Java StackOverflowException in GUI

Question

so I have this little snake game and I get StackOverflow error which looks like so:

 Exception in thread "main" java.lang.StackOverflowError
at java.awt.Component.setBackground(Component.java:1835)
at javax.swing.JComponent.setBackground(JComponent.java:2733)
at javax.swing.LookAndFeel.installColors(LookAndFeel.java:175)
at javax.swing.LookAndFeel.installColorsAndFont(LookAndFeel.java:211)
at javax.swing.plaf.basic.BasicPanelUI.installDefaults(BasicPanelUI.java:66)
at javax.swing.plaf.basic.BasicPanelUI.installUI(BasicPanelUI.java:56)
at javax.swing.JComponent.setUI(JComponent.java:666)
at javax.swing.JPanel.setUI(JPanel.java:153)
at javax.swing.JPanel.updateUI(JPanel.java:126)
at javax.swing.JPanel.<init>(JPanel.java:86)
at javax.swing.JPanel.<init>(JPanel.java:109)
at javax.swing.JPanel.<init>(JPanel.java:117)
at SnakeGame.Animation.<init>(Animation.java:36)
at SnakeGame.Snake.<init>(Snake.java:24)
at SnakeGame.Animation.<init>(Animation.java:38)
at SnakeGame.Snake.<init>(Snake.java:24)

I know there's some infinite recursion going on but I don't get it. It seems like just a constructor. so Here's code for Animation class:

//imports are there
interface Drawable{
public void draw(Graphics g);
}


public class Animation extends JPanel implements ActionListener,   KeyListener{

JFrame frame;
List <Drawable> toDraw;
Snake snake;
Food food;
Timer timer;

public static boolean gameOver = false;
public static int UNIT = 20;
public static int SIZE = 500;


public static void main(String[] args){
   Animation animate = new Animation();
   animate.setUpFrame();
}

Animation(){

    toDraw = new ArrayList<>(); // this is line 38 from exception
    snake = new Snake(SIZE/2,SIZE/2);
    food = new Food();
    toDraw.add(snake);
    toDraw.add(food);
    initTimer();
}

void initTimer(){
    timer = new Timer(200, this);
    timer.setInitialDelay(1000);
    timer.start();
}

void setUpFrame(){
    frame = new JFrame("Snake");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(SIZE, SIZE);
    frame.setFocusable(true);
    frame.setVisible(true);
    frame.add(this);
}

void gameRun() {
       //haven't written here anything yet.  
}  

   @Override
public void paintComponent(Graphics g){
    super.paintComponent(g);
    this.setBackground(new Color(70,130,80));

    for(Drawable d : toDraw){
        d.draw(g);
    }  

}

@Override
public void actionPerformed(ActionEvent e) {
        gameRun();
        repaint();
}


@Override
public void keyTyped(KeyEvent e) {

}

@Override
public void keyPressed(KeyEvent e) {
    int c = e.getKeyCode();
    switch(c){
        case 'L':
           snake.setDirection('L');
            break;
        case 'R':
            snake.setDirection('R');         
            break;
        case 'U':
            snake.setDirection('U');
            break;
        case 'D':
            snake.setDirection('D');
            break;
    }
}

@Override
public void keyReleased(KeyEvent e) {

}

}

And here's snake class:

   public class Snake extends Animation implements Drawable {

int x;
int y;
char direction = 'N';

Snake(int x, int y){ //line 24 from exception
    this.x = x;
    this.y = y;
}


void setDirection(char way){
    direction = way;
}
void move(char direction){

    if(x < 0){
      x = SIZE;  
    } 
    else if(x > SIZE){
        x = 0;
    }
    if(y < 0){
        y= SIZE;
    }else if (y > SIZE){
        y = 0;
    }

    switch(direction){
        case 'L':
            x-= UNIT;
            break;
        case 'R':
            x+= UNIT;              
            break;
        case 'U':
            y-= UNIT;    
            break;
        case 'D':
            y+= UNIT;
            break;
    }  
}

@Override
public void draw(Graphics g) {
    g.setColor(new Color(160,2,42));
    g.fill3DRect(x, y, UNIT, UNIT, true);
  }  
}

Any help would be greatly appreciated!

Your inheritance makes no sense, why does Snake extend Animation in the first place anyways? — Andrew Li
– Andrew Li, Commented Nov 27, 2016 at 19:08
@AndrewLi Thanks got it! inheritance is my weak spot. I think I'll just create abstract class for any physical object and extend off of it. — Grigory Bogush
– Grigory Bogush, Commented Nov 27, 2016 at 19:16

Hovercraft Full Of Eels · Accepted Answer · 2016-11-27 19:04:06Z

2

You've got unintended recursion due to your program's inheritance structure:

Your Snake extends Animation which creates a Snake in its constructor which extends Animation which creates a Snake in its constructor which extends Animation which creates a Snake in its constructor which extends Animation which creates a Snake in its constructor which extends Animation which creates a Snake in its constructor ... etc...

Solution: don't have Snake extend Animation. And this also makes logical sense, since your Snake is not acting as a Swing component such as a JPanel, and so shouldn't inherit from JPanel. Rather it's a logical entity that is drawn by the JPanel -- and so you want to use composition here (which you're already doing) and not inheritance (which you're unfortunately doing as well).

answered Nov 27, 2016 at 19:04

Hovercraft Full Of Eels

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1 Comment

Grigory Bogush Over a year ago

Thank you! I don't know how inheritance works very well since I read about it at the time when I couldn't do anything in java. I need to refresh my knowledge.

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