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.\" Title: java

.\" Language: English

.\" Date: 03 March 2015

.\" SectDesc: Basic Tools

.\" Software: JDK 8

.\" Arch: generic

.\" Part Number: E38207-04

.\" Doc ID: JSSON

.\"

.if n .pl 99999

.TH "java" "1" "03 March 2015" "JDK 8" "Basic Tools"

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.\" * MAIN CONTENT STARTS HERE *

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

.SH "NAME"

java \- Launches a Java application\&.

.SH "SYNOPSIS"

.sp

.if n \{\

.RS 4

.\}

.nf

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

.fi

.if n \{\

.RE

.\}

.sp

.if n \{\

.RS 4

.\}

.nf

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

.fi

.if n \{\

.RE

.\}

.PP

\fIoptions\fR

.RS 4

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

.RE

.PP

\fIclassname\fR

.RS 4

The name of the class to be launched\&.

.RE

.PP

\fIfilename\fR

.RS 4

The name of the Java Archive (JAR) file to be called\&. Used only with the

\fB\-jar\fR

option\&.

.RE

.PP

\fIargs\fR

.RS 4

The arguments passed to the

\fBmain()\fR

method separated by spaces\&.

.RE

.SH "DESCRIPTION"

.PP

The

\fBjava\fR

command starts a Java application\&. It does this by starting the Java Runtime Environment (JRE), loading the specified class, and calling that class\*(Aqs

\fBmain()\fR

method\&. The method must be declared

\fIpublic\fR

and

\fIstatic\fR, it must not return any value, and it must accept a

\fBString\fR

array as a parameter\&. The method declaration has the following form:

.sp

.if n \{\

.RS 4

.\}

.nf

\fBpublic static void main(String[] args)\fR

.fi

.if n \{\

.RE

.\}

.PP

The

\fBjava\fR

command can be used to launch a JavaFX application by loading a class that either has a

\fBmain()\fR

method or that extends

\fBjavafx\&.application\&.Application\fR\&. In the latter case, the launcher constructs an instance of the

\fBApplication\fR

class, calls its

\fBinit()\fR

method, and then calls the

\fBstart(javafx\&.stage\&.Stage)\fR

method\&.

.PP

By default, the first argument that is not an option of the

\fBjava\fR

command is the fully qualified name of the class to be called\&. If the

\fB\-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

\fBMain\-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

\fBmain()\fR

method\&.

.SH "OPTIONS"

.PP

The

\fBjava\fR

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

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Standard Options

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Non\-Standard Options

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Advanced Runtime Options

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Advanced JIT Compiler Options

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Advanced Serviceability Options

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

Advanced Garbage Collection Options

.RE

.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

\fB\-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

\fB\-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

\fB\-XX\fR

options are enabled using the plus sign (\fB\-XX:+\fR\fIOptionName\fR) and disabled using the minus sign (\fB\-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

\fBk\fR

or

\fBK\fR

for kilobytes (KB),

\fBm\fR

or

\fBM\fR

for megabytes (MB),

\fBg\fR

or

\fBG\fR

for gigabytes (GB)\&. For example, to set the size to 8 GB, you can specify either

\fB8g\fR,

\fB8192m\fR,

\fB8388608k\fR, or

\fB8589934592\fR

as the argument\&. If you are expected to specify the percentage, use a number from 0 to 1 (for example, specify

\fB0\&.25\fR

for 25%)\&.

.SS "Standard Options"

.PP

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

.PP

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

.RS 4

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

.sp

If the option

\fB\-agentlib:foo\fR

is specified, then the JVM attempts to load the library named

\fBlibfoo\&.so\fR

in the location specified by the

\fBLD_LIBRARY_PATH\fR

system variable (on OS X this variable is

\fBDYLD_LIBRARY_PATH\fR)\&.

.sp

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

.if n \{\

.RS 4

.\}

.nf

\fB\-agentlib:hprof=cpu=samples,interval=20,depth=3\fR

.fi

.if n \{\

.RE

.\}

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

.if n \{\

.RS 4

.\}

.nf

\fB\-agentlib:jdwp=transport=dt_socket,server=y,address=8000\fR

.fi

.if n \{\

.RE

.\}

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

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

The

\fBjava\&.lang\&.instrument\fR

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

.RE

.sp

.RS 4

.ie n \{\

\h'-04'\(bu\h'+03'\c

.\}

.el \{\

.sp -1

.IP \(bu 2.3

.\}

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

.RE

.RE

.PP

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

.RS 4

Loads the native agent library specified by the absolute path name\&. This option is equivalent to

\fB\-agentlib\fR

but uses the full path and file name of the library\&.

.RE

.PP

\-client

.RS 4

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\&.

.sp

For default JVM selection, see Server\-Class Machine Detection at

http://docs\&.oracle\&.com/javase/8/docs/technotes/guides/vm/server\-class\&.html

.RE

.PP

\-D\fIproperty\fR=\fIvalue\fR

.RS 4

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

\fB\-Dfoo="foo bar"\fR)\&.

.RE

.PP

\-d32

.RS 4

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\&.

.RE

.PP

\-d64

.RS 4

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\&.

.sp

Currently only the Java HotSpot Server VM supports 64\-bit operation, and the

\fB\-server\fR

option is implicit with the use of

\fB\-d64\fR\&. The

\fB\-client\fR

option is ignored with the use of

\fB\-d64\fR\&. This is subject to change in a future release\&.

.RE

.PP

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

.br

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

.RS 4

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

.sp

With no arguments,

\fB\-disableassertions\fR

(\fB\-da\fR) disables assertions in all packages and classes\&. With the

\fIpackagename\fR

argument ending in

\fB\&.\&.\&.\fR, the switch disables assertions in the specified package and any subpackages\&. If the argument is simply

\fB\&.\&.\&.\fR, then the switch disables assertions in the unnamed package in the current working directory\&. With the

\fIclassname\fR

argument, the switch disables assertions in the specified class\&.

.sp

The

\fB\-disableassertions\fR

(\fB\-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

\fB\-disablesystemassertions\fR

option enables you to disable assertions in all system classes\&.

.sp

To explicitly enable assertions in specific packages or classes, use the

\fB\-enableassertions\fR

(\fB\-ea\fR) option\&. Both options can be used at the same time\&. For example, to run the

\fBMyClass\fR

application with assertions enabled in package

\fBcom\&.wombat\&.fruitbat\fR

(and any subpackages) but disabled in class

\fBcom\&.wombat\&.fruitbat\&.Brickbat\fR, use the following command:

.sp

.if n \{\

.RS 4

.\}

.nf

\fBjava \-ea:com\&.wombat\&.fruitbat\&.\&.\&. \-da:com\&.wombat\&.fruitbat\&.Brickbat MyClass\fR

.fi

.if n \{\

.RE

.\}

.RE

.PP

\-disablesystemassertions

.br

\-dsa

.RS 4

Disables assertions in all system classes\&.

.RE

.PP

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

.br

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

.RS 4

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

.sp

With no arguments,

\fB\-enableassertions\fR

(\fB\-ea\fR) enables assertions in all packages and classes\&. With the

\fIpackagename\fR

argument ending in

\fB\&.\&.\&.\fR, the switch enables assertions in the specified package and any subpackages\&. If the argument is simply

\fB\&.\&.\&.\fR, then the switch enables assertions in the unnamed package in the current working directory\&. With the

\fIclassname\fR

argument, the switch enables assertions in the specified class\&.

.sp

The

\fB\-enableassertions\fR

(\fB\-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

\fB\-enablesystemassertions\fR

option provides a separate switch to enable assertions in all system classes\&.

.sp

To explicitly disable assertions in specific packages or classes, use the

\fB\-disableassertions\fR

(\fB\-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

\fBMyClass\fR

application with assertions enabled only in package

\fBcom\&.wombat\&.fruitbat\fR

(and any subpackages) but disabled in class

\fBcom\&.wombat\&.fruitbat\&.Brickbat\fR, use the following command:

.sp

.if n \{\

.RS 4

.\}

.nf

\fBjava \-ea:com\&.wombat\&.fruitbat\&.\&.\&. \-da:com\&.wombat\&.fruitbat\&.Brickbat MyClass\fR

.fi

.if n \{\

.RE

.\}

.RE

.PP

\-enablesystemassertions

.br

\-esa

.RS 4

Enables assertions in all system classes\&.

.RE

.PP

\-help

.br

\-?

.RS 4

Displays usage information for the

\fBjava\fR

command without actually running the JVM\&.

.RE

.PP

\-jar \fIfilename\fR

.RS 4

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

\fBMain\-Class:\fR\fIclassname\fR

that defines the class with the

\fBpublic static void main(String[] args)\fR

method that serves as your application\*(Aqs starting point\&.

.sp

When you use the

\fB\-jar\fR

option, the specified JAR file is the source of all user classes, and other class path settings are ignored\&.

.sp

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