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java - Java application launcher
SYNOPSIS
java [ options ] class [ argument ... ]
java [ options ] -jar file.jar
[ argument ... ]
PARAMETERS
options Command-line options.
class Name of the class to be invoked.
file.jar Name of the jar file to be invoked. Used only with the -jar option.
argument Argument passed to the main function.
DESCRIPTION
The java tool launches a Java application. It does this by starting a Java runtime environment, loading a speci-
fied class, and invoking that class's main method. The method must be declared public and static , it must not
return any value, and it must accept a String array as a parameter. The method declaration must look like the
following:
public static void main(String args[])
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 con-
taining 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. In addition, the current impletmentations of the virtual machines support a set of
non-standard options that are subject to change in future releases.
Standard Options
-client Selects the Java HotSpot Client VM. For more information see Server-Class Machine Detection
at http://java.sun.com/j2se/1.5.0/docs/guide/vm/server-class.html
-server Selects the Java HotSpot Server VM. For more information see Server-Class Machine Detection
at http://java.sun.com/j2se/1.5.0/docs/guide/vm/server-class.html
-agentlib:libname[=options]
Load native agent library libname , e.g.,
-agentlib:hprof
-agentlib:jdwp=help
-agentlib:hprof=help
For more information, see JVMTI Agent Command Line Options at
http://java.sun.com/j2se.1.5.0/docs/guide/jvmti/jvmti.html
-agentpath:pathname[=options]
Load a native agent library by full pathname. For more information, see JVMTI Agent Command Line Options
at http://java.sun.com/j2se.1.5.0/docs/guide/jvmti/jvmti.html
-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 (.).
-Dproperty=value
Sets a system property value.
-d32
-d64 Specified whether the program is to be run in a 32-bit or 64-bit environment if available.
Currently, only the Java HotSpot Server VM supports 64-bit operations and the -server option is implicit with the
use of -d64 . This is subject to change in a future release.
If neither -d32 nor -d64 is specified, the default is to run in a 32-bit environment, except for 64-bit only sys-
tems. This is subject to change in a future release.
-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.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 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 Execute 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 man-
ifests.
When you use this option, the JAR file is the source of all user classes, and other user class path settings are
ignored.
Note that JAR files that can be run with the "java -jar" option can have their execute permissions set so they
can be run without using "java -jar". Refer to Java Archive (JAR) Files.
-javaagent:jarpath[=options]
Load a Java programming language agent, see java.lang.instrument.
-verbose
-verbose:class
Displays information about each class loaded.
-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.
-Xbatch Disable background compilation. Normally the VM will compile the method as a background task,
running the method in interpreter mode until the background compilation is finished. The
-Xbatch flag disables background compilation so that compilation of all methods proceeds as a
foreground task until completed.
-Xdebug Start with support for JVMDI enabled. JVMDI has been deprecated and is not used for debugging
in J2SE 5.0, so this option isn't needed for debugging in J2SE 5.0.
-Xbootclasspath:bootclasspath
Specify 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. 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.
-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.
-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 reduce the occasional garbage-collection pauses during program execution. The
incremental garbage collector will at times execute concurrently with the program and during
such times will reduce the processor capacity available to the program.
-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 a multiple of
1024 greater than 1 MB. Append the letter k or K to indicate kilobytes or the letter m or M
to indicate megabytes. The default value is 2MB. Examples:
-Xms6291456
-Xms6144k
-Xms6m
-Xmxn Specifies the maximum size, in bytes, of the memory allocation pool. This value must be a multiple of
1024 greater than 2 MB. Append the letter k or K to indicate kilobytes or the letter m or M to indicate
megabytes. The default value is 64MB. Examples:
-Xmx83886080
-Xmx81920k
-Xmx80m
On Solaris 7 and Solaris 8 SPARC platforms, the upper limit for this value is approximately 4000m minus overhead
amounts. On Solaris 2.6 and x86 platforms, the upper limit is approximately 2000m minus overhead amounts. On
Linux platforms, the upper limit is approximately 2000m 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.
-Xrs Reduce usage of operating-system signals by Java virtual machine (JVM).
n a previous release, the Shutdown Hooks facility was added to allow orderly shutdown of a Java applica-
tion. The intent was to allow user cleanup code (such as closing database connections) to run at shutdown,
even if the JVM terminates abruptly.
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 a similar mechanism to implement the pre-1.2 feature of dumping thread stacks for debugging
purposes. Sun's JVM uses SIGQUIT to perform thread dumps.
Applications that embed the JVM frequently need to trap signals like SIGINT or SIGTERM, which can lead to
interference with the JVM's own signal handlers. The -Xrs command line option is available to address this
issue. When -Xrs is used on Sun's JVM, the signal masks for SIGINT, SIGTERM, SIGHUP, and SIGQUIT are not
changed by the JVM, and signal handlers for these signals are not installed.
There are two conseguences of specifying -Xrs:
� SIGQUIT thread dumps are not available.
� User code is responsible for causing
shutdown hooks to run, for example by calling System.exit() when the JVM is to be terminated.
-Xssn
Set thread stack size. /TP -XX:+UseAltSigs The VM uses SIGUSR1 and SIGUSR2 by default, which can sometimes
conflict with applications that signal-chain SIGUSR1 and SIGUSR2. The -XX:+UseAltSigs option will cause the VM
to use signals other than SIGUSR1 and SIGUSR2 as the default.
RELATED
javac(1), jdb(1), javah(1), jar(1),
See (or search java.sun.com) for the following:
The Java Extensions Framework @
http://java.sun.com/j2se/1.5.0/docs/guide/extensions/index.html
Security Features @
http://java.sun.com/j2se/1.5.0/docs/guide/security/index.html
CATEGORY