JAVA Quick Reference
Author: Jialong He
Jialong_he@bigfoot.com
http://www.bigfoot.com/~jialong_he
Simple Data Types
byte 8 -128..127
short 16 -32,768..32,767
int 32 -2,147,483,648.. 2,147,483,647
long 64 -9,223,372,036,854,775,808..
9,223,372,036,854,775,807
float 32 3.4e-0.38.. 3.4e+0.38
double 64 1.7e-308.. 1.7e+308
char 16 Complete Unicode Character Set
Boolean true, false
decare a variable:
type identifier [= value];
Arrays
int array_name[ ];
array_name=new int[100 ];
declare an integer array and allocate
100 elements of memory.
int array_name[ ] = new int [
100];
int array_name [ ] = {1, 2, 3, 4};
declare and allocate an integer array in
one statement.
int array_name[] = new
int[10][20];
multidimensional array.
null for reference type (class, array).
Class
{public|final|abstract} class name
{ [class_variable_declarations]
public static void main{String[] args) {statements}
[methods]
}
this, super
Methods
{public| private} [static] {type | void} name(arg, ..., arg ) {statements}
Variable
{public| private} [static] type name [= expression];
Arithmetic Operators
+, -, *, /
%, ++, --
addition, subtraction, multiplication, division
modulus, increment, decrement.
Relational Operators
==, !=, >, <,
>=, <=
equal, not equal, greater, less,
greater or equal, less or equal.
Logical Operators
&, |, !, ^, ||, &&, AND, OR, NOT, XOR, short -circuit OR, AND
Bitwise Operators
&, |, ~, ^,
>>, >>>, <<
AND, OR, NOT, XOR
shift right, shift right zero fill, shift left.
Comments
// rest of line
/* multiline comment */
/** documentation comment */
Compile and Run
javac nameOfFile.java
java nameOfFile
CLASSPATH must set correctly.
The name of the file has to match exactly the name of the class.
Flow Control
if (Boolean-expression) statement1; [ else statement2; ]
while loop
[initialization]
while (termination-clause) {
body;
[iteration;]
}
do while loop
do {
body;
[iteration;]
} while (termination-clause);
for loop
for (initialization; termination-clause; iteration)
body;
Program Structure
class className {
public static void main (String args[ ]) {
statements;
}
method definition1
...
method definitionN
}
Key words
abstract boolean break byte byvalue
case cast catch char class
const continue default do double
else extends false final finally
float for future generic goto
if implements import inner instanceof
int interface long native new
null operator outer package private
protected public rest return short
static super switch synchronized this
throw throws transient true try
var void volatile while
Java packages
java.applet Provides the classes necessary to create an applet
and the classes an applet uses to communicate with
its applet context.
java.awt Contains all of the classes for creating user
interfaces and for painting graphics and images.
java.awt.color Provides classes for color spaces.
java.awt.datatransfe
r
Provides interfaces and classes for transferring data
between and within applications.
java.awt.dnd Drag and Drop is a direct manipulation gesture
found in many Graphical User Interface systems
that provides a mechanism to transfer information
between two entities logically associated with
presentation elements in the GUI.
java.awt.event Provides interfaces and classes for dealing with
different types of events fired by AWT
components.
java.awt.font Provides classes and interface relating to fonts.
java.awt.geom Provides the Java 2D classes fordefining and
performing operations on objects related to twodimensional
geometry.
java.awt.im Provides classes and interfaces for the input method
framework.
java.awt.im.spi Provides interfaces that enable the development of
input methods that can be used with any Java
runtime environment.
java.awt.image Provides classes for creating and modifying
images.
java.awt.image.rend
erable
Provides classes and interfaces for producing
rendering-independent images.
java.awt.print Provides classes and interfaces for a general
printing API.
java.beans Contains classes related to developing beans --
components based on the JavaBeansTM
architecture.
java.beans.beancont
ext
Provides classes and interfaces relating to bean
context.
java.io Provides for system input and output through data
streams, serialization and the file system.
java.lang Provides classes that are fundamental to the design
of the Java programming language.
java.lang.ref Provides reference-object classes, which support a
limited degree of interaction with the garbage
collector.
java.lang.reflect Provides classes and interfaces for obtaining
reflective information about classes and objects.
java.math Provides classes for performing arbitrary-precision
integer arithmetic (BigInteger) and arbitraryprecision
decimal arithmetic (BigDecimal).
java.net Provides the classes for implementing networking
applications.
java.nio Defines buffers, which are containers for data, and
provides an overview of the other NIO packages.
java.nio.channels Defines channels, which represent connections to
entities that are capable of performing I/O
operations, such as files and sockets; defines
selectors, for multiplexed, non-blocking I/O
operations.
java.nio.channels.spi Service-provider classes for the
java.nio.channels package.
java.nio.charset Defines charsets, decoders, and encoders, for
translating between bytes and Unicode characters.
java.nio.charset.spi Service-provider classes for the java.nio.charset
package.
java.rmi Provides the RMI package.
java.rmi.activation Provides support for RMI Object Activation.
java.rmi.dgc Provides classes and interface for RMI distributed
garbage-collection (DGC).
java.rmi.registry Provides a class and two interfaces for the RMI
registry.
java.rmi.server Provides classes and interfaces for supporting the
server side of RMI.
java.security Provides the classes and interfaces for the security
framework.
java.security.acl The classes and interfaces in this package have
been superseded by classes in the java.security
package.
java.security.cert Provides classes and interfaces for parsing and
managing certificates, certificate revocation lists
(CRLs), and certification paths.
java.security.interfa
ces
Provides interfaces for generating RSA (Rivest,
Shamir and Adleman AsymmetricCipher
algorithm) keys as defined in the RSA Laboratory
Technical Note PKCS#1, and DSA (Digital
Signature Algorithm) keys as defined in NIST's
FIPS-186.
java.security.spec Provides classes and interfaces for key
specifications and algorithm parameter
specifications.
java.sql Provides the API for accessing and processing data
stored in a data source (usually a relational
database) using the JavaTM
programming language.
java.text Provides classes and interfaces for handling text,
dates, numbers, and messages in a manner
independent of natural languages.
java.util Contains the collections framework, legacy
collection classes, event model, date and time
facilities, internationalization, and miscellaneous
utility classes (a string tokenizer, a random-number
generator, and a bit array).
java.util.jar Provides classes for reading and writing the JAR
(Java ARchive) file format, which is based on the
standard ZIP file format with an optional manifest
file.
java.util.logging Provides the classes and interfaces of the JavaTM
2
platform's core logging facilities.
java.util.prefs This package allows applications to store and
retrieve user and system preference and
configuration data.
java.util.regex Classes for matching character sequences against
patterns specified by regular expressions.
java.util.zip Provides classes for readingand writing the
standard ZIP and GZIP file formats.
Java extension packages
javax.accessibility Defines a contract between user-interface
components and an assistive technology that
provides access to those components.
javax.crypto Provides the classes and interfaces for
cryptographic operations.
javax.crypto.interfa
ces
Provides interfaces for Diffie-Hellman keys as
defined in RSA Laboratories' PKCS #3.
javax.crypto.spec Provides classes and interfaces for key
specifications and algorithm parameter
specifications.
javax.imageio The main package of the Java Image I/O API.
javax.imageio.event A package of the Java Image I/O API dealing with
synchronous notification of events during the
reading and writing of images.
javax.imageio.metad
ata
A package of the Java Image I/O API dealing with
reading and writing metadata.
javax.imageio.plugin
s.jpeg
Classes supporting the built -in JPEG plug-in.
javax.imageio.spi A package of the Java Image I/O API containing
the plug-in interfaces for readers, writers,
transcoders, and streams, and a runtime registry.
javax.imageio.strea
m
A package of the Java Image I/O API dealing with
low-level I/O from files and streams.
javax.naming Provides the classes and interfaces for accessing
naming services.
javax.naming.direct
ory
Extends the javax.naming package to provide
functionality for accessing directory services.
javax.naming.event Provides support for event notification when
accessing naming and directory services.
javax.naming.ldap Provides support for LDAPv3 extended operations
and controls.
javax.naming.spi Provides the means for dynamically plugging in
support for accessing naming and directory services
through the javax.naming and related packages.
javax.net Provides classes for networking applications.
javax.net.ssl Provides classes for the secure socket package.
javax.print Provides the principal classes and interfaces for the
JavaTM Print Service API.
javax.print.attribute Provides classes and interfaces that describe the
types of JavaTM Print Service attributes and how
they can be collected into attribute sets.
javax.print.attribute
.standard
Package javax.print.attribute.standard contains
classes for specific printing attributes.
javax.print.event Package javax.print.event contains event classes
and listener interfaces.
javax.rmi Contains user APIs for RMI-IIOP.
javax.rmi.CORBA Contains portability APIs for RMI-IIOP.
javax.security.auth This package provides a framework for
authentication and authorization.
javax.security.auth.c
allback
This package provides the classes necessary for
services to interact with applications in order to
retrieve information (authentication data including
usernames or passwords, for example) or to display
information (error and warning messages, for
example).
javax.security.auth.
kerberos
This package contains utility classes related to the
Kerberos network authentication protocol.
javax.security.auth.l
ogin
This package provides a pluggable authentication
framework.
javax.security.auth.s
pi
This package provides the interface to be used for
implementing pluggable authentication modules.
javax.security.auth.
x500
This package contains the classes that should be
used to store X500 Principal and X500 Private
Crendentials in a Subject.
javax.security.cert Provides classes for public key certificates.
javax.sound.midi Provides interfaces and classes for I/O, sequencing,
and synthesis of MIDI (Musical Instrument Digital
Interface) data.
javax.sound.midi.spi Supplies interfaces for service providers to
implement when offering new MIDI devices, MIDI
file readers and writers, or sound bank readers.
javax.sound.sample
d
Provides interfaces and classes for capture,
processing, and playback of sampled audio data.
javax.sound.sample
d.spi
Supplies abstract classes for service providers to
subclass when offering new audio devices, sound
file readers and writers, or audio format converters.
javax.sql Provides the API for server side data source access
and processing from the JavaTM programming
language.
javax.swing Provides a set of "lightweight" (all-Java language)
components that, to the maximum degree possible,
work the same on all platforms.
javax.swing.border Provides classes and interface for drawing
specialized borders around a Swing component.
javax.swing.colorch
ooser
Contains classes and interfaces used by the
JColorChooser component.
javax.swing.event Provides for events fired by Swing components.
javax.swing.filechoo
ser
Contains classes and interfaces used by the
JFileChooser component.
javax.swing.plaf Provides one interface and many abstract classes
that Swing uses to provide its pluggable look-andfeel
capabilities.
javax.swing.plaf.bas
ic
Provides user interface objects built according to
the Basic look and feel.
javax.swing.plaf.met
al
Provides user interface objects built according to
the Java look and feel (once codenamed Metal),
which is the default look and feel.
javax.swing.plaf.mul
ti
Provides user interface objects that combine two or
more look and feels.
javax.swing.table Provides classes and interfaces for dealing with
javax.swing.JTable.
javax.swing.text Provides classes and interfaces that deal with
editable and noneditable text components.
javax.swing.text.htm
l
Provides the class HTMLEditorKit and supporting
classes for creating HTML text editors.
javax.swing.text.htm
l.parser
Provides the default HTML parser, along with
support classes.
javax.swing.text.rtf Provides a class (RTFEditorKit) for creating RichText-Format
text editors.
javax.swing.tree Provides classes and interfaces for dealing with
javax.swing.JTree.
javax.swing.undo Allows developers to provide support for undo/redo
in applications such as text editors.
javax.transaction Contains three exceptions thrown by the ORB
machinery during unmarshalling.
javax.transaction.xa Provides the API that defines the contract between
the transaction manager and the resource manager,
which allows the transaction manager to enlist and
delist resource objects (supplied by the resource
manager driver) in JTA transactions.
javax.xml.parsers Provides classes allowing the processing of XML
documents.
javax.xml.transform This package defines the generic APIs for
processing transformation instructions, and
performing a transformation from source to result.
javax.xml.transform
.dom
This package implements DOM-specific
transformation APIs.
javax.xml.transform
.sax
This package implements SAX2-specific
transformation APIs.
javax.xml.transform
.stream
This package implements stream- and URIspecific
transformation APIs.