java
NAME
java - Java interpreter
SYNOPSIS
java [ options ] class [ argument ... ]
java [ options ] -jar file.jar
[ argument ... ]
PARAMETERS
Options may be in any order. For a discussion of parameters which
apply to a specific option, see OPTIONS below.
options Command-line options. See OPTIONS below.
class Name of the class to be invoked.
file.jar Name of the jar file to be invoked. Used only with the
-jar option.
DESCRIPTION
The java utility launches a Java application. It does this by starting
a Java runtime environment, loading a specified class, and invoking
that class's main method. The method must have the following signature:
public static void main(String args[])
The method must be declared public and static, it must not return any
value, and it must accept a String array as a parameter. By default,
the first non-option argument is the name of the class to be invoked.
A fully-qualified class name should be used. If the -jar option is
specified, the first non-option argument is the name of a JAR archive
containing class and resource files for the application, with the
startup class indicated by the Main-Class manifest header.
The Java runtime searches for the startup class, and other classes
used, in three sets of locations: the bootstrap class path, the
installed extensions, and the user class path.
Non-option arguments after the class name or JAR file name are passed
to the main function.
OPTIONS
The launcher has a set of standard options that are supported on the
current runtime environment and will be supported in future releases.
However, options below that are described as having been replaced by
another one are obsolete and may be removed in a future release. An
additional set of nonstandard options are specific to the current virtual
machine implementation and are subject to change in the future.
Non-standard options begin with -X .
STANDARD OPTIONS
-client Selects the Java HotSpot Client VM.
Note: The exact form of the -client option may be modified in a future
release.
-classpath classpath
-cp classpath
Specifies a list of directories, JAR archives, and ZIP archives
to search for class files. Class path entries are separated by
colons (:). Specifying -classpath or -cp overrides any setting
of the CLASSPATH environment variable.
Used with java, the -classpath or -cp options only specify the
class path for user classes. If -classpath and -cp are not used
and CLASSPATH is not set, the user class path consists of the
current directory (.).
-debug This has been replaced by -Xdebug.
-Dproperty=value
Sets a system property value.
-enableassertions, -ea
-enableassertions:package-name "..."
-enableassertions:class-name
Enables assertions. Assertions are disabled by default.
With no arguments, -enableassertions or -ea enables assertions.
With one argument ending in "...", the switch enables assertions
in the specified package and any subpackages. If the argument is
simply "...", the switch enables assertions in the unnamed package
in the current working directory. With one argument not ending
in "...", the switch enables assertions in the specified
class.
If a single command line contains multiple instances of these
switches, the are processed in order before loading any classes.
So, for example, to run a program with assertions enabled only
in package com.wombat.fruitbat (and any subpackages), the following
command could be used:
example% java -ea:com.wombat.fruitbat... main_class
The -enableassertions and -ea switches apply to all class loaders
and to system classes (which do not have a class loader).
There is one exception to this rule: in their no-argument form,
the switches do not apply to system. This makes it easy to turn
on asserts in all classes except for system classes. A separate
switch is provided to enable asserts in all system classes. See
-enablesystemassertions below.
-disableassertions, -da
-disableassertions:package-name "..."
-disableassertions:class-name
Disables assertions. This is the default.
With no arguments, -disableassertions or -da disables assertions.
With one argument ending in "...", the switch disables
assertions in the specified package and any subpackages. If the
argument is simply "...", the switch disables assertions in the
unnamed package in the current working directory. With one argument
not ending in "...", the switch disables assertions in the
specified class.
To run a program with assertions enabled in package com.wombat.fruitbat
but disabled in class com.wombat.fruitbat.Brickbat,
the following command could be used:
example% java -ea:com.wombat.fruitbat...
-da:com.wombat.fruitbat.Brickbat main_class
The -disableassertions and -da switches apply to all class loaders
and to system classes (which do not have a class loader).
There is one exception to this rule: in their no-argument form,
the switches do not apply to system. This makes it easy to turn
off asserts in all classes except for system classes. A separate
switch is provided to disable asserts in all system classes. See
-disablesystemassertions below.
-enablesystemassertions, -esa
Enables asserts in all system classes (sets the default assertion
status for system classes to true).
-disablesystemassertions, -dsa
Disables asserts in all system classes.
-jar Executes a program encapsulated in a JAR archive. The first
argument is the name of a JAR file instead of a startup class
name. In order for this option to work, the manifest of the JAR
file must contain a line of the form Main-Class:classname.
Here, classname identifies the class having the public static
void main(String[] args) method that serves as your application's
starting point. See the Jar tool reference page and the
Jar trail of the Java Tutorial for information about working
with Jar files and Jar-file manifests. When you use this
option, the JAR file is the source of all user classes, and
other user class path settings are ignored.
-noclassgc
This has been replaced by -Xnoclassgc.
-msn This has been replaced by -Xms n.
-mxn This has been replaced by -Xmx n.
-ssn This has been replaced by -Xss n.
-verbose
-verbose:class
Displays information about each class loaded.
-verbosegc
This has been replaced by -verbose:gc.
-verbose:gc
Reports on each garbage collection event.
-verbose:jni
Reports information about use of native methods and other Java
Native Interface activity.
-version
Displays version information and exit.
-showversion
Displays version information and continues.
-?
-help Displays usage information and exit.
-X Displays information about non-standard options and exit.
NON-STANDARD OPTIONS
-Xint Operates in interpreted-only mode. Compilation to native code
is disabled, and all bytecodes are executed by the interpreter.
The performance benefits offered by the Java HotSpot VMs' adaptive
compiler will not be present in this mode.
-Xbootclasspath:bootclasspath
Specifies a colon-separated list of directories, JAR archives,
and ZIP archives to search for boot class files. These are used
in place of the boot class files included in the Java 2 SDK and
Java 2 Runtime Environment.
-Xbootclasspath/a:path
Specifies a colon-separated path of directories, JAR archives,
and ZIP archives to append to the default bootstrap class path.
-Xbootclasspath/p:path
Specifies a colon-separated path of directories, JAR archives,
and ZIP archives to prepend in front of the default bootstrap
class path. Note: Applications that use this option for the
purpose of overriding a class in the default bootstrap class
path should not be deployed, as doing so would contravene the
Java 2 Runtime Environment binary code license.
-Xdebug
Starts with the debugger enabled.
-Xfuture
Performs strict class-file format checks. For purposes of backwards
compatibility, the default format checks performed by the
Java 2 SDK's virtual machine are no stricter than the checks
performed by 1.1.x versions of the JDK software. The -Xfuture
flag turns on stricter class-file format checks that enforce
closer conformance to the class-file format specification.
Developers are encouraged to use this flag when developing new
code because the stricter checks will become the default in
future releases of the Java application launcher.
-Xnoclassgc
Disables class garbage collection
-Xmsn Specifies the initial size of the memory allocation pool. This
value must be greater than 1000. To modify the meaning of n,
append either the letter k for kilobytes or the letter m for
megabytes.
-Xmxn Specifies the maximum size of the memory allocation pool. This
value must be greater than 1000. To modify the meaning of n,
append either the letter k for kilobytes or the letter m for
megabytes.
-Xprof Profiles the running program, and sends profiling data to standard
output. This option is provided as a utility that is useful
in program development and is not intended to be be used in
production systems.
-Xrunhprof[:help][:suboption=value,...]
Enables cpu, heap, or monitor profiling. This option is typically
followed by a list of comma-separated suboption=value
pairs. Run the command java -Xrunhprof:help to obtain a list of
suboptions and their default values.
-Xssn Each Java thread has two stacks: one for Java code and one for C
code. The -Xss option sets the maximum stack size that can be
used by C code in a thread to n. Every thread that is spawned
during the execution of the program passed to java has n as its
C stack size. The default units for n are bytes and n must be >
1000 bytes.
To modify the meaning of n, append either the letter k for kilobytes
or the letter m for megabytes.
-Xrs Reduce usage of operating-system signals by Java virtual machine
(JVM).
The JVM catches signals to implement shutdown hooks for abnormal
JVM termination. The JVM uses SIGHUP, SIGINT, and SIGTERM to
initiate the running of shutdown hooks. The JVM uses SIGQUIT to
perform thread dumps.
Applications that embed the JVM frequently need to trap signals
like SIGINT or SIGTERM, and in such cases there is the possibility
of interference between the applications' signal handlers
and the JVM shutdown-hooks facility.
To avoid such interference, the -Xrs option can be used to turn
off the JVM shutdown-hooks feature. When -Xrs is used, the signal
masks for SIGINT, SIGTERM, SIGHUP, and SIGQUIT are not
changed by the JVM, and signal handlers for these signals are
not installed.
ENVIRONMENT VARIABLES
CLASSPATH
Used to provide the system with a path to user-defined classes.
Directories are separated by colons. For example:
.:/Users/vlh/classes:/Users/Shared/classes
SEE ALSO
javac(1), jdb(1), javac(1), jar(1)
See (or search java.sun.com) for the following:
JDK File Structure @
http://java.sun.com/j2se/1.4/docs/tooldocs/solaris/jdkfiles.html
Setting the Classpath @
http://java.sun.com/j2se/1.4/docs/tooldocs/solaris/classpath.html
JAR Files @
http://java.sun.com/docs/books/tutorial/jar/
NOTES
All the -X options are unstable. As noted in the OPTIONS section, some
of the "standard" options are obsolete.
3 May 2001 java(1)
