Question

我已经浏览过这个网站一段时间了，但这是我的第一篇官方帖子。

我是Java的新手（刚刚开始使用applet），而且我在分配的applet在浏览器中运行时遇到了麻烦。 Eclipse中的所有内容都运行正常，但是当我打开.html文件时，只有空格。

如果有人能够查看下面的内容并提供他们的专业知识，我将非常感激。我确定我已经犯了一些noob错误，并且还没能找到它。感谢。

Java源代码：

// Import necessary classes.
import java.applet.*;
import java.awt.*;
import java.awt.event.*;

class Eye extends Thread
{
    public static int mouseXcoordinate;
    public static int mouseYcoordinate;
    private static final int EYEWIDTH = 50;
    private static final int EYEHEIGHT = 75;
    private static final int IRISSIZE = 30;
    private static final int PUPILSIZE = 12;
    private Color irisColor;
    private static final int SMALLXRAD = (EYEWIDTH  - IRISSIZE)/2;
    private static final int SMALLYRAD = (EYEHEIGHT - IRISSIZE)/2;
    private int x, y;
    private double newX, newY;
    private Graphics g;

    // Constructor for a new eye.
    public Eye(int x, int y, Graphics g)
    {
        this.g = g;
        this.x = x;
        this.y = y;

        // Choose random colors for the iris of the eyes.
        irisColor = new Color((float)Math.random(), (float)Math.random(), (float)Math.random());
    }

    // Draw the eye, in detail.
    private void draw()
    {
        synchronized(g)
        {
            // Erase any old eye color.
            g.setColor(Color.white);
            g.fillOval(x - EYEWIDTH/2, y - EYEHEIGHT/2, EYEWIDTH, EYEHEIGHT);
            // Draw the iris and set the color.
            g.setColor(irisColor);
            g.fillOval((int)newX - IRISSIZE/2 + 1, (int)newY - IRISSIZE/2 + 1, IRISSIZE, IRISSIZE);
            // Draw the pupil and set the color.
            g.setColor(Color.black);
            g.fillOval((int)newX - PUPILSIZE/2 + 1, (int)newY - PUPILSIZE/2 + 1, PUPILSIZE, PUPILSIZE);
            // Draw the eye outline.
            g.drawOval(x - EYEWIDTH/2, y - EYEHEIGHT/2, EYEWIDTH, EYEHEIGHT);
        }
    }

    // Continuously calculate the current coordinates and redraw the eyes to follow the coordinates.
    public void run()
    {
        for(;;)
        {
            updateCoordinates();
            draw();
            try
            {
                sleep(50);
            }
            catch (InterruptedException e)
            {}
        }

    }

    // Update the mouse coordinates.
    private void updateCoordinates()
    {

        if (mouseXcoordinate == x)
        {
            newX = mouseXcoordinate;

            if (Math.abs(y - mouseYcoordinate) >= SMALLYRAD)
            {
                if ( (y - mouseYcoordinate) > 0 )
                    newY = y - SMALLYRAD;
                else
                    newY = y + SMALLYRAD;
            }
            else
                newY = mouseYcoordinate;
            return;
        }

        // Find intersection point of line to mouse with eye ellipse
        double slope = (double)(mouseYcoordinate - y) / (double)(mouseXcoordinate - x);
        double numerator = SMALLXRAD * SMALLXRAD * SMALLYRAD * SMALLYRAD;
        double denominator = SMALLYRAD * SMALLYRAD + slope * slope * SMALLXRAD * SMALLXRAD;
        newX = Math.sqrt(numerator / denominator);
        newY = slope * newX;

        // Choose appropriate intersection point
        if (mouseXcoordinate < x)
            newX = -Math.abs(newX);
        else
            newX = Math.abs(newX);

        if (mouseYcoordinate < y)
            newY = -Math.abs(newY);
        else
            newY = Math.abs(newY);

        newX += x;
        newY += y;

        if ( (double)(mouseXcoordinate - x)*(mouseXcoordinate - x) / (SMALLXRAD * SMALLXRAD) + (double)(mouseYcoordinate - y)*(mouseYcoordinate - y) / (SMALLYRAD * SMALLYRAD) < 1 )
        {
            newX = mouseXcoordinate;
            newY = mouseYcoordinate;
        }
    }
}

@SuppressWarnings("serial")
public class BurleighWatchMe extends Applet
{
    static final int NUM_EYES = 50;
    Eye[] eyes = new Eye[NUM_EYES];
    int count = -1;
    int width, height;

    // Initializes the applet by loading coordinates and starting two eye threads.
    public void init()
    {
        addMouseMotionListener( new MouseMotionListener()
        {
            public void mouseDragged(MouseEvent e) {}
            public void mouseMoved(MouseEvent e)
            {
                Eye.mouseXcoordinate = e.getX();
                Eye.mouseYcoordinate = e.getY();
                repaint();
            }
        });
    }

    // Starts the eye threads.
    public void start()
    {
        if (count == -1)
        {
            width = getSize().width;
            height = getSize().height;
            final Graphics g = getGraphics( );
            eyes[++count] = new Eye(width/4,   height/2, g);
            eyes[count].start();
            eyes[++count] = new Eye(3*width/4, height/2, g);
            eyes[count].start();
        }

    repaint();
    }

    // Redraws a border around the applet.
    public void update(Graphics g)
    {
        g.drawRect(0,0,width-1,height-1);
    }
}

HTML：

<html>
<head>
    <title>Watch Me Eyes</title>
</head>
<body>
    Move your mouse pointer over these<br />eyes, and watch them follow it!
    <p />
    <applet code="BurleighWatchMe.class" width="400" height="400">
    </applet>
</body>
</html>

Answer 1

在HTML代码中，您错过了添加codebase标记的applet属性。代码库是指包含applet的目录。所以如果APPLET与HTML PAGE不在同一目录，那么您必须在codebase标记内添加applet属性。它将采用以下形式：

<applet>
    codebase="E:\Projects\" code="BurleighWatchMe.class" height="400" width="400"
</applet>

假设 E：\ Projects 目录中存在 BurleighWatchMe.class 。

但是，如果 BurleighWatchMe.class 文件与 HTML 页面位于同一目录中，并且您仍然看到一个空白页面，那么它可能会是因为您系统上的 JRE 不允许使用未知的applet。您需要做的是编辑设置以允许本地小程序。为此，请转到Start > Configure Java。转到Java设置对话框的Security选项卡。在窗口的下半部分，您可以看到网站例外列表。除此之外，还有一个名为编辑网站列表... 的按钮。单击该按钮。您将看到可以运行其小程序的站点列表。点击添加以添加新位置。在新字段中，键入file:///并按Enter键。它会向你显示警告;点击继续。现在单击OK并退出Configure Java程序。

接下来，重新启动浏览器。加载小程序时，您会看到一个对话框，您必须选择运行选项。您现在应该可以在浏览器上运行applet了。

请注意谷歌浏览器不再支持小程序。我所知道的支持applet的唯一浏览器是 Firefox 和 Internet Explorer 。我测试了它，它适用于这两个浏览器。

看看它是否解决了你的问题。

为什么applet不是在浏览器中运行而是在IDE中运行？

1 个答案: