compilation - How do I run Java .class files?

Question

I've compiled a HelloWorld program, and I'm using the command prompt to run it. The .class file is named HelloWorld2.class

The file is located in C:UsersMattworkspaceHelloWorld2in Here's what I'm getting when I go to command prompt, and type "Java HelloWorld2" :

C:UsersMatt>Java HelloWorld2
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld2
Caused by: java.lang.ClassNotFoundException: HelloWorld2
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
Could not find the main class: HelloWorld2.  Program will exit.

I was expecting to see a HelloWorld printed out. What am I doing wrong? I have the JDK installed.

Answer 1

You need to set the classpath to find your compiled class:

java -cp C:UsersMattworkspaceHelloWorld2in HelloWorld2