java(1)java(1)Name
java - the Java application launcher
SYNOPSIS
java [ options ] class [ argument ... ]
java [ options ] -jar file.jar [ argument ... ]
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.
argument
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 applica‐
tion, 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.
OPTIONS
The launcher has a set of standard options that are supported in the
current runtime environment.
In addition, the current implementations of the virtual machines sup‐
port a set of nonstandard 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 cur‐
rently ignores this option and instead uses the Java Hotspot
Server VM.
For default Java VM selection, see Server-Class Machine Detection
at http://docs.oracle.com/javase/7/docs/tech‐
notes/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 Server-Class Machine Detec‐
tion at http://docs.oracle.com/javase/7/docs/tech‐
notes/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.ora‐
cle.com/javase/7/docs/platform/jvmti/jvmti.html#starting
-agentpath:pathname[=options]
Loads a native agent library by full pathname. See JVMTI Com‐
mand-Line Options at http://docs.oracle.com/javase/7/docs/plat‐
form/jvmti/jvmti.html#starting
-classpath classpath, -cp classpath
Specifies a list of directories, JAR files, and ZIP archives to
search for class files. Separate class path entries with 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, 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 invoca‐
tions.
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.
-d32
Run the application in a 32-bit environment. If a 32-bit environ‐
ment is not installed or is not supported, an error will be
reported. By default, the application is run in a 32-bit environ‐
ment unless a 64-bit only system is used.
-d64
Run the application in a 64-bit environment. If a 64-bit environ‐
ment is not installed or is not supported, an error will be
reported. By default, the application is run in a 32-bit environ‐
ment unless a 64-bit only system is used.
Currently only the Java HotSpot Server VM supports 64-bit opera‐
tion, and the -server option is implicit with the use of -d64.
The -client option is ignored with the use of -d64. This is sub‐
ject to change in a future release.
-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.wom‐
bat.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 load‐
ers 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 -dis‐
ablesystemassertions 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 subpack‐
ages), 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 -enablesys‐
temassertions option provides a separate switch to enable asser‐
tions in all system classes.
-enablesystemassertions, -esa
Enable assertions in all system classes (sets the default asser‐
tion 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 identi‐
fies 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.
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. See JAR File Overview at http://docs.ora‐
cle.com/javase/7/docs/technotes/guides/jar/jarGuide.html
-javaagent:jarpath[=options]
Loads a Java programming language agent. For more information
about instrumenting Java applications, see the java.lang.instru‐
ment package description in the Java API documentation at
http://docs.oracle.com/javase/7/docs/api/java/lang/instru‐
ment/package-summary.html @
http://docs.oracle.com/javase/7/docs/api/java/lang/instru‐
ment/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 continues.
-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 exits. 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 specifica‐
tion 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 ver‐
sions 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 ver‐
sion-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 ver‐
sion-id prefix and that is not less than 1.6.0_10. The exact syn‐
tax 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.
Non-Standard 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 Client VM adap‐
tive 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 inter‐
preter 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 colon-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 colon-separated path of directories, JAR files, and
ZIP archives to append to the default bootstrap class path.
-Xbootclasspath/p:path
Specifies a colon-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 Environ‐
ment binary code license.
-Xcheck:jni
Performs additional checks for Java Native Interface (JNI) func‐
tions. 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 encoun‐
tered indicates a problem in the native code, and the Java Vir‐
tual 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 compati‐
bility, the default format checks performed by the Java virtual
machine are no stricter than the checks performed by 1.1.x ver‐
sions 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 applica‐
tion launcher.
-Xnoclassgc
Disables class garbage collection. Use of this option preven mem‐
ory 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 exe‐
cution. 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 con‐
tinue 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/tech‐
notes/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.ora‐
cle.com/javase/7/docs/technotes/guides/vm/gc-ergonomics.html
Examples:
-Xmx83886080
-Xmx81920k
-Xmx80m
On Solaris 7 and Solaris 8 SPARC platforms, the upper limit for
this value is approximately 4000 m minus overhead amounts. On
Solaris 2.6 and x86 platforms, the upper limit is approximately
2000 m minus overhead amounts. On Linux platforms, the upper
limit is approximately 2000 m minus overhead amounts.
-Xprof
Profiles the running program, and sends profiling data to stan‐
dard output. This option is provided as a utility that is useful
in program development and is not intended to be used in produc‐
tion 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 catches signals to implement shutdown hooks for unex‐
pected Java VM termination. The Java VM uses SIGHUP, SIGINT, and
SIGTERM to initiate the running of shutdown hooks.
The JVM uses a similar mechanism to implement the feature of
dumping thread stacks for debugging purposes. The JVM uses
SIGQUIT to perform thread dumps.
Applications embedding the Java VM frequently need to trap sig‐
nals such as SIGINT or SIGTERM, which can lead to interference
with the Java VM signal handlers. The -Xrs command-line option is
available to address this issue. When -Xrs is used on the Java
VM, the signal masks for SIGINT, SIGTERM, SIGHUP, and SIGQUIT are
not changed by the Java VM, and signal handlers for these signals
are not installed.
There are two consequences of specifying -Xrs:
o SIGQUIT thread dumps are not available.
o User code is responsible for causing shutdown hooks to run, for
example by calling System.exit() when the Java VM is to be ter‐
minated.
-Xssn
Sets the thread stack size.
-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
-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 -Xmn‐
size.
-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 applica‐
tion 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: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:+UseAltSigs
The Java VM uses SIGUSR1 and SIGUSR2 by default, which can some‐
times conflict with applications that signal-chain SIGUSR1 and
SIGUSR2. The -XX:+UseAltSigs option causes the Java VM to use
signals other than SIGUSR1 and SIGUSR2 as the default.
-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.
Large pages are enabled by default on Solaris.
-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 1, Tuning for Higher Throughput
java -d64 -server -XX:+AggressiveOpts -XX:+UseLargePages -Xmn10g-Xms26g -Xmx26g
Example 2, Tuning 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, typi‐
cally 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 Sys‐
tem.exit(exitValue).
o 0: Successful completion
o >0: An error occurred
SEE ALSO
o javac(1)
o jdb(1)
o javah(1)
o jar(1)
18 Jul 2013 java(1)
