Object
,
which is the root of the class hierarchy, and Class
, instances of
which represent classes at run time.
Frequently it is necessary to represent a value of primitive type as
if it were an object. The wrapper classes Boolean
,
Character
, Integer
, Long
, Float
, and
Double
serve this purpose. An object of type Double
,
for example, contains a field whose type is double, representing that
value in such a way that a reference to it can be stored in a variable
of reference type. These classes also provide a number of methods for
converting among primitive values, as well as supporting such
standard methods as equals and hashCode. The Void
class is a
non-instantiable class that holds a reference to a Class
object
represening the primitive type void.
The class Math
provides commonly used mathematical functions such
as sine, cosine, and square root. The classes String
and
StringBuffer
similarly provide commonly used operations on
character strings.
Classes ClassLoader
, Process
, Runtime
,
SecurityManager
, and System
provide "system operations"
that manage the dynamic loading of classes, creation of external processes,
host environment inquiries such as the time of day, and enforcement of
security policies.
Class Throwable
encompasses objects that may be thrown by the
throw statement (§14.16). Subclasses of Throwable
represent errors
and exceptions.
@since JDK1.0