Question

I’m still very new to Java and I have the following problem.
As you can see below I’ve created a JPanel with an image that I want to change whenever I click on the panel, but It doesn’t work for some reason. I’ve been sitting on it for hours now and seem to be completely stuck. If you could take a look at the code and help me I would be very grateful.
Thank you and have a nice Christmas.

public class Level {
  JPanel panel
  String img1Path = "img1.png";
  String img2Path = "img2.png";
  Image img1 = Toolkit.getDefaultToolkit().getImage(img1Path);
  Image img2 = Toolkit.getDefaultToolkit().getImage(img2Path);
  boolean s1 = false;

  public Level(){
    initGUI();
  }

  public void initGUI(){
    panel = new JPanel(){
      public void paintComponent(Graphics g){
       super.paintComponent(g);
       draw(g,s1);
      }
    }
   panel.addMouseListener(new ImgListener(s1));
  }

  public void draw(Graphics g, boolean s){
    if(s==true){
      g.drawImage(img1,0,0,this);}
    else if(s==false){
      g.drawImage(img2,0,0,this);}
    }//draw()

  public void click(boolean s, boolean b){
    s = b;
    repaint();
  }

  public class ImgListener extends MouseAdapter {
    boolean s;

    public ImgListener(boolean s){
      pS(s);
    }

    public void mouseClicked(MouseEvent e){
      if(s==true){
        click(s,false);
      }
      else if(s==false){
        click(s,true);
      }
   }//mouseClicked

  public void pS(boolean s){
    this.s = s;
   }//pS

  }//ImgListener

}//Level

Answer 1

Java is pass-by-value always, and so your click method will not change your class’s boolean field:

public void click(boolean s, boolean b){
  s = b;  // this does not change the class field s.
  repaint();
}

The reason is the s parameter above is not the same as the class’s s field, but instead the parameter does what is known as “shadows” the class field. A solution is to change this method and get rid of the s parameter. Or better — get rid of the method entirely.

Note that if this were my application, I’d use a JLabel, give it a MouseListener, and simply swap ImageIcons on mousePressed.

Also your boolean toggle method:

public void mouseClicked(MouseEvent e){
  if(s==true){
    click(s,false); 
  }
  else if(s==false){
    click(s,true);
  }
}

can be greatly simplified and corrected by doing this and getting rid of the erroneous click(…) method:

public void mouseClicked(MouseEvent e){
  s = !s;
  repaint();
}

As an aside, if (s == true) is unnecessarily redundant. If you need a construct like this, you can more succinctly and simply do if (s). Same for if (s == false) which is better represented as if (!s)