线程“ main”中的异常java.lang.NoClassDefFoundError：org / javatuples / Unit

Question

I have imported the javatuples-1.2.jar in Eclipse project. I did this to run the Java Tuples Unit class program. The following is the code:

 package mynewpackage;
 import org.javatuples.Unit; 

 class Mynewclass2 { 
  public static void main(String[] args) 
   { 
    Unit<String> u 
        = new Unit<String>("This is demo text!"); 

    System.out.println(u); 
   } 
 } 

But, getting the following error on running:

Exception in thread "main" java.lang.NoClassDefFoundError: org/javatuples/Unit
    at mynewpackage.Mynewclass2.main(Mynewclass2.java:9)
Caused by: java.lang.ClassNotFoundException: org.javatuples.Unit
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
    ... 1 more

Under the references, I can easily see that the tuples jar file is successfully added. However, the following is the project directory, jar in references, error, and the entire program in Eclipse.

How can I fix the issue and run Java Tuples programs correctly?

Answer 1

Right Click on javatuples-1.2.jar > Build path > Add to Build Path .

NoClassDefFoundError is an error that is thrown when the Java Runtime System tries to load the definition of a class, and that class definition is no longer available.

Comments are Welcome.

Answer 2

You have java 11 in place...

When I (try to) reproduce your setup:

1. My eclipse (Version: 2018-12 (4.10.0), Win_64_jdk_11.0.2) asks me for "module name" and adds src/module-info.java after creation of a "Java Project", ... then download and add lib/javatuples-1.2.jar to build path.

2. When I try to use/import it in my code (main class) - compilation error, and auto-correct proposes me to add "javatuples" module to module-info:

click-clack:

myproject/src/module-info.java

module myproject {
   requires javatuples;
}

After that the program is already runnable, but Eclipse warns :

Name of automatic module 'javatuples' is unstable, it is derived from the module's file name.

To fix this, you can run (from command line):

myproject>jar --file=lib/javatuples-1.2.jar --describe-module
No module descriptor found. Derived automatic module.

javatuples@1.2 automatic
requires java.base mandated
contains org.javatuples
contains org.javatuples.valueintf

So, eclipse warning is already sort of nasty: javatuples is the "correct" module name.

Hope it helps.