java能编译，但运行时出现了下面的错误：求高手解决下，，，，
java能编译，但运行时出现了下面的错误：求高手解决下，，，，D:\java>java helloworld
Exception in thread "main" java.lang.NoClassDefFoundError: helloworld
Caused by: java.lang.ClassNotFoundException: helloworld
at (Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at (Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
D:\java>
