我正在尝试为我的网络课程运行这些applet。当我尝试通过链接在浏览器中运行它们时，它们什么也没做。因此，我决定尝试在IntelliJ中编译它们，但是当我运行代码时，它什么也没做。没有返回错误信息。我从源代码更改代码的唯一做法是添加main方法并删除包声明。以下是我尝试运行的小程序：

JAVA代码

///////////////////////////////////////
//LineSimApllet
//written by David Grangier, Institut Eurecom, France
//[email protected]
///////////////////////////////////////
//imports

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.applet.*;
import java.util.*;

//Applet Class
public class LineSimApplet extends Applet {
    //buttons
    Button start = new Button("Start");
    Button stop = new Button("Reset");
    //features lists
    MyChoice length = new MyChoice(new String[]{"10 km", "100 km", "1000 km"}, new double[]{10E3, 100E3, 1E6}, 3);
    MyChoice rate = new MyChoice(new String[]{"512 kps", "1 Mbps", "10 Mbps", "100 Mbps"}, new double[]{512E3, 1E6, 10E6, 100E6}, 2);
    MyChoice size = new MyChoice(new String[]{"100 Bytes", "500 Bytes", "1 kBytes"}, new double[]{8E2, 4E3, 8E3}, 1);
    //to simulate time
    Thread timerThread;
    TickTask timerTask;
    boolean simulationRunning = false;
    //communication line
    Line myLine;

    public void init() {
        try {
            setBackground(Color.white);
            add(new Label("Length", Label.RIGHT));
            add(length);
            add(new Label("Rate", Label.RIGHT));
            add(rate);
            add(new Label("Packet size", Label.RIGHT));
            add(size);
            //start
            start.addActionListener(
                    new ActionListener() {
                        public void actionPerformed(ActionEvent event) {
                            launchSim();
                        }
                    });
            add(start);
            //stop
            Button stop = new Button("Reset");
            stop.addActionListener(
                    new ActionListener() {
                        public void actionPerformed(ActionEvent event) {
                            stopSim();
                            //clear line
                            myLine.sendTime(0);
                            //redraw cleared line
                            LineSimApplet.this.repaint();
                        }
                    });
            add(stop);
            //line
            myLine = new Line(40, 50, 450, 10);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void paint(Graphics g) {
        update(g); // eliminate flashing : update is overriden
    }

    public void update(Graphics g) { //work on a offscreen image

        Dimension offDimension = getSize();
        Image offImage = createImage(offDimension.width, offDimension.height);
        Graphics offGraphics = offImage.getGraphics();
        myLine.drawLine(offGraphics);

        //sender
        offGraphics.setColor(Color.blue);
        offGraphics.fillRect(10, 40, 30, 30);
        offGraphics.setColor(Color.black);
        offGraphics.drawString("Sender", 5, 90);
        offGraphics.drawRect(10, 40, 30, 30);

        //receiver
        offGraphics.setColor(Color.blue);
        offGraphics.fillRect(490, 40, 30, 30);
        offGraphics.setColor(Color.black);
        offGraphics.drawString("Receiver", 485, 90);
        offGraphics.drawRect(490, 40, 30, 30);

        offGraphics.drawString("Propagation speed : 2.8 x 10^8 m/sec", 175, 105);
        //display offscreen image
        g.drawImage(offImage, 0, 0, this);
    }

    private void launchSim() {
        setupEnabled(false);
        //setup line
        myLine.setup(length.getVal(), rate.getVal());
        myLine.emitPacket(size.getVal(), 0);
        //setup timer
        timerTask = new TickTask(1E-5, myLine.totalTime());
        timerThread = new Thread(timerTask);
        //start simulation
        simulationRunning = true;
        timerThread.start();
    }

    private void stopSim() {
        timerTask.endNow();
        simulationRunning = false;
        setupEnabled(true);
    }

    public void setupEnabled(boolean value) {
        start.setEnabled(value);
        length.setEnabled(value);
        rate.setEnabled(value);
        size.setEnabled(value);
    }

    //my choice
    class MyChoice extends Choice {
        private double vals[];

        public MyChoice(String items[], double values[], int defaultValue) {
            for (int i = 0; i < items.length; i++) {
                super.addItem(items[i]);
            }
            vals = values;
            select(defaultValue - 1);
        }

        public double getVal() {
            return vals[super.getSelectedIndex()];
        }
    }

    //tickTask
    class TickTask implements Runnable {
        private double counter;
        private double length;
        private double tick;

        public TickTask(double t, double l) {
            length = l;
            tick = t;
            counter = 0;
        }

        public void run() {
            while (LineSimApplet.this.simulationRunning) {
                counter += tick;
                LineSimApplet.this.myLine.sendTime(counter);
                LineSimApplet.this.repaint();
                if (counter >= length) {
                    LineSimApplet.this.myLine.clearPackets();
                    LineSimApplet.this.timerThread.suspend();
                }
                try {
                    LineSimApplet.this.timerThread.sleep(50);
                } catch (Exception e) {
                }
            }
        }

        public void endNow() {
            length = counter;
        }
    }
}

//Line class
class Line {
    //graphic variables
    private int gX;
    private int gY;
    private int gWidth;
    private int gHeight;
    //characteristic variables
    final double celerity = 2.8E+8;
    private double length;
    private double rate;
    //simulation variables
    private double time;
    private Packet myPacket;

    public Line(int x, int y, int w, int h) {
        //graphic init
        gX = x;
        gY = y;
        gWidth = w;
        gHeight = h;
    }

    public void setup(double l, double r) {
        length = l;
        rate = r;
    }

    void sendTime(double now) {
        time = now; //update time
        removeReceivedPackets(now);
    }

    void emitPacket(double s, double eT) {
        myPacket = new Packet(s, eT);
    }

    private void removeReceivedPackets(double now) {
        if (!(myPacket == null)) {
            if (now > myPacket.emissionTime + (myPacket.size / rate) + length * celerity) {
                clearPackets();
            }
        }
    }

    public void clearPackets() {
        myPacket = null;
    }

    public double totalTime() {
        double emmissionTime = (myPacket.size / rate);
        double onLineTime = (length / celerity);
        return (emmissionTime + onLineTime);
    }

    public void drawLine(Graphics g) {
        g.setColor(Color.white);
        g.fillRect(gX, gY + 1, gWidth, gHeight - 2);
        g.setColor(Color.black);
        g.drawRect(gX, gY, gWidth, gHeight);
        g.setColor(Color.red);
        g.drawString(timeToString(time), gX + gWidth / 2 - 10, gY + gHeight + 15);
        drawPackets(g);
    }

    private void drawPackets(Graphics g) {
        if (!(myPacket == null)) {
            double xfirst;
            double xlast;
            //compute time units
            xfirst = time - myPacket.emissionTime;
            xlast = xfirst - (myPacket.size / rate);
            //compute position
            xfirst = xfirst * celerity * gWidth / length;
            xlast = xlast * celerity * gWidth / length;
            if (xlast < 0) {
                xlast = 0;
            }
            if (xfirst > gWidth) {
                xfirst = gWidth;
            }
            //draw
            g.setColor(Color.red);
            g.fillRect(gX + (int) (xlast), gY + 1, (int) (xfirst - xlast), gHeight - 2);
        }
    }

    static private String timeToString(double now) {
        String res = Double.toString(now * 1000);
        int dot = res.indexOf('.');
        String deci = res.substring(dot + 1) + "000";
        deci = deci.substring(0, 3);
        String inte = res.substring(0, dot);
        return inte + "." + deci + " ms";
    }

    public static void main(String[] args) {
        LineSimApplet ls = new LineSimApplet();
        ls.init();
    }
}

class Packet {
    double size;
    double emissionTime;

    Packet(double s, double eT) {
        size = s;
        emissionTime = eT;
    }
}

如何使用IntelliJ运行此applet？