import javax.microedition.lcdui.*;

public class ThreadWait implements Runnable {
    private int sec;

    private Form form;

    private String msg;

    public ThreadWait(int sec, Form form, String msg) {
        this.sec = sec;
        this.form = form;
        this.msg = msg;
        new Thread(this).start();
    }

    public void run() {
        try {
            if (form != null) {
                Gauge gauge = new Gauge(msg, false, 100, Gauge.CONTINUOUS_IDLE);
                form.append(msg);
                int k = form.append(gauge);
                while (gauge.getValue() != gauge.getMaxValue()) {
                    gauge.setValue(gauge.getValue() + 1);
                    Thread.sleep(10 * sec);
                }
                form.delete(k);

            }
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

------解决方案--------------------
package prj10_2;

import javax.microedition.lcdui.*

public class frm_MIDLet1 extends Form implements CommandListener,
		ItemStateListener, ItemCommandListener {
	private static frm_MIDLet1 frm;
	private TextField tf_id = new TextField("用户名", "", 20, TextField.ANY);
	private TextField tf_pw = new TextField("密  码", "", 20, TextField.NUMERIC
			| TextField.PASSWORD);
	private Command Cmd_login = new Command("登陆", Command.SCREEN, 1);
	private Command Cmd_del = new Command("删除", Command.BACK, 1);

	public frm_MIDLet1() {
		super("登陆界面");
		frm = this;
		this.append(tf_id);
		this.append(tf_pw);
		this.addCommand(Cmd_login);
		this.setCommandListener(this);
		this.setItemStateListener(this);
	}

	public void commandAction(Command c, Displayable d) {
		if (c == Cmd_login) {
				Gauge g = new Gauge("登陆验证", false, 100, 0);
				frm.append(g);
				thread_gauge tg = new thread_gauge(g);
				tg.start();
				try {
					tg.join();
				} catch (Exception ex) {
					ex.printStackTrace();
				}
				System.out.println("验证完毕");
		}
	}

	public void commandAction(Command c, Item i) {
		TextField tf = (TextField) i;
		int p = tf.getCaretPosition();