Question

I have a specialized frame class and a specialized panel class. I have a keylistener setup to listen for key presses of the “right” key (->)and then I call repaint but nothing happens when I press the “right” key. I believe my keylistener is done properly so I think it must be the way I call repaint(); Let me know how to fix this please.

Edit* I would like to add that I made x and y in CircleFrame static because I couldn’t find a way to call the incX() and incY() methods I had written. This was because, originally, the creation of the panel was done in the constructor for CircleBox. I took that out and put it in main in order to have a way to call repaint() for the panel but that didn’t work. I feel like theres some vital step im missing here.

package circlebox;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.Random;

public class CircleBox extends JFrame implements KeyListener {
    CircleBox() {

    }

    public void keyPressed(KeyEvent e) {
        int location = e.getKeyLocation();
        if(location == KeyEvent.KEY_LOCATION_NUMPAD) {
            CircleFrame.y += 1;
            repaint();
        }
    }

    public void keyReleased(KeyEvent e) {

    }

    public void keyTyped(KeyEvent e) {

    }

    public static void main(String[] args) {
        CircleBox frame = new CircleBox();
        frame.setSize(400,400);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        CircleFrame frame2 = new CircleFrame();
        frame.setLayout(new GridLayout(1,1));
        frame.add(frame2);

        frame.setVisible(true);
    }
}

class CircleFrame extends JPanel {
    static int x = 20;
    static int y = 20;
    int radius = 20;

    CircleFrame() {
        setSize(400,400);
    }

    @Override
    protected void paintComponent(Graphics g) {
        g.drawOval(x,y,radius,radius);
    }

    public void incX(int inc) {
        x += inc;
    }

    public void incY(int inc) {
        y += inc;
    }

    public int checkCollisions() {
        if(x <= 0) {
            return 0;
        }
        else if(y <= 0) {
            return 1;
        }
        else if(x >= 400) {
            return 2;
        }
        else if(y >= 400) {
            return 3;
        }
        else {
            return -1;
        }
    }
}

Answer 1

Your repaint is working just fine. The problem is with the key listener.

You first need to actually register your key listener. So, add this line in the CircleBox constructor:

addKeyListener(this);

Then, you must handle the keyPressed correctly:

public void keyPressed(KeyEvent e) {
    // TODO: your are actually moving the circle down, so it should be VK_DOWN
    if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
        CircleFrame.y += 1;
        repaint();
    }
}