From Linux Man Pages
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-quali-
fied 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 boot-
strap 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 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 However, options below that are described as having been replaced by another one are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 additional 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 (:). Specifying -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-debug This has been replaced by -Xdebug.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 disabled by default.
With no arguments, enableassertions or -ea enable 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, they are processed in
order before loading any classes. So, for example, to run a program with assertions enabled
only in packagecom.wombat.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.wombat.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 system classes. A separate switch is provided 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 appli-
cation's starting point. See the Jar tool reference page and the Jar trail of the Java Tuto-
rial 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 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 encountered indicates a
problem in the native code, and the Java Virtual Machine will terminate with a fatal error in
such cases. Expect a performance 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 format checks that enforce closer conformance to the class-file format specifica-
tion. 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 collector. The incremental garbage collector, which is off by
default, will eliminate occasional garbage-collection pauses during program execution. How-
ever, 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 net-
work latency. The file may be truncated in the case of a full file system and logging will
continue on the truncated file. This option overrides -verbose:gc if both are given on the
command line.
-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. The default value is 2m.
-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. The default value is 64m. The uppoer limit for this value will be approxi-
mately 4000m on SPARC platforms and 2000m on x86 platforms, minus overhead amounts.
-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. The default stack size is determined by the Linux operating system upon which the
Java platform is running.
-Xrs Reduce usage of operating-system signals by Java virtual machine (JVM).
Sun's 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 han-
dlers 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:
.:/home/avh/classes:/usr/local/java/classes
RELATED
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/jdkfiles.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.
CATEGORY