java - the Java application launcher
java [ options ] class [ argument ... ]
java [ options ] -jar file.jar [ argument ... ]
options- Command-line options.
class- Name of the class to be invoked.
file.jar- Name of the jar file to be invoked. Used only with
-jar.
argument- Argument passed to the main function.
The java tool launches a Java application. It does this by starting a Java runtime environment, loading a specified class, and invoking 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 must look like the following:
public static void main(String args[])
By default, the first non-option argument is the name of the class to be invoked. A fully-qualified class name should be used. If the -jar option is specified, the first non-option argument is the name of a JAR archive 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 launcher has a set of standard
options that are supported on the current runtime
environment and will be supported in future releases. In
addition, the current implementations of the virtual machines
support a set of non-standard
options that are subject to change in future releases.
- -client
- Select the Java HotSpot Client VM. A 64-bit capable jdk
currently ignores this option and instead uses the Java
Hotspot Server VM.
For default VM selection, see Server-Class Machine
Detection
- -server
- Select 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 VM selection, see Server-Class Machine
Detection
- -agentlib:libname[=options]
-
Load native agent library libname, e.g.
-agentlib:hprof
-agentlib:jdwp=help
-agentlib:hprof=help
For more information, see JVMTI Agent Command Line Options.
- -agentpath:pathname[=options]
- Load a native agent library by full pathname. For more
information, see JVMTI Agent Command
Line Options.
- -classpath classpath
- -cp classpath
-
Specify a list of directories, JAR archives, and ZIP
archives to search for class files. Class path entries are
separated by 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, the user class path consists
of the current directory (.).
As a special convenience, a class path element containing a basename 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 foo contains a.jar and b.JAR, then the
class path element foo/* 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 classpath 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 classpath wildcard expansion occurs before the
Java virtual machine is started -- no Java program will ever see
unexpanded wildcards except by querying the environment. For example; by invoking
System.getenv("CLASSPATH").
For more information on class paths, see Setting the Class Path.
- -Dproperty=value
- Set a system property value.
- -d32
- -d64
-
Request that the program to be run in a 32-bit or 64-bit environment,
respectively. If the requested environment is not installed or
is not supported, an error is reported.
Currently only the Java HotSpot Server VM supports
64-bit operation, and the "-server" option is implicit with
the use of -d64. And the "-client" option is ignored with
the use of -d64. This is subject to change in a future
release.
If neither -d32 nor -d64 is specified, the
default is to run in a 32-bit environment, except for
64-bit only systems. This is subject to change in a future
release.
- -enableassertions[:<package name>"..." | :<class name> ]
- -ea[:<package name>"..." | :<class name> ]
- -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
simply "...", 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. A
separate switch is provided to enable asserts in all system
classes; see -disablesystemassertions below.
-
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
simply "...", 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 line contains multiple instances of
these switches, 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. A
separate switch is provided to enable asserts in all system
classes; see -enablesystemassertions below.
- -enablesystemassertions
- -esa
- Enable asserts in all system classes (sets the default
assertion status for system classes to
true).
- -disablesystemassertions
- -dsa
-
Disables asserts in all system classes.
- -help or -?
- Display usage information and exit.
- -jar
-
Execute a program encapsulated in a JAR file. The first
argument is the name of a JAR file instead of a startup
class name. In order for this option to work, the manifest
of the JAR file must contain a line of the form
Main-Class: classname. Here, classname
identifies the class having the
public static void main(String[] args)
method that serves as your application's starting point.
See the Jar tool reference page and
the Jar trail of the Java
Tutorial for information about working with Jar files
and Jar-file manifests.
When you use this option, the JAR file is the source of
all user classes, and other user class path settings are
ignored.
Note that 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". Refer to Java Archive (JAR)
Files.
- -javaagent:jarpath[=options]
- Load a Java programming language agent, see
java.lang.instrument.
- -jre-restrict-search
- Include user-private JREs in the version search.
- -no-jre-restrict-search
- Exclude user-private JREs in the version search.
- -showversion
- Display version information and continue. (See also -version.)
- -splash:imagepath
- Show splash screen with image specified by imagepath.
- -verbose
- -verbose:class
- Display information about each class loaded.
- -verbose:gc
- Report on each garbage collection event.
- -verbose:jni
- Report information about use of native methods and other
Java Native Interface activity.
- -version
- Display version information and exit. (See also -showversion.)
-
-version:release
-
Specifies that the version specified by release is
required by the class or jar file specified on the command
line. If the version of the java command invoked does not
meet this specification and an appropriate implementation
is found on the system, the appropriate implementation will
be used.
release not only can specify an exact version, but can also specify 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 a star (*), a version-id followed by
a plus sign (+) , or two version-ranges combined using an ampersand (&). The star means prefix match,
the plus sign means this version or greater, and the ampersand means the logical anding of the two
version-ranges. For example:
-version:"1.6.0_13 1.6*&1.6.0_10+"
The meaning of the above 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 may be found in
Appendix A of the Java Network Launching Protocol & API Specification (JSR-56).
For jar files, the usual preference is to specify version requirements in the jar file manifest
rather than on the command line.
See the following NOTES section for important policy information on the use of this option.
- -X
- Display information about non-standard options and
exit.
- -Xint
- Operate in interpreted-only mode. Compilation to native
code is disabled, and all bytecodes are executed by the
interpreter. The performance benefits offered by the Java
HotSpot VMs' adaptive compiler will not be present in this
mode.
- -Xbatch
- Disable background compilation. Normally the VM will
compile 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
- Specify a colon-separated list of directories, JAR
archives, 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. Note: Applications that use this option
for the purpose of overriding a class in rt.jar should not be
deployed as doing so would contravene the Java Runtime
Environment binary code license.
- -Xbootclasspath/a:path
- Specify a colon-separated path of directires, JAR
archives, and ZIP archives to append to the default bootstrap
class path.
- -Xbootclasspath/p:path
- Specify a colon-separated path of directires, JAR
archives, and ZIP archives to prepend in front of the default
bootstrap class path. Note: Applications that use this
option for the purpose of overriding a class in rt.jar should
not be deployed as doing so would contravene the Java
Runtime Environment binary code license.
- -Xcheck:jni
- Perform additional checks for Java Native Interface (JNI)
functions. Specifically, the Java Virtual Machine validates
the parameters passed to the JNI function as well as 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
- Perform strict class-file format checks. For purposes of
backwards compatibility, the default format checks performed
by the JDK's virtual machine are no stricter than the
checks performed by 1.1.x versions of the JDK software. The
-Xfuture flag 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
- Disable class garbage collection. Use of this option will
prevent memory recovery from loaded classes thus increasing
overall memory usage. This could cause OutOfMemoryError to be
thrown in some applications.
- -Xincgc
- Enable the incremental garbage collector. The incremental
garbage collector, which is 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
-
Report on each garbage collection event, as with
-verbose:gc, but log this data to file. In addition
to the information -verbose:gc gives, each
reported event will be preceeded 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 JVM 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 if both are given on the
command line.
- -Xmnsize or -XX:NewSize
- Sets the size of the young generation (nursery).
- -Xmsn
-
Specify the initial size, in bytes, of the memory
allocation pool. This value must be a multiple of 1024
greater than 1MB. 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 more information, see HotSpot Ergonomics
Examples:
-Xms6291456
-Xms6144k
-Xms6m
- -Xmxn
-
Specify the maximum size, in bytes, of the memory
allocation pool. This value must a multiple of 1024 greater
than 2MB. 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 more information, see HotSpot Ergonomics
Examples:
-Xmx83886080
-Xmx81920k
-Xmx80m
On Solaris 7 and Solaris 8 SPARC platforms,
the upper limit for this value is approximately 4000m minus
overhead amounts. On Solaris 2.6 and x86 platforms, the
upper limit is approximately 2000m minus overhead amounts.
On Linux platforms, the upper limit is approximately 2000m
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 virtual
machine (JVM).
In a previous release, the Shutdown Hooks facility was
added to allow orderly shutdown of a Java application. The
intent was to allow user cleanup code (such as closing
database connections) to run at shutdown, even if the JVM
terminates abruptly.
Sun's JVM catches signals to implement shutdown hooks
for abnormal JVM termination. The JVM uses SIGHUP, SIGINT,
and SIGTERM to initiate the running of shutdown hooks.
The JVM uses a similar mechanism to implement the
pre-1.2 feature of dumping thread stacks for debugging
purposes. Sun's JVM uses SIGQUIT to perform thread
dumps.
Applications embedding the JVM frequently need to trap
signals like SIGINT or SIGTERM, which can lead to
interference with the JVM's own signal handlers. The
-Xrs command-line option is available to address
this issue. When -Xrs is used on Sun's JVM, the
signal masks for SIGINT, SIGTERM, SIGHUP, and SIGQUIT are
not changed by the JVM, and signal handlers for these
signals are not installed.
There are two consequences of specifying
-Xrs:
- SIGQUIT thread dumps are not available.
- User code is responsible for causing shutdown hooks
to run, for example by calling System.exit() when the JVM
is to be terminated.
- -Xssn
- Set thread stack size.
- -XX:AllocationPrefetchStyle=n
- Sets the style of prefetch used during allocation. default=2.
- -XX:+AggressiveOpts
- Enables aggressive optimization.
- -XX:+|-DisableAttachMechanism
- This option specifies whether tools (such as
jmap and jconsole) are allowed to attach
to the JVM. By default, this feature is disabled. That is, attaching
is enabled. Example usage:
java -XX:+DisableAttachMechanism
- -XXLargePageSizeInBytes=n
- This option 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 JVM 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 usage:
java -XX:+UnlockExperimentalVMOptions -XX:PredictedClassLoadCount=60013
- -XX:+PrintCompilation
- Prints verbose output from the HotSpot 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 HotSpot GC is impacted by the software reference count.
- -XX:TLABSize=n
- Thread local allocation buffers (TLAB) are enabled by default in HotSpot. HotSpot automatically sizes TLABs based on allocation patterns. The -XX:TLABSize option allows 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 Oracle Java SE Products web page.
If this flag is not specified, the default is to run the Java virtual machine without the commercial features being available.
Once they are enabled, it is not possible to disable their use at runtime.
- -XX:+UseAltSigs
- The VM uses SIGUSR1 and SIGUSR2 by
default, which can sometimes conflict with applications that
signal-chain SIGUSR1 and SIGUSR2. The
-XX:+UseAltSigs option will cause the VM to use
signals other than SIGUSR1 and SIGUSR2 as
the default.
- -XX:+|-UseCompressedOops
- Enables compressed references in 64-bit JVMs.
This option is true by default.
- -XX:+UseConcMarkSweepGC or -XX:+UseG1GC
- These flags enable either the Concurrent Mark Sweep (CMS) or the G1 garbage collectors.
- -XX:+|-UseLargePages
- Use this flag to enable 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.
The -version:release command line 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:
- Any version, represented by not using this option.
- Any version greater than an arbitrarily precise version-id. 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.
-
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*"
-
"Or" expressions of items 2. or 3. above. 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 previous releases.
The following examples show how to use experimental tuning flags to optimize either throughput or faster response time.
java -d64 -server -XX:+AggressiveOpts -XX:+UseLargePages -Xmn10g -Xms26g -Xmx26g
java -d64 -XX:+UseG1GC -Xms26g Xmx26g -XX:MaxGCPauseMillis=500 -XX:+PrintGCTimeStamps
The following exit values are generally 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
