Java Applet work only on my computer?

问题

I'm developing a Java applet that show a message box when you visit the site. This is my Java code:

import java.applet.Applet;
import javax.swing.JOptionPane;
public class JavaRun extends Applet {
    private static final long serialVersionUID = 1L; 
    public void init()
    { 
        JOptionPane.showMessageDialog(null, "hello world!");     
    }
}

This is the html:

<applet width='100' height='100' code='JavaRun' archive='data.jar'>
</applet>

On my computer (that have the java SDK) it's work, but when I'm using it on my laptop that have only the standard Java, I get these errors:

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.UnsupportedClassVersionError: Micro : Unsupported major.minor version 51.0...
enter code here

回答1:

I believe You have different versions of Java environments on your computers. Run this command on both computers

java -version

And compare version numbers. Probably should run

javac -version

on Your development machine. If you get different version numbers update Java runtime environment on your laptop.

回答2:

UnsupportedClassVersionError: Micro : Unsupported major.minor version 51.0

This is the problem. You've compiled your applet with a class version that is not supported by the JVM you're running on the other system.

Use the -target flags for javac to produce class files for a given target JVM version.

回答3:

UnsupportedClassVersionError

• To compile code for a particular Java version, use the cross-compilation options. To do this properly will require an rt.jar of the target version (to use the bootclasspath option of javac).
• To deploy code that requires a particular version, use deployJava.js
• To maintain your sanity and provide a better user experience, convert the applet to an application and launch it from a link using Java Web Start.

来源：https://stackoverflow.com/questions/9546359/java-applet-work-only-on-my-computer