java(1)

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 parame
ters 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 speci
fied, the first non-option argument is the name of a JAR
archive containing class and resource files for the appli
cation, 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 sup
ported on the current runtime environment and will be sup
ported 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are described as having been replaced by another one are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 addi
tional set of non-standard 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.

This is the default.

-server Selects the Java HotSpot Server VM.

-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 (:). Specify
ing -classpath or -cp overrides any setting of the CLASSPATH environment variable.

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-debug This has been replaced by -Xdebug.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 :<package name>... |:<class name> -ea :<package name>... |:<class name>

Enable assertions. Assertions are dis
abled by default.

With no arguments, enableassertions or -ea enable assertions. With one argu
ment 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 direc
tory. With one argument not ending in
"...", the switch enables assertions
in the specified class.

If a single command line contains mul
tiple instances of these switches,
they are processed in order before
loading any classes. So, for example,
to run a program with assertions
enabled only in packagecom.wom bat.fruitbat (and any subpackages),
the following command could be used:

java -ea:com.wombat.fruitbat... <Main
Class>

The -enableassertions and -ea switches apply to all s 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 :<package name>... |:<class;
-da :<package name>... |:<class name>

Disable 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 rent 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.wom bat.fruitbat.Brickbat, the following command could be used:

java -ea:com.wombat.fruitbat...
-da:com.wombat.fruitbat.Brickbat <Main
Class>

The -disableassertions and -da switches apply to all ss 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 sys
tem classes. A separate switch is pro
vided to enable asserts in all system
classes; see -disablesystemassertions below.

-enablesystemassertions
-esa Enable 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 infor
mation 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 con

tinues.

-?
-help Displays usage information and exit.

-X Displays information about non-stan

dard options and exit.

Non-Standard Options

-Xint Operates in interpreted-only mode.

Compilation to native code is dis
abled, 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
rt.jar should not be deployed, as doing so would contravene the Java 2
Runtime Environment binary code
license.

-Xcheck:jni Perform additional checks for Java

Native Interface (JNI) functions.
Specifically, the Java Virtual Machine
validates the parameters passed to the
JNI function as well as the runtime
environment data before processing the
JNI request. Any invalid data encoun
tered indicates a problem in the
native code, and the Java Virtual
Machine will terminate with a fatal
error in such cases. Expect a perfor
mance degradation when this option is
used.

-Xdebug Starts with the debugger enabled.

-Xcheck:jni Perform additional check for Java

Native Interface functions.

-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 for
mat checks that enforce closer confor
mance to the class-file format speci
fication. 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

-Xincgc Enable the incremental garbage collec

tor. The incremental garbage collec
tor, which is off by default, will
eliminate occasional garbage-collec
tion pauses during program execution.
However, it can lead to a roughly 10%
decrease in overall GC performance.

-Xloggc: file Report on each garbage collection

event, as with -verbose:gc, but log this data to file . In addition to
the information -verbose:gc gives, each reported event will be preceeded
by the time (in seconds) since the
first garbage-collection event.

Always use a local file system for
storage of this file to avoid stalling
the JVM due to network latency. The
file may be truncated in the case of a
full file system and logging will con
tinue on the truncated file. This
option overrides -verbose:gc if both are given on the command line.

-Xmsn Specifies the initial size of the mem

ory 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. The default value is 2m.

-Xmxn Specifies the maximum size of the mem

ory 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. The default value is 64m.
The uppoer limit for this value will
be approximately 4000m on SPARC plat
forms and 2000m on x86 platforms,
minus overhead amounts.

-Xprof Profiles the running program, and

sends profiling data to standard out
put. 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 profil
ing. This option is typically fol
lowed by a list of comma-separated
suboption=value pairs. Run the com mand 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. The
default stack size is determined by
the Linux operating system upon which
the Java platform is running.

-Xrs Reduce usage of operating-system sig

nals by Java virtual machine (JVM).

Sun's JVM catches signals to implement
shutdown hooks for abnormal JVM termi
nation. 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 fre
quently need to trap signals like SIG
INT or SIGTERM, and in such cases
there is the possibility of interfer
ence 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 han
dlers 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:

.:/home/avh/classes:/usr/local/java/classes

SEE ALSO

javac(1), jdb(1), javac(1), jar(1), set(1)

See (or search java.sun.com) for the following:

JDK File Structure @

http://java.sun.com/j2se/1.4/docs/tooldocs/linux/jdk
files.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.

16 Sep 2002 java(1)