帮忙看看CommmandListener哪里错了

[chaoliu1024]

import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;  // 提示没有导入
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.Ticker;

public class CommandTicker extends MIDlet {

    private Display display;
    private Form f;

    public CommandTicker() {
        super();
    }

    protected void startApp() throws MIDletStateChangeException {
        display = Display.getDisplay(this);
        f = new Form("Ticker测试");
        Command start = new Command("开始", Command.OK, 1);
        Command stop = new Command("退出", Command.STOP, 1);
        f.addCommand(start);
        f.addCommand(stop);
        f.setCommandListener(this);  // 这里报错,好像this有问题
        display.setCurrent(f);
    }

    protected void pauseApp() {
    }

    protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
    }

    public void commandAction(Command c, Displayable s) {
        String cmd = c.getLabel();
        if (cmd.equals("开始")) {
            f.setTicker(new Ticker("运行中..."));
        } else if (cmd.equals("退出")) {
            f.setTicker(new Ticker(null));
        }
    }
}

[ifengshow]

帮看看了，但我看不出问题来

[xiang1115]

public class CommandTicker extends MIDlet {

改为
public class CommandTicker extends MIDlet implements CommandListener{

[kircheis_tree]

改成：
public class CommandTicker extends MIDlet implements CommandListener

你没有实现CommandListener吗。。。

[xiaxia421]

你没有实现CommandListener接口

[chaoliu1024]

我知道哪里错了...