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PODetect overlapping objects in java Swing
 

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  1. PODetect overlapping objects in java Swing
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    <p>I am trying to make a program that has a moving ball and a platform that it will sit on. I am new too java and I cant figure out how to detect when 2 swing objects are overlapping. My code it below and I am wondering what the best way is to detect overlapping objects.</p> <p>KeyDemo.java:</p> <pre><code> import javax.swing.*; import java.awt.*; import java.awt.event.*; public class KeyDemo { public static void main(String[] args) { JFrame frame = new JFrame(); JPanel panel = new JPanel(); LayoutManager overlay = new OverlayLayout(panel); panel.setLayout(overlay); 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(); } } </code></pre> <p>KeyboardController.java:</p> <pre><code> import java.awt.*; import java.awt.event.*; 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) { } } </code></pre> <p>BallComponent.java:</p> <pre><code> import javax.swing.*; import java.awt.*; import java.awt.event.*; import java.awt.geom.*; public class BallComponent extends JComponent { int xSpeed; int ySpeed; int x; int y; public BallComponent(int x, int y) { super(); this.x = x; this.y = y; } public void paintComponent(Graphics g) { Graphics2D g2 = (Graphics2D)g; Ellipse2D.Double ball = new Ellipse2D.Double(x-10,y-10,10,10); 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() { x=x+xSpeed; y=y+ySpeed; repaint(); } public void stopY() { ySpeed=0; } public void stopX() { xSpeed=0; } } </code></pre> <p>WallComponent.java:</p> <pre><code> import javax.swing.*; import java.awt.*; import java.awt.event.*; import java.awt.geom.*; public class WallComponent extends JComponent { int x; int y; public WallComponent(int x, int y) { super(); this.x = x; this.y = y; } public void paintComponent(Graphics g) { Graphics2D g2 = (Graphics2D)g; Rectangle wall = new Rectangle(x-40,y-40,40,40); g2.setColor(Color.YELLOW); g2.fill(wall); g2.draw(wall); } public void checkOverlap(BallComponent bc){ if (this.contains(bc.getLocation())){ bc.stopY(); bc.stopX(); } } } </code></pre>
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    1. COStart by making sure you are calling `super.paintComponent` before you perform your custom painting, especially when extending from `JComponent`
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    2. CODon't use `magic numbers`. Nobody know what 37, 38, 39 and 40 mean. Read the KeyEvent API for the proper variable names to use (KeyEvent.VK_RIGHT...). Better yet don't even use a KeyListener. See [Motion Using the Keyboard]() for a better approach that uses `Key Bindings`.
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      1. UScamickr
 

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