What causes and what are the differences between NoClassDefFoundError and ClassNotFoundException?

Question

What is the difference between NoClassDefFoundError and ClassNotFoundException?

What causes them to be thrown? How can they be resolved?

Answer 1

Add one possible reason in practise:

• ClassNotFoundException: as cletus said, you use interface while inherited class of interface is not in the classpath. E.g, Service Provider Pattern (or Service Locator) try to locate some non-existing class
• NoClassDefFoundError: given class is found while the dependency of given class is not found

In practise, Error may be thrown silently, e.g, you submit a timer task and in the timer task it throws Error, while in most cases, your program only catches Exception. Then the Timer main loop is ended without any information. A similar Error to NoClassDefFoundError is ExceptionInInitializerError, when your static initializer or the initializer for a static variable throws an exception.