Question

I created a List.java file in folder UtilityPack which contains this code

package Utilities;
public class List
{
    private class node{}
    public void insert(int data){}
    public void print(){}
    public static void main(String[] s){}
}

To compile i did

C:\UtilityPack>javac List.java

But when I try to run with

C:\UtilityPack>java -classpath . List

OR

C:\UtilityPack>java List

I get error

Exception in thread "main" java.lang.NoClassDefFoundError: List (wrong name: Uti
lities/List)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:14
2)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
        at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)

I have been trying to execute this program from last 3 hours but nothing worked..please help

Answer 1

You need the fully qualified name e.g.

java -cp . Utilities.List

i.e. you’re telling the JVM to look from the current direct (-cp .) for a class Utilities.List, which it will expect in the file Utilities\List.class.

To be more consistent you should put the .java file under a Utilities directory (yes – this is tautologous – the package specifies this, but it’s consistent practise).

I would also avoid calling your class List. At some stage you’re going to import a java.util.List and it’ll all get very confusing!

Finally, as soon as you get more than a couple of classes, investigate ant or another build tool, and separate your source and target directories.