Kick Out Fundamentals: Difference between java.lang.NoClassDefFoundError and ClassNotFoundException in Java

Exception in thread "main" java.lang.NoClassDefFoundError

Many a times we confused ourselves with java.lang.ClassNotFoundException and java.lang.NoClassDefFoundError, though both of them related to Java Classpath they are completely different to each other.
ClassNotFoundException comes when JVM tries to load a class at runtime dynamically means you give the name of class at runtime and then JVM tries to load it and if that class is not found in classpath it throws java.lang.ClassNotFoundException.

While in case of NoClassDefFoundError the problematic class was present during Compile time and that's why program was successfully compile but not available during runtime by any reason.
NoClassDefFoundError is easier to solve than ClassNotFoundException in my opinion because here we know that Class was present during build time but it totally depends upon environment.
If you are working in J2EE environment than you can get NoClassDefFoundError even if class is present because it may not be visible to corresponding ClassLoader.