How do I fix a NoSuchMethodError?

I'm getting a NoSuchMethodError error when running my Java program. What's wrong and how do I fix it?

Without any more information it is difficult to pinpoint the problem, but the root cause is that you most likely have compiled a class against a different version of the class that is missing a method, than the one you are using when running it.

Look at the stack trace ... If the exception appears when calling a method on an object in a library, you are most likely using separate versions of the library when compiling and running. Make sure you have the right version both places.

If the exception appears when calling a method on objects instantiated by classes you made, then your build process seems to be faulty. Make sure the class files that you are actually running are updated when you compile.

I was having your problem, and this is how I fixed it. The following steps are a working way to add a library. I had done the first two steps right, but I hadn't done the last one by dragging the ".jar" file direct from the file system into the "lib" folder on my eclipse project. Additionally, I had to remove the previous version of the library from both the build path and the "lib" folder.

Step 1 - Add .jar to build path

Step 2 - Associate sources and javadocs (optional)

Step 3 - Actually drag .jar file into "lib" folder (not optional)

Note that in the case of reflection, you get an NoSuchMethodException, while with non-reflective code, you get NoSuchMethodError. I tend to go looking in very different places when confronted with one versus the other.

If you have access to change the JVM parameters, adding verbose output should allow you to see what classes are being loaded from which JAR files.

java -verbose:class <other args>

When your program is run, the JVM should dump to standard out information such as:

...

[Loaded junit.framework.Assert from file:/C:/Program%20Files/junit3.8.2/junit.jar]

...