Key Listener Null Pointer Exception

Question

I am beginner in Java. I am trying to make a gui game and I want to add key adapter but I dont know where should i get as parameter start- where is Jframe extended Slides-where is new Layout set (panels buttons etc) Casual - where is setText change

I use many seperate class like Colors and Fonts but I think that I dont have to include that.

Here is a two fragments that throws Null Pointer Exception. I must add I tried all classes above as parameter to constructor but it didnt worked .After all here is code :

Casual.java (fragment)

            public void firstDay(){
            pv.movingHandlerON=true;
            start.addKeyListener(new MovingChoiceHandler(slides)); // naprawic !
            music.setMusic(pv.musicDay);
            music.loopMusic(99);
            music.startMusic();
             slides.textPanel.setText("You had the accident in forrest.\nYou take all u got and go 
            into adventure.\n\nWhere do You want to go?\n\n[Q] Go forest Pathway  [Z] Go Muddy 
             road");
    
       }

MovingChoiceHandler .java (full code without import and package)

          public class MovingChoiceHandler extends KeyAdapter {
        PlayerVariables pv=new PlayerVariables();
        Start start;
        Slides slides;
        Casual casual;
    
    
        MovingChoiceHandler(Slides slides){
    this.start=slides.start;
    
    
        }
    
    
    // tutaj przez strzałki bedziemy zmieniac slajdy
        public void keyPressed(KeyEvent e){
          //  if(pv.movingHandlerON==true) {
                switch (e.getKeyCode()) {
    
                    case KeyEvent.VK_Q:
                        System.out.println("Sprawdzanie gory check");
                        break;
    
    
                    case KeyEvent.VK_W:
                        System.out.println("Sprawdzanie dolu check");
                        break;
    
    
                }
            //}
        }
    
    
    }

If You interested more here it is full code if You dont see here any problem. As I say i tried start, casual,and slides but it still throw this exception.I tried even like

this.slides=slides;

this.start=slides.start;

Full code :

Start.java : https://pastebin.com/tmv7td8x

StartButtonHandler (start->slides) :https://pastebin.com/3ZX1CZgT

Slides.java :https://pastebin.com/bebR4qBk (Casual is added without handler into Slides)

Casual.java :https://pastebin.com/mR1DS1cJ

MovingChoiceHandler.java: https://pastebin.com/rXtSkN4c

(added in first method in casual to change next "slides"

Does [this](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) answer your question? — JustAnotherDeveloper, Sep 06 '20 at 13:42

score 0 · Answer 1 · answered Sep 06 '20 at 13:49

Back then in Slides i send new Casual(start) even that i recived start in this class.So i fixed it and set is as

new Casual(this);

and in Casual:

Casual(Slides slides){

this.slides=slides;
this.start=slides.start;
 }

and under also i set

start.addKeyListener(new MovingChoiceHandler(slides));

And in moving choice handler i set :

            MovingChoiceHandler(Slides slides){
                 this.slides=slides;
                 this.start=slides.start;
        }

And it works :)

Key Listener Null Pointer Exception

1 Answers1