private void checkInput() {
        switch(state) {
        case INTRO:
            if(Keyboard.isKeyDown(Keyboard.KEY_RETURN)) {
                state = State.MAIN_MENU;
            }
            if(Keyboard.isKeyDown(Keyboard.KEY_ESCAPE)) {
                Display.destroy();
                System.exit(0);
            }
            break;
        case MAIN_MENU:
            if(Keyboard.isKeyDown(Keyboard.KEY_RETURN)) {
                state = State.GAME;
            }
            if(Keyboard.isKeyDown(Keyboard.KEY_SPACE)) {
                state = State.INTRO;
            }
            break;
        case GAME:
            if(Keyboard.isKeyDown(Keyboard.KEY_BACK)) {
                state = State.MAIN_MENU;
            }
            break;
        }
    }