相关疑难解决方法(0)

我在以下文件夹中安装了Java 1.7.0 C:\Program Files\Java.我的操作系统是带有Service Pack 3的Windows XP(版本2002).

我设置的环境变量是:

• CLASSPATH:C:\Program Files\Java\jdk1.7.0\jre\lib\rt.jar;

• 路径: C:\Program Files\Java\jdk1.7.0\bin;

• JAVA_HOME:C:\Program Files\Java;

我在这里介绍了我系统中的类名.

接下来我写了一个程序HelloWorld.java:

import java.io.*;

class HelloWorld
{
    public static void main(String[] args) 
    {
        System.out.println("Hello World!");
    }
}

当我编译使用javac HelloWorld.java它时,编译正常.

但在我发出后,我java HelloWorld遇到了以下错误:

Error: Could not find main class HelloWorld
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld
        at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:198)

Caused by: java.lang.ClassNotFoundException: HelloWorld
        at java.net.URLClassLoader$1.run(URLClassLoader.java:299)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:288)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:287)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:422)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:325)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:355)
        at …

我编写了以下Java源文件(Hello.java):

package com;

public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello!");
    }
}

我把它保存到C:/tmpjava/Hello.java.

从命令行,我导航到该目录并运行javac Hello.java.然后我跑dir:

• Hello.class
• Hello.java

然后,从我刚刚运行的同一目录javac,我运行java Hello.class并得到:

Exception in thread "main" java.lang.NoClassDefFoundError: Hello/class
Caused by: java.lang.ClassNotFoundException: Hello.class
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: Hello.class.  Program will exit.

这里发生了什么？!？怎么可以javac运行良好,但不是java吗？