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.

Package Specification

Character Encodings

Subpackages
java.lang.annotation
java.lang.instrument
java.lang.management
java.lang.ref
java.lang.reflect

Interfaces
Appendable
CharSequence
Cloneable
Comparable
Iterable
Readable
Runnable
  .UncaughtExceptionHandler

Annotations
Deprecated
Override
SuppressWarnings

Enumerations
  .State

Errors
AbstractMethodError
AssertionError
ClassCircularityError
ClassFormatError
Error
ExceptionInInitializerError
IllegalAccessError
IncompatibleClassChangeError
InstantiationError
InternalError
LinkageError

Exceptions
ArithmeticException
ArrayIndexOutOfBoundsException
ArrayStoreException
ClassCastException
ClassNotFoundException
CloneNotSupportedException
EnumConstantNotPresentException
Exception
IllegalAccessException
IllegalArgumentException
IllegalMonitorStateException
IllegalStateException
IllegalThreadStateException
IndexOutOfBoundsException
InstantiationException
InterruptedException
NegativeArraySizeException
NoSuchFieldException
NoSuchMethodException
NullPointerException
NumberFormatException
RuntimeException
SecurityException
StringIndexOutOfBoundsException
TypeNotPresentException
UnsupportedOperationException