java.lang.package.html Maven / Gradle / Ivy
Provides classes that are fundamental to the design of the Java
programming language. The most important classes are 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.
Package Specification
Character Encodings
Various constructors and methods in the {@link java.lang} and {@link java.io}
packages accept string arguments that specify the character encoding to be used
when converting between raw eight-bit bytes and sixteen-bit Unicode characters.
Such encodings are named by strings composed of the following characters:
- The uppercase letters 'A' through 'Z'
('\u0041' through '\u005a'),
- The lowercase letters 'a' through 'z'
('\u0061' through '\u007a'),
- The digits '0' through '9'
('\u0030' through '\u0039'),
- The dash character '-'
('\u002d', HYPHEN-MINUS),
- The colon character ':'
('\u003a', COLON), and
- The underscore character '_'
('\u005f', LOW LINE).
An encoding name must begin with either a letter or a digit. The empty string
is not a legal encoding name.
An encoding may have more than one name. One of an encoding's names is
considered to be its canonical name. The canonical name of an encoding
is the name returned by the getEncoding methods of the {@link
java.io.InputStreamReader#getEncoding InputStreamReader} and {@link
java.io.OutputStreamWriter#getEncoding OutputStreamWriter} classes.
Encoding names generally follow the conventions documented in RFC2278: IANA Charset
Registration Procedures. If an encoding listed in the IANA Charset
Registry is supported by an implementation of the Java platform then one of
its names must be the name listed in the registry. Many encodings are given
more than one name in the registry, in which case the registry identifies one
of the names as MIME-preferred. An implementation of the Java platform
must support the MIME-preferred registry name for a supported encoding if there
is one; for convenience it may additionally support other registry names. The
IANA MIME-preferred name of an encoding, if there is one, is often, but not
necessarily, its canonical name. Following IANA convention, the mapping from
IANA registry names to encodings is not case-sensitive.
Every implementation of the Java platform is required to support the
following character encodings. Consult the release documentation for your
implementation to see if any other encodings are supported.
US-ASCII
Seven-bit ASCII, a.k.a. ISO646-US,
a.k.a. the Basic Latin block of the Unicode character set ISO-8859-1
ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1 UTF-8
Eight-bit Unicode Transformation Format UTF-16BE
Sixteen-bit Unicode Transformation Format,
big-endian byte order UTF-16LE
Sixteen-bit Unicode Transformation Format,
little-endian byte order UTF-16
Sixteen-bit Unicode Transformation Format,
byte order specified by a mandatory initial byte-order mark
(either order accepted on input, big-endian used on output)
The various Unicode Transformation Formats are described in detail in The Unicode
Standard and in the Unicode FAQ.
Every instance of the Java virtual machine has a default character
encoding. The default encoding is determined during virtual-machine startup
and typically depends upon the locale and encoding being used by the underlying
operating system.
@since JDK1.0