Java applet Error … What is wrong?

问题

Java applet code

package M257Applet

import java.applet.*;

import javax.swing.*;

import java.awt.*;

public class HellowApplet extends JApplet {

    public  void init(){

        Container cp = getContentPane();
        JLabel lb = new JLabel("Hellowwwww");
        cp.add(lb);
    }

}

html file

<html>
<head>
<title>Applet</title>
</head>
<body>
<APPLET CODE = HellowApplet.class  WIDTH =  400   HEIGHT = 400 >
</APPLET>
</body>
</html>

Error

Java Plug-in 1.6.0_22
Using JRE version 1.6.0_22-b04 Java HotSpot(TM) Client VM
User home directory = C:\Users\pc
----------------------------------------------------
c:   clear console window
f:   finalize objects on finalization queue
g:   garbage collect
h:   display this help message
l:   dump classloader list
m:   print memory usage
o:   trigger logging
q:   hide console
r:   reload policy configuration
s:   dump system and deployment properties
t:   dump thread list
v:   dump thread stack
x:   clear classloader cache
0-5: set trace level to <n>
----------------------------------------------------


java.lang.NoClassDefFoundError: HellowApplet (wrong name: M257Applet/HellowApplet)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(Unknown Source)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Exception: java.lang.NoClassDefFoundError: HellowApplet (wrong name: M257Applet/HellowApplet)

回答1:

Problem is with the package. You need to change the code attribute of applet, and based on where you have placed your HTML, the codebase attribute too. You have to place HellowApplet.class in a directory called M257Applet (because that is the package you have given), and the applet tag should look something like:

<applet code="M257Applet.HellowApplet" ... ></applet>

For this to work, your HTML has to be in the same directory as M257Applet (not inside M257Applet). Alternatively, you can specify the codebase attribute. For eg, with the following directory structure:

somedir
  +-- hello.html
  +-- M257Applet
  |    +-- HellowApplet.class

the applet will work. If however, you had

anotherdir
  +-- hello.html
  +-- somedir
  |   +-- M257Applet
  |   |    +-- HellowApplet.class

then you will have to specify codebase attribute like so:

<applet code="M257Applet.HellowApplet" codebase="somedir" ... ></applet>

So, you should have codebase pointing to the directory containing your package, and code has to have your package name also in it.

Edit: Please note, even though code="HellowApplet.class" will work, the correct way of specifying the applet is without the ".class" at the end.

回答2:

Your class is in a package. It's file name should match.

code="M257Applet/HellowApplet.class"

(It's a good idea to follow conventions. Package names should be all lower case.)

来源：https://stackoverflow.com/questions/6009767/java-applet-error-what-is-wrong

标签

java

html

swing

japplet