包中的类 - 线程“main”中的异常 java.lang.NoClassDefFoundError

Question

I am trying to run a jar file in Hadooop (Ubuntu Linux).

My file 'Project1.java' has a package defined, before the class, like this:

package myPackage.comp;
public class Project1 {
---lines of code here---
}

I use the following commands to try to run it:

$ hadoop com.sun.tools.javac.Main Project1.java
$ jar cf proj1.jar Project1*.class
$ hadoop jar proj1.jar Project1 input output

and I get the following error:

Exception in thread "main" java.lang.NoClassDefFoundError: comp/proj1/Project1 (wrong name: Project1)
    at java.base/java.lang.ClassLoader.defineClass1(Native Method)
    at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1017)
    at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:174)
    at java.base/java.net.URLClassLoader.defineClass(URLClassLoader.java:550)
    at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:458)
    at java.base/java.net.URLClassLoader$1.run(URLClassLoader.java:452)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:451)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:589)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
    at java.base/java.lang.Class.forName0(Native Method)
    at java.base/java.lang.Class.forName(Class.java:398)
    at org.apache.hadoop.util.RunJar.run(RunJar.java:316)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:236)

When I look into the generated proj1.jar file, I can see a Project1.java class file in it.

What am I missing here?

Update : If I remove the line

package myPackage.comp;

It works perfectly.

How can I get it to work when including the class in a package?

Answer 1

Every project must have a class called main. So if you write main instead of Project1, the problem is solved.