java - 开始 :applet not initialized when trying to open a frame in an applet

Question

我在 Herbert Schildt 的《java 2》一书中遇到了一段代码。这是代码。

import java.applet.Applet;

导入 java.awt.;导入 java.awt.event.;

public class SampleFrame extends Frame
{
    public SampleFrame(String title)
    {
        super(title);
        MyWindowAdapter wAdapter = new MyWindowAdapter(this);
        addWindowListener(wAdapter);
    }
    public void paint(Graphics g)
    {
        g.drawString("this is in the frame window", 10, 40);
    }

}
class MyWindowAdapter extends WindowAdapter
{
    SampleFrame sampleFrame;
    public MyWindowAdapter(SampleFrame sampleFrame)
    {
        this.sampleFrame = sampleFrame;
    }
    public void WindowClosing(WindowEvent we)
    {
        sampleFrame.setVisible(false);
    }
}
class MyApplet extends Applet
{
    Frame f;
    public void init()
    {
        f = new SampleFrame("a frame window");
        f.setSize(250, 250);
        f.setVisible(true);
    }
    public void start()
    {
        f.setVisible(true);
    }
    public void stop()
    {
        f.setVisible(false);
    }
    public void paint(Graphics g)
    {
        g.drawString("this is an applet window", 10, 20);
    }
}

根据这本书，它应该启动一个小程序，该小程序应该启动一个框架。但是当小程序在状态栏中启动时，它会显示“启动:小程序未初始化”为什么会这样？

我确实创建了小程序，但没有像这样将我的派生小程序类声明为公共(public)

import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;


class MouseEvents extends Applet implements MouseListener,
        MouseMotionListener
{
    String msg = "";
    int mouseX = 0 ,mouseY = 0 ,count=0;
    Boolean tPU ;
    private Point myPoint;

    public MouseEvents()
    {
        myPoint = new 
                Point();

    }

    public void init()
    {
        addMouseListener(this);
        addMouseMotionListener(this);
    }
    @Override
    public void mouseDragged(MouseEvent arg0)
    {
        // TODO Auto-generated method stub
        mouseX = arg0.getX();
        mouseY = arg0.getY();
        msg = "*";
        myPoint = arg0.getPoint();
        tPU = arg0.isPopupTrigger();
        count = arg0.getClickCount();
        arg0.translatePoint(100, 100);
        myPoint = arg0.getPoint();

        showStatus("dragging mouse at " + arg0.getX() + ", " +arg0.getY());
        showStatus("popUps ?"+tPU);
        showStatus("dragging mouse at " + myPoint.x + ", " +myPoint.y);
        showStatus("dragging mouse at " + myPoint.x + ", " +myPoint.y);
        showStatus("dragging mouse at " + myPoint.x + ", " +myPoint.y);

        repaint();
    }

    @Override
    public void mouseMoved(MouseEvent arg0)
    {
        // TODO Auto-generated method stub
        showStatus("moving mouse at " + arg0.getX() + ", " +arg0.getY());
    }

    @Override
    public void mouseClicked(MouseEvent e)
    {
        // TODO Auto-generated method stub
        mouseX=0;
        mouseY=10;
        msg="mouse clicked";
        repaint();
    }

    @Override
    public void mouseEntered(MouseEvent e)
    {
        // TODO Auto-generated method stub
        mouseX=0;
        mouseY=10;
        msg="mouse entered";
        repaint();
    }

    @Override
    public void mouseExited(MouseEvent e)
    {
        // TODO Auto-generated method stub
        mouseX=0;
        mouseY=20;
        msg="mouse exited";
        repaint();
    }

    @Override
    public void mousePressed(MouseEvent e)
    {
        // TODO Auto-generated method stub
        mouseX = e.getX();
        mouseY = e.getY();
        msg = "mouse pressed down";
        repaint();
    }

    @Override
    public void mouseReleased(MouseEvent e)
    {
        // TODO Auto-generated method stub
        mouseX = e.getX();
        mouseY = e.getY();
        msg = "mouse released up";
        repaint();
    }
    public void paint(Graphics g)
    {
        g.drawString(msg, mouseX, mouseY);
    }

}

Answer 1

如果您查看小程序控制台，您应该会看到错误的其余部分

MyApplet.class is not public or has no public constructor.

即将类声明为 public

public class MyApplet extends Applet {