Understanding NoClassDefFoundError in Java


If you are a Java developer, you may have encountered a NoClassDefFoundError at some point in your career. This error is a common issue in Java applications and can be quite frustrating to debug. In this article, we will explore what a NoClassDefFoundError is, what causes it, and how to solve it.

What is NoClassDefFoundError?

NoClassDefFoundError is a runtime error that occurs when the Java Virtual Machine (JVM) cannot find a particular class at runtime, even though it was available during compile time. This error typically occurs when the JVM tries to load a class that was referenced in the code, but is not available in the classpath.

Common Causes of NoClassDefFoundError

There are a few common scenarios that can cause a NoClassDefFoundError:

  • The required class or jar file is not in the classpath
  • The classpath is misconfigured
  • The class is being loaded by a different classloader
  • There is a version mismatch between the compiled code and the runtime environment

How to Solve NoClassDefFoundError

Now that we understand the causes of NoClassDefFoundError, let's explore some possible solutions:

1. Check the Classpath

The first step in solving a NoClassDefFoundError is to verify that the required class or jar file is in the classpath. The classpath is a parameter that tells the JVM where to look for classes and resources. To check the classpath, you can print its value using the following code:


If you find that the required class or jar file is missing from the classpath, you can add it using the "-classpath" or "-cp" command line option, or by setting the CLASSPATH environment variable.

2. Verify the Classpath Configuration

If the required class or jar file is in the classpath, but you are still getting a NoClassDefFoundError, then the classpath configuration may be incorrect. Make sure that you have specified the correct paths and that any environment variables or system properties are correctly set.

3. Check for Class Loader Issues

In some cases, a NoClassDefFoundError can occur when a class is loaded by a different classloader than the one that loaded the class it depends on. This can happen when you have multiple classloaders in your application, or when you are using a framework or container that uses its own classloader. In such cases, you may need to adjust your classloader configuration to ensure that the required classes are loaded by the correct classloader.

4. Update the Runtime Environment

If you are getting a NoClassDefFoundError due to a version mismatch between the compiled code and the runtime environment, you may need to update the runtime environment to a compatible version. Make sure that you are running the correct version of Java, and that any libraries or dependencies are also compatible with the runtime environment.


NoClassDefFoundError is a common issue in Java applications, but it can be solved by checking the classpath, verifying the classpath configuration, addressing class loader issues, and updating the runtime environment if necessary. By following these steps, you should be able to fix the NoClassDefFoundError and get your Java application running smoothly again.