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.
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Built in functions in java are methods that are present in different API of JDK . For example cos(double a), exp(double a) etc are built in function of java present in java. lang. Math class.
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