NoClassDefFoundError when compiling a HelloWorld programming to a jar

Question

Here's what I've got.

I've got my 'MyJava' folder which everything is contained in.

MyJava/src/a/HelloWorld.java
MyJava/src/b/Inner.java
MyJava/bin/
MyJava/manifest.txt

HelloWorld.java:

public class HelloWorld {

    public static void main(String[] args) {

        System.out.println("Hello, World");

        Inner myInner = new Inner(); 
        myInner.myInner(); 
    }
}

Inner.java:

public class Inner {

    public void myInner() {
        System.out.println("Inner Method");
    }
}

Manifest.txt:

Main-Class: HelloWorld

First I compile the .javas to .class:

javac -d bin src/a/HelloWorld.java src/b/Inner.java

Now I put these into a .jar file jar cvfm myTwo.jar manifest.txt bin/*.class

now I try run the jar: java -jar myTwo.jar

And I get:

Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld
...
Could not find the main class: HelloWorld. Program will exit.

I know this is a pretty simple problem, what am I missing?

Well... I'm playing around with working out how I'd compile for something. Though the something similar does use packages. — dwjohnston, May 15 '13 at 07:38
Packages in Java source on the local file system usually correspond to the directory in which the source is kept. So if a class had package `pkg.name` & name `MyClass` it should be in path a `pkg/name/MyClass.java`. I recommend if your classes are both in the same package (the default package it seems) they should be in the same directory. There are ways to do it differently, but I suggest you stick with the simplest way for the moment. — Andrew Thompson, May 15 '13 at 08:03

score 2 · Accepted Answer · answered May 15 '13 at 08:16

If you examine the files inside your .JAR you will notice that your compiled classes are inside the bin directory (and therefore cannot be found, since your manifest references a class in the top level).
Change your jar... command like this:

jar cvfm myTwo.jar manifest.txt -C bin .

See also the "Creating a JAR File" section of the Java Tutorial.

score 0 · Answer 2 · answered May 15 '13 at 09:53

0

One of the solutions is to add the following line to the manifest.txt

Class-Path: bin/

Then you can use 'your' command for the jar creation:

jar cvfm myTwo.jar manifest.txt bin/*.class

answered May 15 '13 at 09:53

Łukasz Rzeszotarski

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NoClassDefFoundError when compiling a HelloWorld programming to a jar

2 Answers2