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JAVA

Launches a Java application.


SYNOPSIS

java [ options ] class [ arguments ]

java [ options ] -jar file.jar [ arguments ]

javaw [ options ] class [ arguments ]

javaw [ options ] -jar file.jar [ arguments ]

options

Command-line options. See Options.

class

The name of the class to be called.

file.jar

The name of the JAR file to be called. Used only with the -jar command.

arguments

The arguments passed to the main function.


DESCRIPTION

The java command starts a Java application. It does this by starting a Java
runtime environment, loading a specified class, and calling 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 has the
following form:

public static void main(String[] args)


By default, the first argument without an option is the name of the class to be
called. A fully qualified class name should be used. If the -jar option is
specified, then the first non-option argument is the name of a JAR file
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.

The javaw command is identical to java, except that with javaw there is no
associated console window. Use javaw when you do not want a command prompt
window to appear. The javaw launcher will, however, display a dialog box with
error information if a launch fails for some reason.


OPTIONS

The launcher has a set of standard options that are supported in the current
runtime environment.

In addition, the default Java HotSpot VMs provide a set of non-standard options
that are subject to change in future releases. See Nonstandard Options.


STANDARD OPTIONS

-client

Selects the Java HotSpot Client VM. A 64-bit capable JDK currently ignores this
option and instead uses the Java Hotspot Server VM.

For default Java VM selection, see the Server-Class Machine Detection page at
http://docs.oracle.com/javase/7/docs/technotes/guides/vm/server-class.html

-server

Selects the Java HotSpot Server VM. On a 64-bit capable JDK, only the Java
Hotspot Server VM is supported so the -server option is implicit.

For default a Java VM selection, see the Server-Class Machine Detection page at
http://docs.oracle.com/javase/7/docs/technotes/guides/vm/server-class.html

-agentlib:libname[=options]

Loads native agent library libname, for example:

-agentlib:hprof
 
-agentlib:jdwp=help
 
-agentlib:hprof=help


See JVMTI Agent Command-Line Options at
http://docs.oracle.com/javase/7/docs/platform/jvmti/jvmti.html#starting

-agentpath:pathname[=options]

Loads a native agent library by full pathname.

-classpath classpath -cp classpath

Specifies a list of directories, JAR files, and ZIP archives to search for class
files. Separate class path entries with semicolons (;). Specifying -classpath or
-cp overrides any setting of the CLASSPATH environment variable.

If -classpath and -cp are not used and CLASSPATH is not set, then the user class
path consists of the current directory (.).

As a special convenience, a class path element that contains a base name of * is
considered equivalent to specifying a list of all the files in the directory
with the extension .jar or .JAR. A Java program cannot tell the difference
between the two invocations.

For example, if directory mydir contains a.jar and b.JAR, then the class path
element mydir/* is expanded to a A.jar:b.JAR, except that the order of jar files
is unspecified. All jar files in the specified directory, even hidden ones, are
included in the list. A class path entry consisting simply of * expands to a
list of all the jar files in the current directory. The CLASSPATH environment
variable, where defined, will be similarly expanded. Any class path wildcard
expansion occurs before the Java VM is started. No Java program will ever see
wild cards that are not expanded except by querying the environment. For
example, by calling System.getenv("CLASSPATH").

-Dproperty=value

Sets a system property value.

If value is a string that contains spaces, then you must enclose the string in
double quotation marks:

java -Dmydir="some string" SomeClass


-disableassertions[:package name"..." | :class name ] -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 "...", then 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:

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 on asserts in all classes except for system classes. The
-disablesystemassertions option provides a separate swith to enable assertions
in all system classes.

-enableassertions[:package name"..." | :class name ] -ea[:package name"..." |
:class name ]

Enable 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 "...", then 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 contains multiple instances of these switches, then they 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:

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. The
-enablesystemassertions option provides a separate switch to enable assertions
in all system classes.

-enablesystemassertions -esa

Enable assertions in all system classes (sets the default assertion status for
system classes to true).

-disablesystemassertions -dsa

Disables assertions in all system classes.

-help or -?

Displays usage information and exit.

-jar

Executes a program encapsulated in a JAR file. The first argument is the name of
a JAR file instead of a startup class name. For this option to work, the
manifest of the JAR file must contain a line in the form Main-Class: classname.
Here, classname identifies the class with the public static void main(String[]
args) method that serves as your application's starting point.

When you use this option, the JAR file is the source of all user classes, and
other user class path settings are ignored.

-javaagent:jarpath[=options]

Loads a Java programming language agent. For more information about
instrumenting Java applications, see the java.lang.instrument package
description in the Java API documentation at
http://docs.oracle.com/javase/7/docs/api/java/lang/instrument/package-summary.html

-jre-restrict-search

Includes user-private JREs in the version search.

-no-jre-restrict-search

Excludes user-private JREs in the version search.

-showversion

Displays version information and continue. (See also -version.)

-splash:imagepath

Shows splash screen with image specified by imagepath.

-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. See also the -showversion option.

-version:release

Specifies that the version specified by the release is required by the class or
JAR file specified on the command line. If the version of the java command
called does not meet this specification and an appropriate implementation is
found on the system, then the appropriate implementation will be used.

The release option specifies an exact version and a list of versions called a
version string. A version string is an ordered list of version ranges separated
by spaces. A version range is either a version-id, a version-id followed by an
asterisk (*), a version-id followed by a plus sign (+), or a version range that
consists of two version-ids combined using an ampersand (&). The asterisk means
prefix match, the plus sign means this version or greater, and the ampersand
means the logical and of the two version-ranges, for example:

-version:"1.6.0_13 1.6*&1.6.0_10+"


The meaning of the previous example is that the class or JAR file requires
either version 1.6.0_13, or a version with 1.6 as a version-id prefix and that
is not less than 1.6.0_10. The exact syntax and definition of version strings
can be found in Appendix A of the Java Network Launching Protocol & API
Specification (JSR-56).

For JAR files, the preference is to specify version requirements in the JAR file
manifest rather than on the command line.

See Notes for important policy information on the use of this option.


NONSTANDARD OPTIONS

-X

Displays information about nonstandard options and exits.

-Xint

Operates in interpreted-only mode. Compilation to native code is disabled, and
all bytecode is executed by the interpreter. The performance benefits offered by
the Java HotSpot VM client adaptive compiler is not present in this mode.

-Xbatch

Disables background compilation. Typically, the Java VM compiles 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.

-Xbootclasspath:bootclasspath

Specifies a semicolon-separated list of directories, JAR files, and ZIP archives
to search for boot class files. These are used in place of the boot class files
included in the Java platform JDK.

Applications that use this option for the purpose of overriding a class in
rt.jar should not be deployed because doing so would contravene the Java Runtime
Environment binary code license.

-Xbootclasspath/a:path

Specifies a semicolon-separated path of directories, JAR files, and ZIP archives
to append to the default bootstrap class path.

-Xbootclasspath/p:path

Specifies a semicolon-separated path of directories, JAR files, and ZIP archives
to add in front of the default bootstrap class path.

Do not deploy applications that use this option to override a class in rt.jar
because this violates the Java Runtime Environment binary code license.

-Xcheck:jni

Performs additional checks for Java Native Interface (JNI) functions.
Specifically, the Java Virtual Machine validates the parameters passed to the
JNI function and 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 backward compatibility, the
default format checks performed by the Java virtual machine are no stricter than
the checks performed by 1.1.x versions of the JDK software. The -Xfuture option
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. Use of this option preven memory recovery
from loaded classes thus increasing overall memory usage. This could cause
OutOfMemoryError to be thrown in some applications.

-Xincgc

Enables the incremental garbage collector. The incremental garbage collector,
which is turned off by default, will reduce the occasional long
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

Reports on each garbage collection event, as with -verbose:gc, but logs this
data to a file. In addition to the information -verbose:gc gives, each reported
event will be preceded 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
Java VM due to network 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 when both are specified on the command line.

-Xmnsize or -XX:NewSize

Sets the size of the young generation (nursery).

-Xmsn

Specifies the initial size, in bytes, 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 m or M to indicate megabytes. The default value is chosen
at runtime based on system configuration. See Garbage Collector Ergonomics at
http://docs.oracle.com/javase/7/docs/technotes/guides/vm/gc-ergonomics.html

Examples:

-Xms6291456
-Xms6144k
-Xms6m


-Xmxn

Specifies the maximum size, in bytes, of the memory allocation pool. This value
must a multiple of 1024 greater than 2 MB. Append the letter k or K to indicate
kilobytes, or m or M to indicate megabytes. The default value is chosen at
runtime based on system configuration.

For server deployments, -Xms and -Xmx are often set to the same value. See
Garbage Collector Ergonomics at
http://docs.oracle.com/javase/7/docs/technotes/guides/vm/gc-ergonomics.html

Examples:

-Xmx83886080
-Xmx81920k
-Xmx80m


-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 used in production systems.

-Xrs

Reduces use of operating-system signals by the Java VM.

In an earlier release, the Shutdown Hooks facility was added to enable orderly
shutdown of a Java application. The intent was to enable user cleanup code (such
as closing database connections) to run at shutdown, even if the Java VM
terminates abruptly.

The Java VM watches for console control events to implement shutdown hooks for
unexpected Java VM termination. Specifically, the Java VM registers a console
control handler which begins shutdown-hook processing and returns TRUE for
CTRL_C_EVENT, CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT, and CTRL_SHUTDOWN_EVENT.

The JVM uses a similar mechanism to implement the feature of dumping thread
stacks for debugging purposes. The JVM uses CTRL_BREAK_EVENT to perform thread
dumps.

If the Java VM is run as a service (for example, the servlet engine for a web
server), then it can receive CTRL_LOGOFF_EVENT but should not initiate shutdown
because the operating system will not actually terminate the process. To avoid
possible interference such as this, the -Xrs command-line option was added
beginning with J2SE 1.3.1. When the -Xrs option is used on the Java VM, the Java
VM does not install a console control handler, implying that it does not watch
for or process CTRL_C_EVENT, CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT, or
CTRL_SHUTDOWN_EVENT.

There are two consequences of specifying -Xrs:

 * Ctrl-Break thread dumps are not available.

 * User code is responsible for causing shutdown hooks to run, for example by
   calling System.exit() when the Java VM is to be terminated.

-Xssn

Sets the thread stack size.

-Xverify:mode

Sets the mode of the bytecode verifier. Bytecode verification ensures that class
files are properly formed and satisfy the constraints listed in section 4.10,
Verification of class Files in the The Java Virtual Machine Specification.

Do not turn off verification as this reduces the protection provided by Java and
could cause problems due to ill-formed class files.

Possible mode arguments for this option include the following:

remote

Verifies all bytecodes not loaded by the bootstrap class loader. This is the
default behavior if you do not specify the -Xverify option.

all

Enables verification of all bytecodes.

none

Disables verification of all bytecodes. Use of -Xverify:none is unsupported.

-XX:AllocationPrefetchStyle=n

Sets the style of prefetch used during allocation. default=2.

-XX:+AggressiveOpts

Enables aggressive optimization.

-XX:+|-DisableAttachMechanism

Specifies whether commands (such as jmap and jconsole) can attach to the Java
VM. By default, this feature is disabled. That is, attaching is enabled, for
example:

java -XX:+DisableAttachMechanism


-XX:+|-FlightRecorder

Toggles the use of the Java Flight Recorder (JFR) during the runtime of the
application. This is a commercial feature that requires you to also specify the
-XX:+UnlockCommercialFeatures option as follows:

java -XX:UnlockCommercialFeatures -XX:+FlightRecorder


-XX:FlightRecorderOptions=parameter=value

Sets the parameters that control the behavior of JFR. This option can be used
only when JFR is enabled (that is, the -XX:+FlightRecorder option is specified).

The following list contains all available JFR parameters:

defaultrecording=true|false

Specifies whether the recording is a continuous background recording or it runs
for a limited time. By default, this parameter is set to false (recording runs
for a limited time). To make the recording run continuously, set the parameter
to true.

disk=true|false

Specifies whether JFR should write a continuous recording to disk. By default,
this parameter is set to false (continuous recording to disk is disabled). To
enable it, set the parameter to true., and also set defaultrecording=true.

dumponexit=true|false

Specifies whether a dump file of JFR data should be generated when the JVM
terminates in a controlled manner. By default, this parameter is set to false
(dump file on exit is not generated). To enable it, set the parameter to true,
and also set defaultrecording=true.

The dump file is written to the location defined by the dumponexitpath
parameter.

dumponexitpath=path

Specifies the path and name of the dump file with JFR data that is created when
the JVM exits in a controlled manner if you set the dumponexit=true parameter.
Setting the path makes sense only if you also set defaultrecording=true.

If the specified path is a directory, the JVM assigns a file name that shows the
creation date and time. If the specified path includes a file name and if that
file already exists, the JVM creates a new file by appending the date and time
stamp to the specified file name.

globalbuffersize=size

Specifies the total amount of primary memory (in bytes) used for data retention.
Append k or K, to specify the size in KB, m or M to specify the size in MB, g or
G to specify the size in GB. By default, the size is set to 462848 bytes.

loglevel=quiet|terror|warning|info|debug|trace

Specify the amount of data written to the log file by JFR. By default, it is set
to info.

maxage=time

Specifies the maximum age (in minutes) of disk data for default recording. By
default, the maximum age is set to 15 minutes.This parameter is valid only if
you set the disk=true parameter.

maxchunksize=size

Specifies the maximum size (in bytes) of the data chunks in a recording. Append
k or K, to specify the size in KB, m or M to specify the size in MB, g or G to
specify the size in GB. By default, the maximum size of data chunks is set to 12
MB.

maxsize=size

Specifies the maximum size (in bytes) of disk data for default recording. Append
k or K, to specify the size in KB, m or M to specify the size in MB, g or G to
specify the size in GB. By default, the maximum size of disk data is not
limited.

This parameter is valid only if you set the disk=true parameter.

repository=path

Specifies the repository (a directory) for temporary disk storage. By default,
the system's temporary directory is used.

samplethreads=true|false

Specifies whether thread sampling is enabled. thread sampling occurs only if the
sampling event is enabled along with this parameter. by default, this parameter
is enabled.

settings=path

Specifies the path and name of the event settings file (of type JFC). By
default, the default.jfc file is used, which is located in
JAVA_HOME/jre/lib/jfr.

stackdepth=depth

Stack depth for stack traces by JFR. By default, the depth is set to 64 method
calls. The maximum is 2048, minimum is 1.

threadbuffersize=size

Specifies the per-thread local buffer size (in bytes). Append k or K, to specify
the size in KB, m or M to specify the size in MB, g or G to specify the size in
GB. Higher values for this parameter allow more data gathering without
contention to flush it to the global storage. It can increase application
footprint in a thread-rich environment. By default, the local buffer size is set
to 5 KB.

You can specify values for multiple parameters by separating them with a comma.
For example, to instruct JFR to write a continuous recording to disk, and set
the maximum size of data chunks to 10 MB, specify the following:

-XX:FlightRecorderOptions=defaultrecording=true,disk=true,maxchunksize=10M


-XXLargePageSizeInBytes=n

Specifies the maximum size for large pages.

-XX:MaxGCPauseMillis=n

Sets a target for the maximum GC pause time.

This is a soft goal, and the Java VM will make its best effort to achieve it.
There is no maximum value set by default.

-XX:NewSize

Sets the size of the young generation (nursery). Sames as -Xmnsize.

-XX:ParallelGCThreads=n

Sets the number of GC threads in the parallel collectors.

-XX:PredictedClassLoadCount=n

This option requires that the UnlockExperimentalVMOptions flag be set first. Use
the PredictedClassLoadCount flag if your application loads a lot of classes and
especially if class.forName() is used heavily. The recommended value is the
number of classes loaded as shown in the output from -verbose:class.

Example:

java -XX:+UnlockExperimentalVMOptions -XX:PredictedClassLoadCount=60013


-XX:+PrintCompilation

Prints verbose output from the Java HotSpot VM dynamic runtime compiler.

-XX:+PrintGCDetails -XX:+PrintGCTimeStamps

Prints garbage collection output along with time stamps.

-XX:SoftRefLRUPolicyMSPerMB=0

This flag enables aggressive processing of software references. Use this flag if
the software reference count has an impact on the Java HotSpot VM garbage
collector.

-XX:StartFlightRecording=parameter=value

Starts a JFR recording for the Java application. This option is equivalent to
the JFR.start diagnostic command that starts a recording during runtime. You can
set the following parameters when starting a JFR recording:

compress=true|false

Specifies whether to compress the JFR recording log file (of type JFR) on the
disk using the gzip file compression utility. This parameter is valid only if
the filename parameter is specified. By defaut it is set to false (recording is
not compressed). To enable compression, set the parameter to true.

defaultrecording=true|false

Specifies whether the recording is a continuous background recording or it runs
for a limited time. By default, this parameter is set to false (recording runs
for a limited time). To make the recording run continuously, set the parameter
to true.

delay=time

Specifies the delay (in milliseconds) between the Java application launch time
and the start of the recording. By default, there is no delay and this parameter
is set to 0.

duration=time

Specifies the duration (in milliseconds) of the recording. By default, the
duration is not limited.

filename=path

Specifies the path and name of the JFR recording log file.

name=identifier

Specifies the identifier for the JFR recording. By default, it is set to
Recording x.

maxage=time

Specifies the maximum age (in minutes) of disk data for default recording. By
default, the maximum age is set to 15 minutes.

maxsize=size

Specifies the maximum size (in bytes) of the recording before it is flushed from
the thread buffer to the global buffer. Append k or K, to specify the size in
KB, m or M to specify the size in MB, g or G to specify the size in GB. By
default, the maximum size is not limited.

This parameter is valid only for size-bound recordings.

settings=path

Specifies the path and name of the event settings file (of type JFC). By
default, the default.jfc file is used, which is located in
JAVA_HOME/jre/lib/jfr.

You can specify values for multiple parameters by separating them with a comma.
For example, to save the recording to test.jfr in the current working directory,
and instruct JFR to compress the log file, specify the following:

-XX:StartFlightRecording=filename=test.jfr,compress=true


-XX:TLABSize=n

Thread local allocation buffers (TLAB) are enabled by default in the Java
HotSpot VM. The Java HotSpot VM sizes TLABs based on allocation patterns. The
-XX:TLABSize option enables fine-tuning the size of TLABs.

-XX:+UnlockCommercialFeatures

Use this flag to actively unlock the use of commercial features. Commercial
features are the products Oracle Java SE Advanced or Oracle Java SE Suite, as
defined at the Java SE Products web page.

If this flag is not specified, then the default is to run the Java Virtual
Machine without the commercial features being available. After they are enabled,
it is not possible to disable their use at runtime.

-XX:+|-UseCompressedOops

Enables compressed references in 64-bit Java VMs.

This option is true by default.

-XX:+UseConcMarkSweepGC or -XX:+UseG1GC

Enables either the Concurrent Mark Sweep (CMS) or the G1 garbage collectors.

-XX:+|-UseLargePages

Enables large page support.

-XX:+UseParallelOldGC

Enables the parallel garbage collectors, which are optimized for throughput and
average response time.


NOTES

The -version:release option places no restrictions on the complexity of the
release specification. However, only a restricted subset of the possible release
specifications represent sound policy and only these are fully supported. These
policies are:

 1. Any version, represented by not using this option.

 2. Any version greater than an arbitrarily precise version-id value, for
    example:
    
    "1.6.0_10+"
    
    
    This would utilize any version greater than 1.6.0_10. This is useful for a
    case where an interface was introduced (or a bug fixed) in the release
    specified.

 3. A version greater than an arbitrarily precise version-id, bounded by the
    upper bound of that release family, for example:
    
    "1.6.0_10+&1.6*"
    

 4. An or expressions of items 2 or 3, for example:
    
     "1.6.0_10+&1.6* 1.7+"
    
    
    Similar to item 2. This is useful when a change was introduced in a release
    (1.7) but also made available in updates to earlier releases.


PERFORMANCE TUNING EXAMPLES

The following examples show how to use experimental tuning flags to optimize
either throughput or faster response time.

Example 1Tuning for Higher Throughput

java -d64 -server -XX:+AggressiveOpts -XX:+UseLargePages -Xmn10g  -Xms26g -Xmx26g 


Example 2Tuning for Lower Response Time

 java -d64 -XX:+UseG1GC -Xms26g Xmx26g -XX:MaxGCPauseMillis=500 -XX:+PrintGCTimeStamps 



EXIT STATUS

The following exit values are typically returned by the launcher, typically when
the launcher is called with the wrong arguments, serious errors, or exceptions
thrown from the Java Virtual Machine. However, a Java application may choose to
return any value using the API call System.exit(exitValue).

 * 0: Successful completion

 * >0: An error occurred


SEE ALSO

   

 * javac

 * jdb

 * javah

 * jar

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