Under certain conditions, custom exceptions that are not predefined in C++ may be useful to generate. In C++, any type can be caught or thrown that matches some requirements. These are that the type should have a valid copy constructor and destructor. Custom exceptions provide relevant information about an error to the exception handling mechanism.

The CloneNotSupportedException is an exception in Java that is thrown to indicate that the clone() method in class Object was called to clone an object, but that object's class does not implement the Cloneable interface. Applications that override the clone() method can also throw this exception to indicate that an object could not or should not be cloned.

The InstantiationException is a runtime exception in Java that occurs when an application attempts to create an instance of a class using the Class.newInstance() method, but the specified class object cannot be instantiated. Since the InstantiationException is an unchecked exception, it does not need to be declared in the throws clause of a method or constructor.