Exception in Thread "Main" Java.Lang.Noclassdeffounderror: Helloworld

Exception in thread main java.lang.NoClassDefFoundError: HelloWorld

package main;

This means that your class resides in the main package, and its canonical name is main.HelloWorld.

Java requires that package names should also be mirrored in the directory structure. This means that:

1. Your HelloWorld.java file should be in a directory named main
2. You should execute javac and java from the directory containing main, not from main itself
3. The classpath should contain the directory where the main directory is, not main itself
4. java expects the canonical name of the class to execute, so main.HelloWorld

So, to recap:

You should have something like myproject/main/HelloWorld.java

From myproject, run javac main/HelloWorld.java

From myproject, run java -cp ./ main.HelloWorld

How can I solve java.lang.NoClassDefFoundError ?

After you compile your code, you end up with .class files for each class in your program. These binary files are the bytecode that Java interprets to execute your program. The NoClassDefFoundError indicates that the classloader (in this case java.net.URLClassLoader), which is responsible for dynamically loading classes, cannot find the .class file for the class that you're trying to use.

Your code wouldn't compile if the required classes weren't present (unless classes are loaded with reflection), so usually this exception means that your classpath doesn't include the required classes. Remember that the classloader (specifically java.net.URLClassLoader) will look for classes in package a.b.c in folder a/b/c/ in each entry in your classpath. NoClassDefFoundError can also indicate that you're missing a transitive dependency of a .jar file that you've compiled against and you're trying to use.

For example, if you had a class com.example.Foo, after compiling you would have a class file Foo.class. Say for example your working directory is .../project/. That class file must be placed in .../project/com/example, and you would set your classpath to .../project/.

Side note: I would recommend taking advantage of the amazing tooling that exists for Java and JVM languages. Modern IDEs like Eclipse and IntelliJ IDEA and build management tools like Maven or Gradle will help you not have to worry about classpaths (as much) and focus on the code! That said, this link explains how to set the classpath when you execute on the command line.

Exception in thread main java.lang.NoClassDefFoundError with NetBeans

See my answer of this i am sure that is Desired Solution. and if You sure 100% that there is exist same class which is shown in error.

This is my ans

Try it that will be helpful.

java error: Exception in thread main java.lang.NoClassDefFoundError

If you're referring to a jar file that should be on the classpath, you must name it explicitly. E.g.

java -cp "G:/java/helloworld;G:/whereever/algs4j.jar" HelloWorld

Do they really provide another name for System.out? In this case you can also safely ignore that jar by using System.out instead of StdOut

Exception in thread main java.lang.NoClassDefFoundError: Hello

In folder src/:

$ javac org/example/Hello.java
$ java org.example.Hello

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