyboardSettings.BOMB]:   gameBord.players[playerID].addBomb(); break;

    default: gameBord.players[playerID].face = 0;
    }
    e.consume();

}

public void keyReleased(KeyEvent e) 
{
    System.out.println("keyReleased code : "+ e.getKeyCode());
    gameBord.players[playerID].move = false;
    gameBord.players[playerID].pic = 0;
    e.consume();
}

public void keyTyped(KeyEvent e) 
{
    System.out.println("keyTyped code : "+ e.getKeyCode());
    e.consume();
}

}

tnx ;)

Answer 1

Case expressions must be constant expressions.

You answered yourself in the title. You can't have a variable after case keyword.

The way how switch command works is that all the cases (the values after the case keyword) must be known in compile-time.

switch (e.getKeyCode()) {
    case constant1: commands;
    case constant2: commands;
}

keys[KeyboardSettings.UP] is not a constant, it is a variable. Its value is known in run-time. The compiler does not know what value is there and is shouting at you: "Hey, user3142930, I need to know the value of everything which follow the case keyword!"

In your case you simply cannot use switch. You should use a sequence of if-else commands, like this:

// store it in a variable so you do not call the method repeatedly
final int code = e.getKeyCode(); 
// this is instead of your switch
if (code == keys[KeyboardSettings.UP]) {
    ....
} 
else if (code == keys[KeyboardSettings.DOWN]) {
    ...
} 
else if (...) {
   ...
}

The deep reason for it is that you want to have the keys user-configurable, so you simply cannot know their values in compile-time.

You may study Runtime vs Compile time if you have not understood my last sentence.