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copied!<p>All Swing components have a concept of "bounds". This is a rectangular area within which they are "drawn".</p> <p>If you are controlling the size and position correctly, you should be able to use the <code>contains</code> method of the <code>Rectangle</code> which is returned from calling <a href="http://docs.oracle.com/javase/7/docs/api/java/awt/Component.html#getBounds%28%29" rel="nofollow"><code>Component#getBounds</code></a></p> <p>So you <code>checkOverlap</code> method could look like...</p> <pre><code>public void checkOverlap(BallComponent bc){ if (getBounds().intersects(bc.getBounds())){ bc.stopY(); bc.stopX(); } } </code></pre> <p>You will also want to make sure that you are calling <code>super.paintComponent</code> before performing any custom painting, espeically when using components that extend from <code>JComponent</code>. This will ensure that the <code>Graphics</code> context is prepared for painting correctly...</p> <p><strong>Updated</strong></p> <p>There's a cascade of issues. Basically, instead of positing the components within the parent container yourself (which is how I thought you had done it), you've laid each component out to fill the parent container and only "painted" the objects...This makes life more difficult</p> <p>Instead, if you are going to use components, I would use a <code>null</code> layout (or even possibly use a <code>JLayeredPane</code> as the parent container).</p> <p>I would then change the physical position of the components, for example...</p> <pre><code>import java.awt.Color; import java.awt.EventQueue; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.LayoutManager; import java.awt.Rectangle; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.KeyEvent; import java.awt.event.KeyListener; import java.awt.geom.Ellipse2D; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.OverlayLayout; import javax.swing.Timer; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; public class TestGame { public static void main(String[] args) { new TestGame(); } public TestGame() { EventQueue.invokeLater(new Runnable() { @Override public void run() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { } JFrame frame = new JFrame(); JPanel panel = new JPanel(); panel.setLayout(null); final int FRAME_WIDTH = 800; final int FRAME_HEIGHT = 600; frame.setSize(FRAME_WIDTH, FRAME_HEIGHT); frame.setTitle("Move the Ball"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); final WallComponent wc1 = new WallComponent(400, 400); final BallComponent bc = new BallComponent(400, 300); panel.add(wc1); panel.add(bc); frame.add(panel); KeyboardController kc = new KeyboardController(bc); frame.addKeyListener(kc); frame.setVisible(true); class AnimationListener implements ActionListener { public void actionPerformed(ActionEvent event) { bc.tick(); wc1.checkOverlap(bc); } } ActionListener aListener = new AnimationListener(); final Timer timer = new Timer(1, aListener); timer.start(); } }); } public class KeyboardController implements KeyListener { BallComponent bComp; public KeyboardController(BallComponent t) { bComp = t; } /** * Handle the key pressed event from the text field. */ public void keyPressed(KeyEvent e) { int keyCode = e.getKeyCode(); if (keyCode == 38) { System.out.println("Pressed Up!"); bComp.moveUp(); } if (keyCode == 37) { System.out.println("Pressed Left!"); bComp.moveLeft(); } if (keyCode == 39) { System.out.println("Pressed Right!"); bComp.moveRight(); } if (keyCode == 40) { System.out.println("Pressed Down!"); bComp.moveDown(); } } /** * Handle the key released event from the text field. */ public void keyReleased(KeyEvent e) { int keyCode = e.getKeyCode(); if (keyCode == 38) { System.out.println("Released Up!"); bComp.stopY(); } if (keyCode == 37) { System.out.println("Released Left!"); bComp.stopX(); } if (keyCode == 39) { System.out.println("Released Right!"); bComp.stopX(); } if (keyCode == 40) { System.out.println("Pressed Down!"); bComp.stopY(); } } public void keyTyped(KeyEvent e) { } } public class BallComponent extends JComponent { int xSpeed; int ySpeed; public BallComponent(int x, int y) { super(); setBounds(x, y, 10, 10); } public void paintComponent(Graphics g) { Graphics2D g2 = (Graphics2D) g; Ellipse2D.Double ball = new Ellipse2D.Double(0, 0, 9, 9); g2.setColor(Color.RED); g2.fill(ball); g2.draw(ball); } public void moveLeft() { xSpeed = -1; } public void moveRight() { xSpeed = 1; } public void moveUp() { ySpeed = -1; } public void moveDown() { ySpeed = 1; } public void tick() { int x = getX() + xSpeed; int y = getY() + ySpeed; setLocation(x, y); repaint(); } public void stopY() { ySpeed = 0; } public void stopX() { xSpeed = 0; } } public class WallComponent extends JComponent { public WallComponent(int x, int y) { super(); setBounds(x, y, 40, 40); } public void paintComponent(Graphics g) { Graphics2D g2 = (Graphics2D) g; Rectangle wall = new Rectangle(0, 0, 40, 40); g2.setColor(Color.YELLOW); g2.fill(wall); g2.draw(wall); } public void checkOverlap(BallComponent bc) { System.out.println(" me: " + getBounds()); System.out.println("you: " + bc.getBounds()); if (getBounds().intersects(bc.getBounds())) { bc.stopY(); bc.stopX(); } } } } </code></pre> <p>Now, you could use "painted" objects, but in that case I would have a virtual concept of a <code>Ball</code> and <code>Wall</code> which you could paint within a single component. These objects would need to provide information about there position and size, which you could, again, check using <code>Rectangle#intersects</code>...</p>

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