The java.lang package contains the collection of base types (language types) that are always imported into any given compilation unit. This is where you'll find the declarations of
Object (the root of the class hierarchy) and
Class, plus threads, exceptions, wrappers for the primitive data types, and a variety of other fundamental classes.
This picture illustrates the classes in java.lang, excluding all the exception and error classes.
Note the
Boolean,
Character, and
Number classes--these classes are "wrapper" classes for the primitive types. You use these classes in applications where the primitive types must be stored as objects. Note also the
Throwable class--this is the root class for all exceptions and errors.
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