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POHow to extend this class and use it in my Java applet? I get NullPointerException
 

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  1. POHow to extend this class and use it in my Java applet? I get NullPointerException
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    <p>I found the below code here: <a href="https://stackoverflow.com/questions/2873506/how-to-use-double-buffering-inside-a-thread-and-applet">How to use double buffering inside a thread and applet</a></p> <p>It says "extend AppletGameCore and define your own subclass that implements the required methods." Can someone please show me how you might do this so that I can use double buffering in my applet?</p> <pre><code>import java.awt.Canvas; import java.awt.Graphics2D; import java.awt.Dimension; import java.awt.image.BufferStrategy; import java.applet.Applet; /** *AppletGameCore.java *@author David Graham */ public abstract class AppletGameCore extends Applet implements Runnable { private BufferStrategy bufferStrategy; private Canvas drawArea;/*Drawing Canvas*/ private boolean stopped = false;/*True if the applet has been destroyed*/ private int x = 0; public void init() { Thread t = new Thread(this); drawArea = new Canvas(); setIgnoreRepaint(true); t.start(); } public void destroy() { stopped = true; /*Allow Applet to destroy any resources used by this applet*/ super.destroy(); } public void update() { if(!bufferStrategy.contentsLost()) { //Show bufferStrategy bufferStrategy.show(); } } //Return drawArea's BufferStrategy public BufferStrategy getBufferStrategy() { return bufferStrategy; } //Create drawArea's BufferStrategies public void createBufferStrategy(int numBuffers) { drawArea.createBufferStrategy(numBuffers); } //Subclasses should override this method to do any drawing public abstract void draw(Graphics2D g); public void update(Graphics2D g) { g.setColor(g.getBackground()); g.fillRect(0,0,getWidth(),getHeight()); } //Update any sprites, images, or primitives public abstract void update(long time); public Graphics2D getGraphics() { return (Graphics2D)bufferStrategy.getDrawGraphics(); } //Do not override this method public void run() { drawArea.setSize(new Dimension(getWidth(),getHeight())); add(drawArea); createBufferStrategy(2); bufferStrategy = drawArea.getBufferStrategy(); long startTime = System.currentTimeMillis(); long currTime = startTime; //animation loop while(!stopped) { //Get time past long elapsedTime = System.currentTimeMillis()-currTime; currTime += elapsedTime; //Flip or show the back buffer update(); //Update any sprites or other graphical objects update(elapsedTime); //Handle Drawing Graphics2D g = getGraphics(); update(g); draw(g); //Dispose of graphics context g.dispose(); } } } </code></pre> <p>Below is my attempt. I get the error: java.lang.NullPointerException at AppletGameCore.run(AppletGameCore.java:76) at ExtendTest.init(ExtendTest.java:10) at sun.applet.AppletPanel.run(Unknown Source) at java.lang.Thread.run(Unknown Source)</p> <pre><code>import java.awt.Canvas; import java.awt.Graphics2D; import java.awt.Dimension; import java.awt.image.BufferStrategy; import java.applet.Applet; public class ExtendTest extends AppletGameCore { public void init() { setSize(420, 420); run(); } public void draw(Graphics2D g) {} public void update(long l) {} } </code></pre>
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