J2ME无线电应用程序错误。空指针异常

Question

我正在用java编写移动设备应用程序。我现在正试图检测手机中的无线电范围。在Sun Java WirelessToolkit模拟器中它可以工作，但在我的诺基亚301上它显示错误java.lang.NullPointerException。我不知道问题出在哪里。代码：

package mobileapplication5;
import javax.microedition.media.*;
import javax.microedition.media.Control.*;
import javax.microedition.amms.control.tuner.*;
import java.util.Date;
import javax.microedition.lcdui.Alert;
import javax.microedition.lcdui.AlertType;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Form;
import javax.microedition.midlet.*;

public class Midlet extends MIDlet {
    public Player radioPlayer;
    public TunerControl tunerControl;

    public Form form;

    public void startApp() {
        Display display = Display.getDisplay(this);

        form = new Form("Radio Test");
        display.setCurrent(form);
        try {
            radioPlayer = Manager.createPlayer("capture://radio");
            radioPlayer.realize();
            tunerControl = (TunerControl)
            radioPlayer.getControl("javax.microedition.amms.control.tuner.TunerControl");
            tunerControl.setStereoMode(TunerControl.STEREO);

            radioPlayer.start();

            int maxFM = tunerControl.getMaxFreq("fm");
            int minFM = tunerControl.getMinFreq("fm");
            String tx = Integer.toString(maxFM);
            tx = tx + " - " + Integer.toString(minFM);
  form.append("SET FM: "+tx);

        } catch (Exception ioe) {
            form.append("initializeRadio ioe "+ioe);
        }

    }

    public void pauseApp() {
    }

    public void destroyApp(boolean unconditional) {
    }
}

感谢。