Using keyboard to move circle at angles in java

Question

So, I have an application that successfully moves the ball (ellipse) left, right, up or down, depending on which button on the keyboard is pressed. However, I am having trouble getting the ball to move at an angle. I try to do this by saying that if the user holds 2 direction keys, the ball will go diagonally. For example, if they press the left key and the up key, I want the ball to move in the NorthWest direction. If any of you see the cause of the problem, I would be very grateful for your help!

Engine

class KeyClickListener implements KeyListener { public void keyPressed(KeyEvent e) { if (e.getKeyCode() == KeyEvent.VK_DOWN ) { component.moveCircle(1); } else if (e.getKeyCode() == KeyEvent.VK_UP) { component.moveCircle(2); } else if (e.getKeyCode() == KeyEvent.VK_RIGHT) { component.moveCircle(3); } else if (e.getKeyCode() == KeyEvent.VK_LEFT) { component.moveCircle(5); } //this is my attempt at telling whether or not the user was holding two keys else if (e.getKeyCode() == KeyEvent.VK_LEFT && e.getKeyCode() == KeyEvent.VK_UP) { component.moveCircle(5); } } public void keyReleased(KeyEvent e){} public void keyTyped(KeyEvent e){} } 

CircleComponent

  public void moveCircle(int w) { dir = w; if (dir == 1) { y+=20; repaint(); if (y>=560) { dir=2; } } . . . else if (dir == 5) { x-=10; y-=10; repaint(); if(x<=0 ) { dir=3; } } } 

Answer 1

Since key events will only report the last key that raised the event, your last if will never work, since keyCode will only match the last key that raised the event.

Instead, you should maintain the “state” of each key and handle this state instead.

 import java.awt.BorderLayout; import java.awt.Color; import java.awt.Dimension; import java.awt.EventQueue; import java.awt.FontMetrics; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.event.KeyAdapter; import java.awt.event.KeyEvent; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; public class TestKeyListener01 { public static void main(String[] args) { new TestKeyListener01(); } public TestKeyListener01() { EventQueue.invokeLater(new Runnable() { @Override public void run() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { } JFrame frame = new JFrame("Testing"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout()); frame.add(new TestPane()); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } }); } public class TestPane extends JPanel { private boolean arrowUp = false; private boolean arrowDown = false; private boolean arrowLeft = false; private boolean arrowRight = false; public TestPane() { setFocusable(true); addKeyListener(new KeyAdapter() { @Override public void keyReleased(KeyEvent e) { switch (e.getKeyCode()) { case KeyEvent.VK_DOWN: arrowDown = false; break; case KeyEvent.VK_UP: arrowUp = false; break; case KeyEvent.VK_LEFT: arrowLeft = false; break; case KeyEvent.VK_RIGHT: arrowRight = false; break; } repaint(); } @Override public void keyPressed(KeyEvent e) { switch (e.getKeyCode()) { case KeyEvent.VK_DOWN: arrowDown = true; break; case KeyEvent.VK_UP: arrowUp = true; break; case KeyEvent.VK_LEFT: arrowLeft = true; break; case KeyEvent.VK_RIGHT: arrowRight = true; break; } repaint(); } }); } @Override public Dimension getPreferredSize() { return new Dimension(200, 200); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g.create(); FontMetrics fm = g2d.getFontMetrics(); String text = "Up"; int x = (getWidth() - fm.stringWidth(text)) / 2; int y = ((getHeight() / 2) - fm.getHeight()); draw(g2d, text, x, y, arrowUp); text = "Down"; x = (getWidth() - fm.stringWidth(text)) / 2; y = ((getHeight() / 2) + fm.getHeight()) + fm.getAscent(); draw(g2d, text, x, y, arrowDown); text = "Left"; x = (getWidth() / 2) - fm.stringWidth(text) - 4; y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent(); draw(g2d, text, x, y, arrowLeft); text = "Right"; x = (getWidth() / 2) + 4; y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent(); draw(g2d, text, x, y, arrowRight); g2d.dispose(); } protected void draw(Graphics2D g2d, String text, int x, int y, boolean pressed) { g2d.setColor(pressed ? Color.BLACK : Color.GRAY); g2d.drawString(text, x, y); } } } 

I would also recommend using Key Bindings instead of KeyListener . They solve annoying focus problems that KeyListener KeyListener

Answer 2

Change your KeyClickListener and watch the magic! then check this out http://zetcode.com/tutorials/javagamestutorial/movingsprites/

  class KeyClickListener implements KeyListener, Runnable { private boolean moveLeft, moveRight, moveUp, moveDown; private Thread runThread; public KeyClickListener() { moveLeft = moveRight = moveUp = moveDown = false; runThread = new Thread(this); runThread.start(); } public void keyPressed(KeyEvent e) {assessKeycodes(e, true);} public void keyReleased(KeyEvent e){assessKeycodes(e, false);} public void keyTyped(KeyEvent e){} private void assessKeycodes(KeyEvent e, boolean setTo) { switch(e.getKeyCode()) { case KeyEvent.VK_DOWN: moveDown = setTo; break; case KeyEvent.VK_UP: moveDown = setTo; break; case KeyEvent.VK_LEFT: moveDown = setTo; break; case KeyEvent.VK_RIGHT: moveDown = setTo; break; } } public void run() { while(true) { if (moveDown) component.moveCircle(1); if (moveUp) component.moveCircle(2); if (moveRight) component.moveCircle(3); if (moveLeft) component.moveCircle(5); } } }