Question

I have a simple Class

package chapter10;

public class CompilationTest {


  public static void main(String[] args) {
    System.out.println("HELLO WORLD");
  }

}

The path is

Test\src\chapter10\CompilationTest.java

I successfully compiled the code into the same folder and now I have

Test\src\chapter10\CompilationTest.class

However when I try to run from the same folder it I get this error

>java CompilationTest


Exception in thread "main" java.lang.NoClassDefFoundError: CompilationTest (wrong name: chapter10/CompilationTest)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(Unknown Source)
        at java.lang.ClassLoader.defineClass(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$000(Unknown Source)
        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: CompilationTest.  Program will exit.

When I run using

>java chapter10/PropertiesTest

Exception in thread "main" java.lang.NoClassDefFoundError: chapter10/PropertiesTest
Caused by: java.lang.ClassNotFoundException: chapter10.PropertiesTest
        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: chapter10/PropertiesTest.  Program will exit.

Answer 1

The class is in the chapter10 package. Run it from the parent directory as:

java chapter10.CompilationTest

The reason for going to the parent is that Java is searching its CLASSPATH, which includes the current directory, for a chapter10 directory containing a CompilationTest.class file. You could also add the src directory’s absolute path to the CLASSPATH to achieve the same effect:

set CLASSPATH=C:\...\Test\src
java chapter10.CompilationTest

Or (apparently this is better style) add the -cp or -classpath argument to java:

java -cp "C:\...\Test\src" chapter10.CompilationTest