关于J2ME低级界面和高级界面跳转死机问题！！十万火急！！！高手帮忙！！！

最近写了一个小软件，在模拟器上运行的时候一点事都没有，一切正常，放到手机上就有问题了，问题如下：
由于牵扯到发短信，需要由低级界面跳转到高级界面，由低跳高是正常，短信能发出去，发完要由高级跳回低级界面是出问题了，当跳回低级界面是就死机了，死在低级界面上了，按什么都没反应，只能关机重启手机，很郁闷。开始以为是内存爆了，内存溢出，可是也System.gc()了，该null的地方也null了，还是这问题。后来发现就是在界面跳转的时候死机的，各位高人，知不知道低级界面和高级界面之间跳转都有什么注意的，不小心会出什么问题，我这样的情况怎么解决！
重谢！！！！！！！代码如下：
public PoemCanvas(PoemMidlet midlet) {
logoi = 0;
g = null;
setFullScreenMode(true);
this.midlet = midlet;
canvasWidth = 176;
canvasHeight = 208;
getNum = "137xxxx9706";
try {
imgBack = Image.createImage("/back.png");
imgButton1 = Image.createImage("/button1.png");
} catch (IOException e) {
e.printStackTrace();
}
currentState = 1;
thread = new Thread(this);
thread.start();
}


protected void paint(Graphics g) {
this.g = g;
if (currentState != 5)
g.drawImage(imgBack, canvasWidth / 2, canvasHeight / 2, 0x1 | 0x2);
switch (currentState) {
default:
break;

case 1: // '\001'
if (logoi != 0) {
g.drawImage(imgButton1, (canvasWidth - imgButton1.getWidth())
/ 2 + logoi, (canvasHeight * 5) / 6, 0);
logoi = 0;
} else {
g.drawImage(imgButton1,
(canvasWidth - imgButton1.getWidth()) / 2,
(canvasHeight * 5) / 6, 0);
logoi = 1;
}
break;

case 2: // '\002'
g.drawImage(imgMenuBack,
(canvasWidth - imgMenuBack.getWidth()) / 2,
canvasHeight / 9, 0);
if (logoi != 0) {
g.drawImage(imgButton1, (canvasWidth - imgButton1.getWidth())
/ 2 + logoi, (canvasHeight * 5) / 6, 0);
logoi = 0;
} else {
g.drawImage(imgButton1,
(canvasWidth - imgButton1.getWidth()) / 2,
(canvasHeight * 5) / 6, 0);
logoi = 1;
}
g.setClip(0, 0, canvasWidth, imgMenuBack.getHeight());
g.drawImage(imgIntro, 0, playCount, 0);
if (playCount > 25)
playCount -= 3;

break;

case 3: // '\003'
g.drawImage(imgMenuBack,
(canvasWidth - imgMenuBack.getWidth()) / 2,
canvasHeight / 9, 0);
g.drawImage(imgButton2, (canvasWidth - imgButton2.getWidth()) / 2,
(canvasHeight - imgButton2.getHeight()) / 2 + 5, 0);
g.drawImage(imgButton3, x, y, 0);
g.drawImage(imgSignName,
(canvasWidth - imgSignName.getWidth()) / 2,
(canvasHeight - imgSignName.getHeight()) / 2 + 8, 0);
g.drawImage(imgExit, 0, canvasHeight - imgExit.getHeight(), 0);
g.drawImage(imgChoose, canvasWidth - imgChoose.getWidth(),
canvasHeight - imgChoose.getHeight(), 0);
break;

case 4: // '\004'
g.drawImage(imgCharge, (canvasWidth - imgCharge.getWidth()) / 2,
canvasHeight / 9, 0);
g.drawImage(imgGoBack, 0, canvasHeight - imgGoBack.getHeight(), 0);
g.drawImage(imgSend, canvasWidth - imgSend.getWidth(),
canvasHeight - imgSend.getHeight(), 0);
break;
}
}

protected void keyPressed(int keyCode) {
switch (currentState) {
case 5: // '\005'
default:
break;

case 3: // '\003'
switch (keyCode) {
case -7:
case -5:
switch (recentChoose) {
case 0: // '\0'
updateState(this.stateSend, this.stateMenu);
break;
case 1:
updateState(this.stateSend, this.stateMenu);
break;
case 2:
updateState(this.stateSend, this.stateMenu);
break;
case 3:
updateState(this.stateSend, this.stateMenu);
break;
case 4:
updateState(this.stateSend, this.stateMenu);
break;
case 5:
updateState(this.stateSend, this.stateMenu);
break;
}
break;
case 4: // '\004'
switch (keyCode) {
case -6:

updateState(this.stateMenu, this.stateSend);
break;

case -7:
case -5:
currentState = 5;
sendCommand = new Command("发送", 4, 1);
backCommand = new Command("返回", 7, 1);

massage = new TextField(null, null, 256, 0);
alert2 = new StringItem(null, "输入您要发送的内容（中文）：", 0);
alert3 = new StringItem(null, "发送成功！", 0);
form = new Form("诗");
form.append(alert2);
form.append(massage);
form.addCommand(backCommand);
form.addCommand(sendCommand);
form.setCommandListener(this);
if(midlet.display==null)
midlet.display=Display.getDisplay(midlet);
Display.getDisplay(midlet).setCurrent(form);
break;
}
break;
}
}
public void run() {
do
try {
alertWin=new Alert(null,"短信发送成功，谢谢使用！",null,AlertType.WARNING);
if(midlet.display==null)
midlet.display=Display.getDisplay(midlet);

Display.getDisplay(midlet).setCurrent(alertWin);
isWin = false;
}
if (isNull) {

alertNull=new Alert(null,"对不起，短信不能为空！",null,AlertType.WARNING);
if(midlet.display==null)
midlet.display=Display.getDisplay(midlet);
Display.getDisplay(midlet).setCurrent(alertNull);
isNull = false;
}
Thread.sleep(100L);
repaint();
System.gc();
} catch (InterruptedException e) {
e.printStackTrace();
}
while (true);
}
public void commandAction(Command c, Displayable d) {
if (c == backCommand) {
if(midlet.display==null)
{
midlet.display=Display.getDisplay(midlet);
System.out.println("sdfsa");
}
Display.getDisplay(midlet).setCurrent(this);
updateState(this.stateMenu, this.stateSMS);

}
if (c == sendCommand)
{
getMassage = massage.getString();

if (getMassage.equals(""))// 如果用户输入的是空字符串
{
System.out.println("短信是空！");
this.updateState(this.stateNull, this.stateSend);
isNull = true;
}

else {

updateState(this.stateDo, this.stateSend);
(new Thread() {
public void run() {
isWin = SMSUtil.send(getMassage, getNum);
} }).start();
System.out.println(isWin);
}
}
if (c == backCommandNull) {
if(midlet.display==null)
midlet.display=Display.getDisplay(midlet);
// midlet.display.setCurrent(this);
Display.getDisplay(midlet).setCurrent(this);
updateState(this.stateSend, this.stateNull);
}
}

}