编译正确，执行报错

[zytang]

E:\HelloWorld>java HelloWorld
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld (wrong nam
e: HelloWorld/HelloWorld)
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:486)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:11
1)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:248)
at java.net.URLClassLoader.access$100(URLClassLoader.java:56)
at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:297)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:286)
at java.lang.ClassLoader.loadClass(ClassLoader.java:253)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:313)

[bsd]

是不是在你的HelloWorld里有个
package HelloWorld;
那么你应该在命令行输入
E:\HelloWorld>java HelloWorld.HelloWorld

[thaliadbw]

set classpath=.