Enpatika

A built-in class is a class whose instances have restricted capabilities or special representations . Attempting to use defclass to define subclasses of a built-in class signals an error of type error. Calling make-instance to create an instance of a built-in class signals an error of type error.

In Java, all classes (built-in or user-defined) are (implicitly) subclasses of Object . Using an array of Object in the List class allows any kind of Object (an instance of any class) to be stored in the list. However, primitive types (int, char, etc) cannot be stored in the list.