JApplet中的InvocationTargetException

Question

当我在JFrame中正常运行此文件时，它可以正常运行：

package Gadgets;

import java.awt.Button;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Label;
import java.awt.event.ActionEvent;
import java.text.*;
import javax.swing.*;
public class timer extends JApplet {
    private int time = 0;
    public timer() {
        NumberFormat twoNumbers = new DecimalFormat("00");
        Box timerBox = new Box(BoxLayout.Y_AXIS);
        Label time = new Label("00:00:00");
        Container options = new Container();
        options.setLayout(new BoxLayout(options, BoxLayout.X_AXIS));
        Box startBox = new Box(BoxLayout.X_AXIS);
        Button start = new Button("Start");
        Box stopBox = new Box(BoxLayout.X_AXIS);
        Button stop = new Button("Stop");
        Box resetBox = new Box(BoxLayout.X_AXIS);
        Button reset = new Button("Reset");
        timerBox.add(time);
        timerBox.setPreferredSize(new Dimension(60, 20));

        Timer timer = new Timer(1000, (ActionEvent e) -> {
            time.setText(twoNumbers.format(Math.floor(this.time / (60*60))) + ":" + twoNumbers.format(Math.floor(this.time / 60)) + ":" + twoNumbers.format(this.time++ % 60));
        });
        start.addActionListener((ActionEvent e) -> {
            timer.start();
        });
        stop.addActionListener((ActionEvent e) -> {
            timer.stop();
        });
        reset.addActionListener((ActionEvent e) -> {
            timer.stop();
            this.time = 0;
            time.setText("00:00:00");
        });
        startBox.add(start);
        stopBox.add(stop);
        resetBox.add(reset);
        options.add(startBox);
        options.add(stopBox);
        options.add(resetBox);
        add(timerBox);
        add(options);
    }
    public static void main(String[] args) {

    }
}

但是，当我在JApplet中运行它时，它会显示InvocationTargetException。当我点击“更多细节”时，它不会解开异常。可能的原因是什么？
提前谢谢。