'\" t

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.\"     Arch: generic

.\"     Software: JDK 8

.\"     Date: 21 November 2013

.\"     SectDesc: Basic Tools

.\"     Title: java.1

.\"

.if n .pl 99999

.TH java 1 "21 November 2013" "JDK 8" "Basic Tools"

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.\" * MAIN CONTENT STARTS HERE *

.\" -----------------------------------------------------------------

.SH NAME    

java \- Launches a Java application\&.

.SH SYNOPSIS    

.sp     

.nf     

\fBjava\fR [\fIoptions\fR] \fIclassname\fR [\fIargs\fR]

.fi     

.nf     

\fBjava\fR [\fIoptions\fR] \fB\-jar\fR \fIfilename\fR [\fIargs\fR]

.fi     

.sp     

.TP     

\fIoptions\fR

Command-line options separated by spaces\&. See Options\&.

.TP     

\fIclassname\fR

The name of the class to be launched\&.

.TP     

\fIfilename\fR

The name of the Java Archive (JAR) file to be called\&. Used only with the \f3-jar\fR option\&.

.TP     

\fIargs\fR

The arguments passed to the \f3main()\fR method separated by spaces\&.

.SH DESCRIPTION    

The \f3java\fR command starts a Java application\&. It does this by starting the Java Runtime Environment (JRE), loading the specified class, and calling that class\&'s \f3main()\fR method\&. The method must be declared \fIpublic\fR and \fIstatic\fR, it must not return any value, and it must accept a \f3String\fR array as a parameter\&. The method declaration has the following form:

.sp     

.nf     

\f3public static void main(String[] args)\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

The \f3java\fR command can be used to launch a JavaFX application by loading a class that either has a \f3main()\fR method or that extends \f3javafx\&.application\&.Application\fR\&. In the latter case, the launcher constructs an instance of the \f3Application\fR class, calls its \f3init()\fR method, and then calls the \f3start(javafx\&.stage\&.Stage)\fR method\&.

.PP

By default, the first argument that is not an option of the \f3java\fR command is the fully qualified name of the class to be called\&. If the \f3-jar\fR option is specified, its argument is the name of the JAR file containing class and resource files for the application\&. The startup class must be indicated by the \f3Main-Class\fR manifest header in its source code\&.

.PP

The JRE searches for the startup class (and other classes used by the application) in three sets of locations: the bootstrap class path, the installed extensions, and the user\(cqs class path\&.

.PP

Arguments after the class file name or the JAR file name are passed to the \f3main()\fR method\&.

.SH OPTIONS    

The \f3java\fR command supports a wide range of options that can be divided into the following categories:

.TP 0.2i    

\(bu

Standard Options

.TP 0.2i    

\(bu

Non-Standard Options

.TP 0.2i    

\(bu

Advanced Runtime Options

.TP 0.2i    

\(bu

Advanced JIT Compiler Options

.TP 0.2i    

\(bu

Advanced Serviceability Options

.TP 0.2i    

\(bu

Advanced Garbage Collection Options

.PP

Standard options are guaranteed to be supported by all implementations of the Java Virtual Machine (JVM)\&. They are used for common actions, such as checking the version of the JRE, setting the class path, enabling verbose output, and so on\&.

.PP

Non-standard options are general purpose options that are specific to the Java HotSpot Virtual Machine, so they are not guaranteed to be supported by all JVM implementations, and are subject to change\&. These options start with \f3-X\fR\&.

.PP

Advanced options are not recommended for casual use\&. These are developer options used for tuning specific areas of the Java HotSpot Virtual Machine operation that often have specific system requirements and may require privileged access to system configuration parameters\&. They are also not guaranteed to be supported by all JVM implementations, and are subject to change\&. Advanced options start with \f3-XX\fR\&.

.PP

To keep track of the options that were deprecated or removed in the latest release, there is a section named Deprecated and Removed Options at the end of the document\&.

.PP

Boolean options are used to either enable a feature that is disabled by default or disable a feature that is enabled by default\&. Such options do not require a parameter\&. Boolean \f3-XX\fR options are enabled using the plus sign (\f3-XX:+\fR\fIOptionName\fR) and disabled using the minus sign (\f3-XX:-\fR\fIOptionName\fR)\&.

.PP

For options that require an argument, the argument may be separated from the option name by a space, a colon (:), or an equal sign (=), or the argument may directly follow the option (the exact syntax differs for each option)\&. If you are expected to specify the size in bytes, you can use no suffix, or use the suffix \f3k\fR or \f3K\fR for kilobytes (KB), \f3m\fR or \f3M\fR for megabytes (MB), \f3g\fR or \f3G\fR for gigabytes (GB)\&. For example, to set the size to 8 GB, you can specify either \f38g\fR, \f38192m\fR, \f38388608k\fR, or \f38589934592\fR as the argument\&. If you are expected to specify the percentage, use a number from 0 to 1 (for example, specify \f30\&.25\fR for 25%)\&.

.SS STANDARD\ OPTIONS    

These are the most commonly used options that are supported by all implementations of the JVM\&.

.TP

-agentlib:\fIlibname\fR[=\fIoptions\fR]

.br

Loads the specified native agent library\&. After the library name, a comma-separated list of options specific to the library can be used\&.

If the option \f3-agentlib:foo\fR is specified, then the JVM attempts to load the library named \f3libfoo\&.so\fR in the location specified by the \f3LD_LIBRARY_PATH\fR system variable (on OS X this variable is \f3DYLD_LIBRARY_PATH\fR)\&.

The following example shows how to load the heap profiling tool (HPROF) library and get sample CPU information every 20 ms, with a stack depth of 3:

.sp     

.nf     

\f3\-agentlib:hprof=cpu=samples,interval=20,depth=3\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

The following example shows how to load the Java Debug Wire Protocol (JDWP) library and listen for the socket connection on port 8000, suspending the JVM before the main class loads:

.sp     

.nf     

\f3\-agentlib:jdwp=transport=dt_socket,server=y,address=8000\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

For more information about the native agent libraries, refer to the following:

.RS     

.TP 0.2i    

\(bu

The \f3java\&.lang\&.instrument\fR package description at http://docs\&.oracle\&.com/javase/8/docs/api/java/lang/instrument/package-summary\&.html

.TP 0.2i    

\(bu

Agent Command Line Options in the JVM Tools Interface guide at http://docs\&.oracle\&.com/javase/8/docs/platform/jvmti/jvmti\&.html#starting

.RE     

.TP

-agentpath:\fIpathname\fR[=\fIoptions\fR]

.br

Loads the native agent library specified by the absolute path name\&. This option is equivalent to \f3-agentlib\fR but uses the full path and file name of the library\&.

.TP

-client

.br

Selects the Java HotSpot Client VM\&. The 64-bit version of the Java SE Development Kit (JDK) currently ignores this option and instead uses the Server JVM\&.

For default JVM selection, see Server-Class Machine Detection at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/server-class\&.html

.TP

-D\fIproperty\fR=\fIvalue\fR

.br

Sets a system property value\&. The \fIproperty\fR variable is a string with no spaces that represents the name of the property\&. The \fIvalue\fR variable is a string that represents the value of the property\&. If \fIvalue\fR is a string with spaces, then enclose it in quotation marks (for example \f3-Dfoo="foo bar"\fR)\&.

.TP

-d32

.br

Runs the application in a 32-bit environment\&. If a 32-bit environment is not installed or is not supported, then an error will be reported\&. By default, the application is run in a 32-bit environment unless a 64-bit system is used\&.

.TP

-d64

.br

Runs the application in a 64-bit environment\&. If a 64-bit environment is not installed or is not supported, then an error will be reported\&. By default, the application is run in a 32-bit environment unless a 64-bit system is used\&.

Currently only the Java HotSpot Server VM supports 64-bit operation, and the \f3-server\fR option is implicit with the use of \f3-d64\fR\&. The \f3-client\fR option is ignored with the use of \f3-d64\fR\&. This is subject to change in a future release\&.

.TP

.nf

-disableassertions[:[\fIpackagename\fR]\&.\&.\&.|:\fIclassname\fR], -da[:[\fIpackagename\fR]\&.\&.\&.|:\fIclassname\fR]

.br

.fi

Disables assertions\&. By default, assertions are disabled in all packages and classes\&.

With no arguments, \f3-disableassertions\fR (\f3-da\fR) disables assertions in all packages and classes\&. With the \fIpackagename\fR argument ending in \f3\&.\&.\&.\fR, the switch disables assertions in the specified package and any subpackages\&. If the argument is simply \f3\&.\&.\&.\fR, then the switch disables assertions in the unnamed package in the current working directory\&. With the \fIclassname\fR argument\f3\fR, the switch disables assertions in the specified class\&.

The \f3-disableassertions\fR (\f3-da\fR) option applies to all class loaders and to system classes (which do not have a class loader)\&. There is one exception to this rule: if the option is provided with no arguments, then it does not apply to system classes\&. This makes it easy to disable assertions in all classes except for system classes\&. The \f3-disablesystemassertions\fR option enables you to disable assertions in all system classes\&.

To explicitly enable assertions in specific packages or classes, use the \f3-enableassertions\fR (\f3-ea\fR) option\&. Both options can be used at the same time\&. For example, to run the \f3MyClass\fR application with assertions enabled in package \f3com\&.wombat\&.fruitbat\fR (and any subpackages) but disabled in class \f3com\&.wombat\&.fruitbat\&.Brickbat\fR, use the following command:

.sp     

.nf     

\f3java \-ea:com\&.wombat\&.fruitbat\&.\&.\&. \-da:com\&.wombat\&.fruitbat\&.Brickbat MyClass\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

.TP

-disablesystemassertions, -dsa

.br

Disables assertions in all system classes\&.

.TP

.nf

-enableassertions[:[\fIpackagename\fR]\&.\&.\&.|:\fIclassname\fR], -ea[:[\fIpackagename\fR]\&.\&.\&.|:\fIclassname\fR]

.br

.fi

Enables assertions\&. By default, assertions are disabled in all packages and classes\&.

With no arguments, \f3-enableassertions\fR (\f3-ea\fR) enables assertions in all packages and classes\&. With the \fIpackagename\fR argument ending in \f3\&.\&.\&.\fR, the switch enables assertions in the specified package and any subpackages\&. If the argument is simply \f3\&.\&.\&.\fR, then the switch enables assertions in the unnamed package in the current working directory\&. With the \fIclassname\fR argument\f3\fR, the switch enables assertions in the specified class\&.

The \f3-enableassertions\fR (\f3-ea\fR) option applies to all class loaders and to system classes (which do not have a class loader)\&. There is one exception to this rule: if the option is provided with no arguments, then it does not apply to system classes\&. This makes it easy to enable assertions in all classes except for system classes\&. The \f3-enablesystemassertions\fR option provides a separate switch to enable assertions in all system classes\&.

To explicitly disable assertions in specific packages or classes, use the \f3-disableassertions\fR (\f3-da\fR) option\&. If a single command contains multiple instances of these switches, then they are processed in order before loading any classes\&. For example, to run the \f3MyClass\fR application with assertions enabled only in package \f3com\&.wombat\&.fruitbat\fR (and any subpackages) but disabled in class \f3com\&.wombat\&.fruitbat\&.Brickbat\fR, use the following command:

.sp     

.nf     

\f3java \-ea:com\&.wombat\&.fruitbat\&.\&.\&. \-da:com\&.wombat\&.fruitbat\&.Brickbat MyClass\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

.TP

-enablesystemassertions, -esa

.br

Enables assertions in all system classes\&.

.TP

-help, -?

.br

Displays usage information for the \f3java\fR command without actually running the JVM\&.

.TP

-jar \fIfilename\fR

.br

Executes a program encapsulated in a JAR file\&. The \fIfilename\fR argument is the name of a JAR file with a manifest that contains a line in the form \f3Main-Class:\fR\fIclassname\fR that defines the class with the \f3public static void main(String[] args)\fR method that serves as your application\&'s starting point\&.

When you use the \f3-jar\fR option, the specified JAR file is the source of all user classes, and other class path settings are ignored\&.

For more information about JAR files, see the following resources:

.RS     

.TP 0.2i    

\(bu

jar(1)

.TP 0.2i    

\(bu

The Java Archive (JAR) Files guide at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/jar/index\&.html

.TP 0.2i    

\(bu

Lesson: Packaging Programs in JAR Files at http://docs\&.oracle\&.com/javase/tutorial/deployment/jar/index\&.html

.RE     

.TP

-javaagent:\fIjarpath\fR[=\fIoptions\fR]

.br

Loads the specified Java programming language agent\&. For more information about instrumenting Java applications, see the \f3java\&.lang\&.instrument\fR package description in the Java API documentation at http://docs\&.oracle\&.com/javase/8/docs/api/java/lang/instrument/package-summary\&.html

.TP

-jre-restrict-search

.br

Includes user-private JREs in the version search\&.

.TP

-no-jre-restrict-search

.br

Excludes user-private JREs from the version search\&.

.TP

-server

.br

Selects the Java HotSpot Server VM\&. The 64-bit version of the JDK supports only the Server VM, so in that case the option is implicit\&.

For default JVM selection, see Server-Class Machine Detection at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/server-class\&.html

.TP

-showversion

.br

Displays version information and continues execution of the application\&. This option is equivalent to the \f3-version\fR option except that the latter instructs the JVM to exit after displaying version information\&.

.TP

-splash:\fIimgname\fR

.br

Shows the splash screen with the image specified by \fIimgname\fR\&. For example, to show the \f3splash\&.gif\fR file from the \f3images\fR directory when starting your application, use the following option:

.sp     

.nf     

\f3\-splash:images/splash\&.gif\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

.TP

-verbose:class

.br

Displays information about each loaded class\&.

.TP

-verbose:gc

.br

Displays information about each garbage collection (GC) event\&.

.TP

-verbose:jni

.br

Displays information about the use of native methods and other Java Native Interface (JNI) activity\&.

.TP

-version

.br

Displays version information and then exits\&. This option is equivalent to the \f3-showversion\fR option except that the latter does not instruct the JVM to exit after displaying version information\&.

.TP

-version:\fIrelease\fR

.br

Specifies the release version to be used for running the application\&. If the version of the \f3java\fR command called does not meet this specification and an appropriate implementation is found on the system, then the appropriate implementation will be used\&.

The \fIrelease\fR argument specifies either the exact version string, or a list of version strings and ranges separated by spaces\&. A \fIversion string\fR is the developer designation of the version number in the following form: \f31\&.\fR\fIx\fR\f3\&.0_\fR\fIu\fR (where \fIx\fR is the major version number, and \fIu\fR is the update version number)\&. A \fIversion range\fR is made up of a version string followed by a plus sign (\f3+\fR) to designate this version or later, or a part of a version string followed by an asterisk (\f3*\fR) to designate any version string with a matching prefix\&. Version strings and ranges can be combined using a space for a logical \fIOR\fR combination, or an ampersand (\f3&\fR) for a logical \fIAND\fR combination of two version strings/ranges\&. For example, if running the class or JAR file requires either JRE 6u13 (1\&.6\&.0_13), or any JRE 6 starting from 6u10 (1\&.6\&.0_10), specify the following:

.sp     

.nf     

\f3\-version:"1\&.6\&.0_13 1\&.6* & 1\&.6\&.0_10+"\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

Quotation marks are necessary only if there are spaces in the \fIrelease\fR parameter\&.

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

.SS NON-STANDARD\ OPTIONS    

These options are general purpose options that are specific to the Java HotSpot Virtual Machine\&.

.TP

-X

.br

Displays help for all available \f3-X\fR options\&.

.TP

-Xbatch

.br

Disables background compilation\&. By default, the JVM compiles the method as a background task, running the method in interpreter mode until the background compilation is finished\&. The \f3-Xbatch\fR flag disables background compilation so that compilation of all methods proceeds as a foreground task until completed\&.

This option is equivalent to \f3-XX:-BackgroundCompilation\fR\&.

.TP

-Xbootclasspath:\fIpath\fR

.br

Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to search for boot class files\&. These are used in place of the boot class files included in the JDK\&.

\fI\fRDo not deploy applications that use this option to override a class in \f3rt\&.jar\fR, because this violates the JRE binary code license\&.

.TP

-Xbootclasspath/a:\fIpath\fR

.br

Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to append to the end of the default bootstrap class path\&.

Do not deploy applications that use this option to override a class in \f3rt\&.jar\fR, because this violates the JRE binary code license\&.

.TP

-Xbootclasspath/p:\fIpath\fR

.br

Specifies a list of directories, JAR files, and ZIP archives separated by colons (:) to prepend to the front of the default bootstrap class path\&.

Do not deploy applications that use this option to override a class in \f3rt\&.jar\fR, because this violates the JRE binary code license\&.

.TP

-Xboundthreads

.br

Binds user-level threads to kernel threads\&.

.TP

-Xcheck:jni

Performs additional checks for Java Native Interface (JNI) functions\&. Specifically, it 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 JVM will terminate with an irrecoverable error in such cases\&. Expect a performance degradation when this option is used\&.

.TP

-Xcomp

.br

Disables interpretation of Java code and compile methods on first invocation\&. By default, the JIT compiler performs 10,000 interpreted method invocations to gather information for efficient compilation\&. To increase compilation performance at the expense of efficiency, use the \f3-Xcomp\fR flag to disable interpreted method invocations\&.

You can also change the number of interpreted method invocations before compilation using the \f3-XX:CompileThreshold\fR option\&.

.TP

-Xdebug

.br

Does nothing\&. Provided for backward compatibility\&.

.TP

-Xdiag

.br

Shows additional diagnostic messages\&.

.TP

-Xfuture

.br

Enables strict class-file format checks that enforce close 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\&.

.TP

-Xincgc

.br

Enables incremental GC\&.

.TP

-Xint

.br

Runs the application in interpreted-only mode\&. Compilation to native code is disabled, and all bytecode is executed by the interpreter\&. The performance benefits offered by the just in time (JIT) compiler are not present in this mode\&.

.TP

-Xinternalversion

Displays more detailed JVM version information than the \f3-version\fR option, and then exits\&.

.TP

-Xloggc:\fIfilename\fR

Sets the file to which verbose GC events information should be redirected for logging\&. The information written to this file is similar to the output of \f3-verbose:gc\fR with the time elapsed since the first GC event preceding each logged event\&. The \f3-Xloggc\fR option overrides \f3-verbose:gc\fR if both are given with the same \f3java\fR command\&.

Example:

.sp     

.nf     

\f3\-Xloggc:garbage\-collection\&.log\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

.TP

-Xmaxjitcodesize=\fIsize\fR

Specifies the maximum code cache size (in bytes) for JIT-compiled code\&. Append the letter \f3k\fR or \f3K\fR to indicate kilobytes, \f3m\fR or \f3M\fR to indicate megabytes, \f3g\fR or \f3G\fR to indicate gigabytes\&. By default, the value is set to 48 MB:

.sp     

.nf     

\f3\-Xmaxjitcodesize=48m\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

This option is equivalent to \f3-XX:ReservedCodeCacheSize\fR\&.

.TP

-Xmixed

.br

Executes all bytecode by the interpreter except for hot methods, which are compiled to native code\&.

.TP

-Xmn\fIsize\fR

Sets the initial and maximum size (in bytes) of the heap for the young generation (nursery)\&. Append the letter \f3k\fR or \f3K\fR to indicate kilobytes, \f3m\fR or \f3M\fR to indicate megabytes, \f3g\fR or \f3G\fR to indicate gigabytes\&.

The young generation region of the heap is used for new objects\&. GC is performed in this region more often than in other regions\&. If the size for the young generation is too small, then a lot of minor garbage collections will be performed\&. If the size is too large, then only full garbage collections will be performed, which can take a long time to complete\&. Oracle recommends that you keep the size for the young generation between a half and a quarter of the overall heap size\&.

The following examples show how to set the initial and maximum size of young generation to 256 MB using various units:

.sp     

.nf     

\f3\-Xmn256m\fP

.fi     

.nf     

\f3\-Xmn262144k\fP

.fi     

.nf     

\f3\-Xmn268435456\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

Instead of the \f3-Xmn\fR option to set both the initial and maximum size of the heap for the young generation, you can use \f3-XX:NewSize\fR to set the initial size and \f3-XX:MaxNewSize\fR to set the maximum size\&.

.TP

-Xms\fIsize\fR

Sets the initial size (in bytes) of the heap\&. This value must be a multiple of 1024 and greater than 1 MB\&. Append the letter \f3k\fR or \f3K\fR to indicate kilobytes, \f3m\fR or \f3M\fR to indicate megabytes, \f3g\fR or \f3G\fR to indicate gigabytes\&.

The following examples show how to set the size of allocated memory to 6 MB using various units:

.sp     

.nf     

\f3\-Xms6291456\fP

.fi     

.nf     

\f3\-Xms6144k\fP

.fi     

.nf     

\f3\-Xms6m\fP

.fi     

.nf     

\f3\fP

.fi     

.sp     

If you do not set this option, then the initial size will be set as the sum of the sizes allocated for the old generation and the young generation\&. The initial size of the heap for the young generation can be set using the \f3-Xmn\fR option or the \f3-XX:NewSize\fR option\&.

.TP

-Xmx\fIsize\fR

Specifies the maximum size (in bytes) of the memory allocation pool in bytes\&. This value must be a multiple of 1024 and greater than 2 MB\&. Append the letter \f3k\fR or \f3K\fR to indicate kilobytes, \f3m\fR or \f3M\fR to indicate megabytes, \f3g\fR or \f3G\fR to indicate gigabytes\&. The default value is chosen at runtime based on system configuration\&. For server deployments, \f3-Xms\fR and \f3-Xmx\fR are often set to the same value\&. For more information, see Garbage Collector Ergonomics at http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/gc-ergonomics\&.html

The following examples show how to set the maximum allowed size of allocated memory to 80 MB using various units:

.sp     

.nf     

\f3\-Xmx83886080\fP

.fi     

.nf