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Skipping and breaking in Java animation

The following code draws a square with two smaller squares rotating inside it. whenever you press the arrow on the keyboard, the whole system will move in that direction. however, I have problems with tearing the image and sometimes miss (its small, but still there). I was wondering if anyone knows how I can fix these problems without mass code changes.

import java.awt.*; import java.awt.event.*; import javax.swing.*; import static java.awt.Color.*; public class GUI extends JPanel implements ActionListener, KeyListener { int x, y, x1, y1, x2, y2, changeX, changeY, changeX2, changeY2; JFrame frame; Runtime r; public static void main(String[] args) { new GUI(); } public GUI() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (Exception e) { e.printStackTrace(); } setSize(1020,770); setBackground(WHITE); setOpaque(true); setVisible(true); x = 0; y = 0; x1 = 0; y1 = 0; x2 = 0; y2 = 0; changeX=1; changeY=0; changeX2=1; changeY2=0; r = Runtime.getRuntime(); frame = new JFrame(); frame.setSize(1020,819); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setJMenuBar(createMenuBar()); frame.validate(); frame.setBackground(WHITE); frame.addKeyListener(this); frame.setTitle("GUI"); frame.setContentPane(this); frame.setVisible(true); frame.createBufferStrategy(2); Timer t = new Timer(100,this); t.setActionCommand("Draw"); t.start(); repaint(); } public JMenuBar createMenuBar() { JMenuBar menuBar = new JMenuBar(); JMenu fileMenu = new JMenu("File"); JMenuItem save = new JMenuItem("Save"); save.setMnemonic(KeyEvent.VK_S); save.setContentAreaFilled(false); save.setOpaque(false); save.addActionListener(this); JMenuItem load = new JMenuItem("Load"); load.setMnemonic(KeyEvent.VK_L); load.setContentAreaFilled(false); load.setOpaque(false); load.addActionListener(this); JMenuItem quit = new JMenuItem("Quit"); quit.setMnemonic(KeyEvent.VK_Q); quit.setContentAreaFilled(false); quit.setOpaque(false); quit.addActionListener(this); fileMenu.add(save); fileMenu.add(load); fileMenu.addSeparator(); fileMenu.add(quit); fileMenu.setContentAreaFilled(false); fileMenu.setBorderPainted(false); fileMenu.setOpaque(false); JMenu editMenu = new JMenu("Edit"); JMenuItem undo = new JMenuItem("Undo"); undo.setMnemonic(KeyEvent.VK_U); undo.setContentAreaFilled(false); undo.setOpaque(false); undo.addActionListener(this); JMenuItem redo = new JMenuItem("Redo"); redo.setMnemonic(KeyEvent.VK_R); redo.setContentAreaFilled(false); redo.setOpaque(false); redo.addActionListener(this); editMenu.add(undo); editMenu.add(redo); editMenu.setContentAreaFilled(false); editMenu.setBorderPainted(false); editMenu.setOpaque(false); JMenu helpMenu = new JMenu("Help"); JMenuItem controls = new JMenuItem("Controls"); controls.setMnemonic(KeyEvent.VK_C); controls.setContentAreaFilled(false); controls.setOpaque(false); controls.addActionListener(this); JMenuItem about = new JMenuItem("About"); about.setMnemonic(KeyEvent.VK_A); about.setContentAreaFilled(false); about.setOpaque(false); about.addActionListener(this); helpMenu.add(controls); helpMenu.addSeparator(); helpMenu.add(about); helpMenu.setContentAreaFilled(false); helpMenu.setBorderPainted(false); helpMenu.setOpaque(false); menuBar.add(fileMenu); menuBar.add(editMenu); menuBar.add(helpMenu); return menuBar; } public void paintComponent(Graphics g) { g.clearRect(0, 0, 1020, 770); g.setColor(BLACK); g.fillRect(x,y,100,100); g.setColor(RED); g.fillRect(x1,y1,50,50); g.setColor(BLUE); g.fillRect(x2,y2,25,25); g.dispose(); } public void change() { if(x1>=x+50&&changeY==0&&changeX==1) { changeX=0; changeY=1; } else if(y1>=y+50&&changeX==0&&changeY==1) { changeX=-1; changeY=0; } else if(x1<=x&&changeX==-1&&changeY==0) { changeX=0; changeY=-1; } else if(y1<=y&&changeY==-1&&changeX==0) { changeX=1; changeY=0; } x1+=changeX*5; y1+=changeY*5; } public void change2() { if(x2>=x1+25&&changeY2==0&&changeX2==1) { changeX2=0; changeY2=1; } else if(y2>=y1+25&&changeX2==0&&changeY2==1) { changeX2=-1; changeY2=0; } else if(x2<=x1&&changeX2==-1&&changeY2==0) { changeX2=0; changeY2=-1; } else if(y2<=y1&&changeY2==-1&&changeX2==0) { changeX2=1; changeY2=0; } x2+=changeX2*2; y2+=changeY2*2; } public void actionPerformed(ActionEvent e) { if(e.getActionCommand().equalsIgnoreCase("Draw")) { r.runFinalization(); r.gc(); change(); change2(); repaint(); } } public void keyPressed(KeyEvent e) { if(e.getKeyCode()==KeyEvent.VK_UP) { if(y-10>=0) { y-=10; y1-=10; y2-=10; } } if(e.getKeyCode()==KeyEvent.VK_DOWN) { if(y+110<=getHeight()) { y+=10; y1+=10; y2+=10; } } if(e.getKeyCode()==KeyEvent.VK_LEFT) { if(x-10>=0) { x-=10; x1-=10; x2-=10; } } if(e.getKeyCode()==KeyEvent.VK_RIGHT) { if(x+110<=getWidth()) { x+=10; x1+=10; x2+=10; } } repaint(); } public void keyReleased(KeyEvent e) { } public void keyTyped(KeyEvent e) { } }
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2 answers

You do not build on EDT . The javax.swing.Timer instance makes this easier since the action event handler is executed on the EDT .

Appendix 1: you may decide that you need double buffering , but first compare the code below with yours and see. If you go along this route, you can see this tutorial .

Addendum 2: The example below shows how to maintain an off-screen buffer, but it is sometimes easier to use the JPanel(boolean isDoubleBuffered) constructor JPanel(boolean isDoubleBuffered) for a similar effect.

 import java.awt.event.KeyAdapter; import java.awt.Dimension; import java.awt.EventQueue; import java.awt.Graphics; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.KeyEvent; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.Timer; import static java.awt.Color.*; /** @see http://stackoverflow.com/questions/2114455 */ public class GUI extends JPanel implements ActionListener { int x, y, x1, y1, x2, y2, changeY, changeY2; int changeX = 1; int changeX2 = 1; Timer t = new Timer(100, this); public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { @Override public void run() { new GUI(true).display(); } }); } public GUI(boolean doubleBuffered) { super(doubleBuffered); this.setPreferredSize(new Dimension(320, 240)); } private void display() { JFrame frame = new JFrame("GUI"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.addKeyListener(new KeyListener()); frame.add(this); frame.pack(); frame.setVisible(true); t.start(); } @Override public void paintComponent(Graphics g) { g.setColor(WHITE); g.fillRect(0, 0, getWidth(), getHeight()); g.setColor(BLACK); g.fillRect(x, y, 100, 100); g.setColor(RED); g.fillRect(x1, y1, 50, 50); g.setColor(BLUE); g.fillRect(x2, y2, 25, 25); } public void change() { if (x1 >= x + 50 && changeY == 0 && changeX == 1) { changeX = 0; changeY = 1; } else if (y1 >= y + 50 && changeX == 0 && changeY == 1) { changeX = -1; changeY = 0; } else if (x1 <= x && changeX == -1 && changeY == 0) { changeX = 0; changeY = -1; } else if (y1 <= y && changeY == -1 && changeX == 0) { changeX = 1; changeY = 0; } x1 += changeX * 5; y1 += changeY * 5; } public void change2() { if (x2 >= x1 + 25 && changeY2 == 0 && changeX2 == 1) { changeX2 = 0; changeY2 = 1; } else if (y2 >= y1 + 25 && changeX2 == 0 && changeY2 == 1) { changeX2 = -1; changeY2 = 0; } else if (x2 <= x1 && changeX2 == -1 && changeY2 == 0) { changeX2 = 0; changeY2 = -1; } else if (y2 <= y1 && changeY2 == -1 && changeX2 == 0) { changeX2 = 1; changeY2 = 0; } x2 += changeX2 * 2; y2 += changeY2 * 2; } @Override public void actionPerformed(ActionEvent e) { change(); change2(); repaint(); } private class KeyListener extends KeyAdapter { @Override public void keyPressed(KeyEvent e) { int d = 5; if (e.getKeyCode() == KeyEvent.VK_UP) { if (y - d >= 0) { y -= d; y1 -= d; y2 -= d; } } if (e.getKeyCode() == KeyEvent.VK_DOWN) { if (y + 100 + d <= getHeight()) { y += d; y1 += d; y2 += d; } } if (e.getKeyCode() == KeyEvent.VK_LEFT) { if (x - d >= 0) { x -= d; x1 -= d; x2 -= d; } } if (e.getKeyCode() == KeyEvent.VK_RIGHT) { if (x + 100 + d <= getWidth()) { x += d; x1 += d; x2 += d; } } } } }
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I would look at double buffering. Basically, you draw on the on-screen graphic and then draw an off-screen graphic on the JPanel.

~ Bolt

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