报screen exception:java.lang installexception:class not a midlet异常
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报screen exception:java.lang installexception:class not a midlet异常? 原码如下：
? import javax.microedition.lcdui.*;
? //import javax.microedition.midlet.*;
?
? public class screen extends Canvas implements Runnable , CommandListener
? {
? Command start=new Command("start",Command.OK,1);
? Command stop=new Command("stop",Command.STOP,1);
? private Image offscreen;
? public screen() {
?
? addCommand(start);
? addCommand(stop);
? if (isDoubleBuffered())
? {
? System.out.println("mutable");
? }
? else
? { System.out.println("immutable");
? offscreen=Image.createImage(getWidth(),getHeight());
?
? }// TODO Auto-generated constructor stub
? }
? public void paint(Graphics g){
? if(isDoubleBuffered())
? {
? System.out.println("on-screen");
? clear(g);
? paintAnimation(g,100,10,r);
? paintCross(g,x,y,length);
? }
? else
? {
? System.out.println("off-screen");
? Graphics offs=offscreen.getGraphics();
? clear(offs);
? paintAnimation(offs,100,10,r);
? paintCross(offs,x,y,length);
? g.drawImage(offscreen,0,0,0);
? }
? }
? public void clear(Graphics g){
? g.setColor(255,255,55);
? g.fillRect(0,0,getWidth(),getHeight());
? }
? int r=0;
? public void paintAnimation(Graphics g,int x,int y,int l){
? g.setColor(255,255,0);
? g.drawLine(x-length,y,x+length,y);
? g.drawLine(x,y-length,x,y+length);
? }
? boolean conti=false;
? int x=50;
? int y=50;
? int length=5;
? public void paintCross(Graphics g,int x,int y ,int length){
? g.setColor(255,0,0);
? g.drawLine(x-length,y,x+length,y);
? g.drawLine(x,y-length,x,y+length);
?
? }
? public void commandAction(Command c,Displayable s){
? String cmd=c.getLabel();
? if(cmd.equals("stop"))
? {
? conti=false;
? removeCommand(stop);
? addCommand(start);
? }
? else if(cmd.equals("start"))
? {
? removeCommand(start);
? addCommand(stop);
? conti=true;
? Thread t=new Thread(this);
? t.start();
?
? }
? }
? int rate=50;
? public void run(){
? long s=0;
? long e=0;
? long diff=0;
? while(conti){
? s=System.currentTimeMillis();
? r++;
? if(r>10)
? r=0;
? repaint();
? serviceRepaints();
? e=System.currentTimeMillis();
? diff=e-s;
? if(diff<rate)
? try{
? Thread.sleep(rate-diff);
? }catch(Exception exc){}
