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java(1) - phpMan
java(1) General Commands Manual 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 envi‐
ronment, 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 func‐
tion.
OPTIONS
The launcher has a set of standard options that are supported in the current runtime envi‐
ronment.
In addition, the current implementations of the virtual machines support a set of nonstan‐
dard 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 Server-Class Machine Detection 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 Server-Class Machine Detection 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/plat‐
form/jvmti/jvmti.html#starting
-agentpath:pathname[=options]
Loads a native agent library by full pathname. See JVMTI Command-Line Options at
http://docs.oracle.com/javase/7/docs/platform/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 invocations.
For example, if directory mydir contains a.jar and b.JAR, then the class path ele‐
ment 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 Sys‐
tem.getenv("CLASSPATH").
-Dproperty=value
Sets a system property value.
-d32
Run the application in a 32-bit environment. If a 32-bit environment is not
installed or is not supported, an error will be reported. By default, the applica‐
tion is run in a 32-bit environment unless a 64-bit only system is used.
-d64
Run the application in a 64-bit environment. If a 64-bit environment is not
installed or is not supported, an error will be reported. By default, the applica‐
tion is run in a 32-bit environment unless a 64-bit only system is used.
Currently only the Java HotSpot Server VM supports 64-bit operation, and the -server
option is implicit with the use of -d64. The -client option is ignored with the use
of -d64. This is subject 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.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 -disablesystemasser‐
tions 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 sub‐
packages. 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 -enablesystemasser‐
tions 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 sys‐
tem 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.
JAR files that can be run with the java -jar option can have their execute permis‐
sions set so they can be run without using java -jar. See JAR File Overview at
http://docs.oracle.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.instrument package description in the Java API
documentation at
http://docs.oracle.com/javase/7/docs/api/java/lang/instrument/package-summary.html @
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 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 specification and an appropriate implementation is found on the sys‐
tem, then the appropriate implementation will be used.
The release option specifies an exact version and a list of versions called a ver‐
sion string. A version string is an ordered list of version ranges separated by spa‐
ces. 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.
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 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 compi‐
lation is finished. The -Xbatch flag disables background compilation so that compi‐
lation 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 Environ‐
ment 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 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 encoun‐
tered indicates a problem in the native code, and the Java Virtual Machine will ter‐
minate 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 OutOfMemoryEr‐
ror 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 capac‐
ity 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 sys‐
tem and logging will continue on the truncated file. This option overrides -ver‐
bose: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 kilo‐
bytes, 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.ora‐
cle.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 kilo‐
bytes, 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/tech‐
notes/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 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 shut‐
down 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 unexpected Java VM ter‐
mination. 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 signals 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 terminated.
-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 -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 espe‐
cially 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 sometimes 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 speci‐
fication. However, only a restricted subset of the possible release specifications repre‐
sent 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, 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).
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)
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