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

Example #1:

class A{
 void met(){
   Class.forName("com.example.Class1");
 }
}

If com/example/Class1 doesn't exist in any of the classpaths, then It throws ClassNotFoundException.

Example #2:

Class B{
  void met(){
   com.example.Class2 c = new com.example.Class2();
 }
}

If com/example/Class2 existed while compiling B, but not found while execution, then It throws NoClassDefFoundError.

Both are run time exceptions.