java

You can use the java command to launch a Java application.

Synopsis

To execute a class:

java [options] mainclass [args...]

To execute a JAR file:

java [options] -jar jarfile [args...]

To execute the main class in a module:

java [options] [--module-path modulepath] --module module[/mainclass] [args...]

options: Specifies command-line options separated by spaces. See Overview of Java Options for a description of available options.
mainclass: Specifies the name of the class to be launched. Command-line entries following classname are the arguments for the main method.
jarfile: Specifies the name of the Java Archive (JAR) file to be called. Used only with the -jar option.
modulepath: Specifies the path to a semicolon-separated (;) list of directories in which each directory is a directory of modules Used only with the --module-path option. See Standard Options for Java.
module[/mainclass]: Specifies the name of the initial module to resolve and, if it isn’t specified by the module, then specifies the name of the mainclass to execute. Used only with the -m or --module option. See Standard Options for Java.
args: Specifies the arguments passed to the main method separated by spaces.

Note:

Arguments following the main class, -jar jarfile , -m or --module module/mainclass are passed as the arguments to the main class.

Description

The java command starts a Java application. It does this by starting the Java Runtime Environment (JRE), loading the 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)

In JDK 9, a new launcher environment variable, JDK_JAVA_OPTIONS, has been introduced that prepends its content to the actual command line of the java launcher. See Using the JDK_JAVA_OPTIONS Launcher Environment Variable.

The java command can be used to launch a JavaFX application by loading a class that either has a main() method or that extends the javafx.application.Application. In the latter case, the launcher constructs an instance of the Application class, calls its init() method, and then calls the start(javafx.stage.Stage) method.

By default, the first argument that isn’t an option of the java command is the fully qualified name of the class to be called. If the -jar option is specified, then 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 Main-Class manifest header in its manifest file.

Arguments after the class file name or the JAR file name are passed to the main() method.

Windows: The javaw command is identical to java, except that with javaw there’s no associated console window. Use javaw when you don’t want a command prompt window to appear. The javaw launcher will, however, display a dialog box with error information if a launch fails.

Using the JDK_JAVA_OPTIONS Launcher Environment Variable

JDK_JAVA_OPTIONS prepends its content to the options parsed from the command line. The content of the JDK_JAVA_OPTIONS environment variable is a list of arguments separated by white-space characters (as determined by isspace()). These are prepended to the command line arguments passed to java launcher. The encoding requirement for the environment variable is the same as the java command line on the system. JDK_JAVA_OPTIONS environment variable content is treated in the same manner as that specified in the command line.

Single (') or double (") quotes can be used to enclose arguments that contain whitespace characters. All content between the open quote and the first matching close quote are preserved by simply removing the pair of quotes. In case a matching quote is not found, the launcher will abort with an error message. @files are supported as they are specified in the command line. However, as in @files, use of a wildcard is not supported. In order to mitigate potential misuse of JDK_JAVA_OPTIONS behavior, options that specify the main class (such as -jar) or cause the java launcher to exit without executing the main class (such as -h) are disallowed in the environment variable. If any of these options appear in the environment variable, the launcher will abort with an error message. When JDK_JAVA_OPTIONS is set, the launcher prints a message to stderr as a reminder.

Example:

export JDK_JAVA_OPTIONS='-g @file1 -Dprop=value @file2 -Dws.prop="white spaces”' 
$ java -Xint @file3

is equivalent to the command line:

java -g @file1 -Dprop=value @file2 -Dws.prop="white spaces" -Xint @file3

Overview of Java Options

The java command supports a wide range of options in the following categories:

Standard Options for Java: Options guaranteed to be supported by all implementations of the Java Virtual Machine (JVM). They’re used for common actions, such as checking the version of the JRE, setting the class path, enabling verbose output, and so on.
Extra Options for Java: General purpose options that are specific to the Java HotSpot Virtual Machine. They aren’t guaranteed to be supported by all JVM implementations, and are subject to change. These options start with -X.

The advanced options aren’t 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. Several examples of performance tuning are provided in Performance Tuning Examples. These options aren’t guaranteed to be supported by all JVM implementations and are subject to change. Advanced options start with -XX.

Advanced Runtime Options for Java: Control the runtime behavior of the Java HotSpot VM.
Advanced JIT Compiler Options for java: Control the dynamic just-in-time (JIT) compilation performed by the Java HotSpot VM.
Advanced Serviceability Options for Java: Enable gathering system information and performing extensive debugging.
Advanced Garbage Collection Options for Java: Control how garbage collection (GC) is performed by the Java HotSpot

Boolean options are used to either enable a feature that’s disabled by default or disable a feature that’s enabled by default. Such options don’t require a parameter. Boolean -XX options are enabled using the plus sign (-XX:+OptionName) and disabled using the minus sign (-XX:-OptionName).

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’re expected to specify the size in bytes, then you can use no suffix, or use the suffix k or K for kilobytes (KB), m or M for megabytes (MB), or g or G for gigabytes (GB). For example, to set the size to 8 GB, you can specify either 8g, 8192m, 8388608k, or 8589934592 as the argument. If you are expected to specify the percentage, then use a number from 0 to 1. For example, specify 0.25 for 25%.

The following sections describe the options that are obsolete, deprecated, and removed in JDK 9:

Obsolete Java Options: Accepted but ignored. A warning is issued when they’re used.
Deprecated Java Options: Accepted and acted upon. A warning is issued when they’re used.
Removed Java Options: Removed in JDK 9. Using them results in an error.

Standard Options for Java

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

Note:

To specify an argument for a long option, you can use either --name=value or --name value.

-agentlib:libname[=options]

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

Oracle Solaris, Linux, and OS X: If the option -agentlib:foo is specified, then the JVM attempts to load the library named libfoo.so in the location specified by the LD_LIBRARY_PATH system variable (on OS X this variable is DYLD_LIBRARY_PATH).
Windows: If the option -agentlib:foo is specified, then the JVM attempts to load the library named foo.dll in the location specified by the PATH system variable.

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:
```
-agentlib:jdwp=transport=dt_socket,server=y,address=8000
```

-agentpath:pathname[=options]

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

--class-path classpath, -classpath classpath , or -cp classpath

A semicolon (;) separated list of directories, JAR archives, and ZIP archives to search for class files.

Specifying classpath overrides any setting of the CLASSPATH environment variable. If the class path option isn’t used and classpath isn’t 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 an asterisk (*) is considered equivalent to specifying a list of all the files in the directory with the extension .jar or .JAR . A Java program can’t tell the difference between the two invocations. For example, if the directory mydir contains a.jar and b.JAR, then the class path element mydir/* is expanded to 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 of an asterisk (*) expands to a list of all the jar files in the current directory. The CLASSPATH environment variable, where defined, is similarly expanded. Any class path wildcard expansion that occurs before the Java VM is started. Java programs never see wildcards that aren’t expanded except by querying the environment, such as by calling System.getenv("CLASSPATH").

--disable-@files

Can be used anywhere on the command line, including in an argument file, to prevent further @filename expansion. This option stops expanding @argfiles after the option.

--module-path modulepath... or -p modulepath

Searches for directories from a semicolon-separated (;) list of directories. Each directory is a directory of modules.

--upgrade-module-path modulepath...

Searches for directories from a semicolon-separated (;) list of directories. Each directory is a directory of modules that replace upgradeable modules in the runtime image.

--add-modules module[,module...]

Specifies the root modules to resolve in addition to the initial module. module also can be ALL-DEFAULT, ALL-SYSTEM, and ALL-MODULE-PATH.

--list-modules

Lists the observable modules and then exits.

-d module or --describe-module module

Describes a specified module and then exits.

--dry-run

Creates the VM but doesn’t execute the main method. This --dry-run option might be useful for validating the command-line options such as the module system configuration.

--validate-modules

Validates all modules and exit. This option is helpful for finding conflicts and other errors with modules on the module path.

-Dproperty=value

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

-disableassertions[:[packagename]...|:classname] or -da[:[packagename]...|:classname]

Disables assertions. By default, assertions are disabled in all packages and classes. With no arguments, -disableassertions (-da) disables assertions in all packages and classes. With the packagename argument ending in ..., the switch disables assertions in the specified package and any subpackages. If the argument is simply ..., then the switch disables assertions in the unnamed package in the current working directory. With the classname argument, the switch disables assertions in the specified class.

The -disableassertions (-da) option applies to all class loaders and to system classes (which don’t have a class loader). There’s one exception to this rule: If the option is provided with no arguments, then it doesn’t apply to system classes. This makes it easy to disable assertions in all classes except for system classes. The -disablesystemassertions option enables you to disable assertions in all system classes. To explicitly enable assertions in specific packages or classes, use the -enableassertions (-ea) option. Both options can be used at the same time. For example, to run the MyClass application with assertions enabled in the package com.wombat.fruitbat (and any subpackages) but disabled in the class com.wombat.fruitbat.Brickbat, use the following command:

java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat MyClass

-disablesystemassertions or -dsa

Disables assertions in all system classes.

-enableassertions[:[packagename]...|:classname] or -ea[:[packagename]...|:classname]

Enables assertions. By default, assertions are disabled in all packages and classes. With no arguments, -enableassertions (-ea) enables assertions in all packages and classes. With the packagename argument ending in ..., the switch enables assertions in the specified package and any subpackages. If the argument is simply ..., then the switch enables assertions in the unnamed package in the current working directory. With the classname argument, the switch enables assertions in the specified class.

The -enableassertions (-ea) option applies to all class loaders and to system classes (which don’t have a class loader). There’s one exception to this rule: If the option is provided with no arguments, then it doesn’t apply to system classes. This makes it easy to enable assertions in all classes except for system classes. The -enablesystemassertions option provides a separate switch to enable assertions in all system classes. To explicitly disable assertions in specific packages or classes, use the -disableassertions (-da) option. If a single command contains multiple instances of these switches, then they’re processed in order, before loading any classes. For example, to run the MyClass application with assertions enabled only in the package com.wombat.fruitbat (and any subpackages) but disabled in the class com.wombat.fruitbat.Brickbat, use the following command:

java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat MyClass

-enablesystemassertions or -esa

Enables assertions in all system classes.

-help or -?

Prints the help message to the error stream.

--help

Prints the help message to the output stream.

-jar filename

Executes a program encapsulated in a JAR file. The filename argument is the name of a JAR file with a manifest that contains a line in the form Main-Class:classname that defines the class with the public static void main(String[] args) method that serves as your application's starting point. When you use the -jar option, the specified JAR file is the source of all user classes, and other class path settings are ignored. If you’re using JAR files, then see: jar

-javaagent:jarpath[=options]

Loads the specified Java programming language agent.

--show-version or -showversion

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

--show-module-resolution

Shows module resolution output during startup.

-splash:imgname

Shows the splash screen with the image specified by imgname. HiDPI scaled images are automatically supported and used if available. The unscaled image file name, such as image.ext, should always be passed as the argument to the -splash option. The most appropriate scaled image provided is picked up automatically.

For example, to show the splash.gif file from the images directory when starting your application, use the following option:

-splash:images/splash.gif

-verbose:class

Displays information about each loaded class.

-verbose:gc

Displays information about each garbage collection (GC) event.

-verbose:jni

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

-verbose:module

Displays information about the modules in use.

--version or -version

Displays version information and then exits. This option is equivalent to the -showversion option except that the latter doesn’t instruct the JVM to exit after displaying version information.

-X

Prints the help on extra options to the error stream.

--help-extra

Prints the help on extra options to the output stream.

@argument files

Specifies one or more argument files prefixed by @ used by the java command. It isn’t uncommon for the java command line to be very long because of the .jar files needed in the classpath. The @argument files option overcomes command-line length limitations by enabling the launcher to expand the contents of argument files after shell expansion, but before argument processing. Contents in the argument files are expanded because otherwise, they would be specified on the command line until the -Xdisable-@files option was encountered.

The argument files can also contain the main class name and all options. If an argument file contains all of the options required by the java command, then the command line could simply be:

java @argument files

See java Command-Line Argument Files for a description and examples of using @argument files .

Extra Options for Java

The following java options are general purpose options that are specific to the Java HotSpot Virtual Machine.

-Xbatch

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 -Xbatch flag disables background compilation so that compilation of all methods proceeds as a foreground task until completed. This option is equivalent to -XX:-BackgroundCompilation.

-Xbootclasspath/a:directories| zip|JAR files

Specifies a list of directories, JAR files, and ZIP archives to append to the end of the default bootstrap class path.

Oracle Solaris, Linux, and OS X: Colons (:) separate entities in this list.

Windows: Semicolons (;) separate entities in this list.

-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. It also checks for pending exceptions between JNI calls. Any invalid data encountered indicates a problem in the native code, and the JVM terminates with an irrecoverable error in such cases. Expect a performance degradation when this option is used.

-Xcomp

Forces compilation of methods on first invocation. By default, the Client VM (-client) performs 1,000 interpreted method invocations and the Server VM (-server) performs 10,000 interpreted method invocations to gather information for efficient compilation. Specifying the -Xcomp option disables interpreted method invocations to increase compilation performance at the expense of efficiency. You can also change the number of interpreted method invocations before compilation using the -XX:CompileThreshold option.

-Xdebug

Does nothing. Provided for backward compatibility.

-Xdiag

Shows additional diagnostic messages.

-Xfuture

Enables strict class-file format checks that enforce close conformance to the class-file format specification. Developers should use this flag when developing new code. Stricter checks may become the default in future releases.

-Xint

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 aren’t present in this mode.

-Xinternalversion

Displays more detailed JVM version information than the -version option, and then exits.

-Xloggc:option

Enables the JVM unified logging framework. Logs GC status to a file with time stamps.

-Xlog:option

Configure or enable logging with the Java Virtual Machine (JVM) unified logging framework. See Enable Logging with the JVM Unified Logging Framework.

-Xmixed

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

-Xmn size

Sets the initial and maximum size (in bytes) of the heap for the young generation (nursery). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, or g or G 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 are performed. If the size is too large, then only full garbage collections are performed, which can take a long time to complete. Oracle recommends that you keep the size for the young generation greater than 25% and less than 50% 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:

-Xmn256m
-Xmn262144k
-Xmn268435456

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

-Xms size

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 k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The following examples show how to set the size of allocated memory to 6 MB using various units:

-Xms6291456
-Xms6144k
-Xms6m

If you don’t set this option, then the initial size is 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 -Xmn option or the -XX:NewSize option.

-Xmx size

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 k or K to indicate kilobytes, m or M to indicate megabytes, or g or G to indicate gigabytes. The default value is chosen at runtime based on system configuration. For server deployments, -Xms and -Xmx are often set to the same value. The following examples show how to set the maximum allowed size of allocated memory to 80 MB using various units:

-Xmx83886080
-Xmx81920k
-Xmx80m

The -Xmx option is equivalent to -XX:MaxHeapSize.

-Xnoclassgc

Disables garbage collection (GC) of classes. This can save some GC time, which shortens interruptions during the application run. When you specify -Xnoclassgc at startup, the class objects in the application are left untouched during GC and are always be considered live. This can result in more memory being permanently occupied which, if not used carefully, throws an out-of-memory exception.

-Xprof

Profiles the running program and sends profiling data to standard output. This option is provided as a utility that’s useful in program development and isn’t intended to be used in production systems.

-Xrs

Reduces the use of operating system signals by the JVM. Shutdown hooks enable the orderly shutdown of a Java application by running user cleanup code (such as closing database connections) at shutdown, even if the JVM terminates abruptly.

Oracle Solaris, Linux, and OS X:
- The JVM catches signals to implement shutdown hooks for unexpected termination. The JVM uses SIGHUP, SIGINT, and SIGTERM to initiate the running of shutdown hooks.
- The JVM catches signals to implement shutdown hooks for unexpected termination. The JVM uses SIGHUP, SIGINT, and SIGTERM to initiate the running of shutdown hooks.
- Applications embedding the JVM frequently need to trap signals such as SIGINT or SIGTERM, which can lead to interference with the JVM signal handlers. The -Xrs option is available to address this issue. When -Xrs is used, the signal masks for SIGINT, SIGTERM, SIGHUP, and SIGQUIT aren’t changed by the JVM, and signal handlers for these signals aren’t installed.
Windows:
- The JVM watches for console control events to implement shutdown hooks for unexpected termination. Specifically, the JVM registers a console control handler that begins shutdown-hook processing and returns TRUE for CTRL_C_EVENT, CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT, and CTRL_SHUTDOWN_EVENT.
- The JVM uses a similar mechanism to implement the feature of dumping thread stacks for debugging purposes. The JVM uses CTRL_BREAK_EVENT to perform thread dumps.
- If the JVM is run as a service (for example, as a servlet engine for a web server), then it can receive CTRL_LOGOFF_EVENT but shouldn’t initiate shutdown because the operating system doesn’t actually terminate the process. To avoid possible interference such as this, the -Xrs option can be used. When the -Xrs option is used, the JVM doesn’t install a console control handler, implying that it doesn’t watch for or process CTRL_C_EVENT, CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT, or CTRL_SHUTDOWN_EVENT.

There are two consequences of specifying -Xrs:

Oracle Solaris, Linux, and OS X: SIGQUIT thread dumps aren’t available.
Windows: Ctrl + Break thread dumps aren’t available.

User code is responsible for causing shutdown hooks to run, for example, by calling the System.exit() when the JVM is to be terminated.

-Xshare:mode

Sets the class data sharing (CDS) mode.

Possible mode arguments for this option include the following:

auto: Uses CDS if possible. This is the default value for Java HotSpot 32-Bit Client VM.
on: Requires the use of CDS. This option prints an error message and exits if class data sharing can’t be used.
off: Instructs not to use CDS.

-XshowSettings

Shows all settings and then continues.

-XshowSettings:category

Shows settings and continues. Possible category arguments for this option include the following:

all: Shows all categories of settings. This is the default value.
locale: Shows settings related to locale.
properties: Shows settings related to system properties.
vm: Shows the settings of the JVM.

-Xss size

Sets the thread stack size (in bytes). Append the letter k or K to indicate KB, m or M to indicate MB, or g or G to indicate GB. The default value depends on the platform:

Linux/x64 (64-bit): 1024 KB
OS X (64-bit): 1024 KB
Oracle Solaris/x64 (64-bit): 1024 KB
Windows: The default value depends on virtual memory

The following examples set the thread stack size to 1024 KB in different units:

-Xss1m
-Xss1024k
-Xss1048576

This option is similar to -XX:ThreadStackSize.

-Xverify:mode

Sets the mode of the bytecode verifier. Bytecode verification ensures that class files are properly formed and satisfy the constraints listed in Verification of Class Files in the The Java Virtual Machine Specification.

Don’t turn off verification because this reduces the protection provided by Java and could cause problems due to ill-formed class files.

Possible mode arguments for this option include the following:

remote: Verifies those classes that aren’t loaded by the bootstrap class loader. This is the default behavior if you don’t specify the -Xverify option.
all: Enables verification of all bytecodes.
none: Disables verification of all bytecodes. Use of -Xverify:none is unsupported.

--add-reads module=target-module(,target-module)*

Updates module to read the target-module, regardless of the module declaration. target-module can be all unnamed to read all unnamed modules.

--add-exports module/package=target-module(,target-module)*

Updates module to export package to target-module, regardless of module declaration. The target-module can be all unnamed to export to all unnamed modules.

--add-opens module/package=target-module(,target-module)*

Updates module to open package to target-module, regardless of module declaration.

--illegal-access=parameter

Note:

This option is a new option in JDK 9 and may not be available in future JDK versions.

When present at run time, --illegal-access= takes a keyword parameter to specify a mode of operation:

Note:

Illegal-access operations to internal APIs from code on the class path are allowed by default in JDK 9.

permit: This mode opens packages in JDK 9 that existed in JDK 8 to code on the class path. This allows code on class path that relies on the use of setAccessible to break into JDK internals, or to do other illegal access on members of classes in these packages, to work as per previous releases. This enables both static access (such as, by compiled bytecode) and deep reflective access. Deep reflective access is accomplished through the platform's reflection APIs. The first reflective-access operation to any such package causes a warning to be issued. However, no warnings are issued after the first occurrence. This single warning describes how to enable further warnings. This mode is the default for JDK 9 but will change in a future release.
warn: This mode is identical to permit except that a warning message is issued for each illegal reflective-access operation.
debug: This mode is identical to warn except that both a warning message and a stack trace are issued for each illegal reflective-access operation.
deny: This mode disables all illegal-access operations except for those enabled by other command-line options, such as--add-opens. This mode will become the default in a future release.

The default mode, --illegal-access=permit, is intended to make you aware of code on the class path that reflectively accesses any JDK-internal APIs at least once. To learn about all such accesses, you can use the warn or the debug modes. For each library or framework on the class path that requires illegal access, you have two options:

If the component's maintainers have already released a fixed version that no longer uses JDK-internal APIs then you can consider upgrading to that version.
If the component still needs to be fixed, then you can contact its maintainers and ask them to replace their use of JDK-internal APIs with the proper exported APIs.

If you must continue to use a component that requires illegal access, then you can eliminate the warning messages by using one or more --add-opens options to open only those internal packages to which access is required.

To verify that your application is ready for a future version of the JDK, run it with --illegal-access=deny along with any necessary --add-opens options. Any remaining illegal-access errors will most likely be due to static references from compiled code to JDK-internal APIs. You can identify those by running the jdeps tool with the --jdk-internals option. For performance reasons, JDK 9 does not issue warnings for illegal static-access operations.

--limit-modules module[,module...]

Specifies the limit of the universe of observable modules.

--patch-module module=file(;file)*

Overrides or augments a module with classes and resources in JAR files or directories.

--disable-@files

Can be used anywhere on the command line, including in an argument file, to prevent further @filename expansion. This option stops expanding @argfiles after the option.

Extra Options for Mac OS X

The following extra options are Mac OS X specific.

-XstartOnFirstThread: Runs the main() method on the first (AppKit) thread.
-Xdock:name=application name: Overrides the default application name displayed in dock.
-Xdock:icon=path to icon file: Overrides the default icon displayed in dock.

Advanced Runtime Options for Java

These java options control the runtime behavior of the Java HotSpot VM.

-XX:+CheckEndorsedAndExtDirs

Enables the option to prevent the java command from running a Java application if any of these directories exists and isn't empty:

lib/endorsed
lib/ext
The systemwide platform-specific extension directory

The endorsed standards override mechanism and the extension mechanism are no longer supported.

-XX:-CompactStrings

Disables the Compact Strings feature. By default, this option is enabled. When this option is enabled, Java Strings containing only single-byte characters are internally represented and stored as single-byte-per-character Strings using ISO-8859-1 / Latin-1 encoding. This reduces, by 50%, the amount of space required for Strings containing only single-byte characters. For Java Strings containing at least one multibyte character: these are represented and stored as 2 bytes per character using UTF-16 encoding. Disabling the Compact Strings feature forces the use of UTF-16 encoding as the internal representation for all Java Strings.

Cases where it may be beneficial to disable Compact Strings include the following:

When it’s known that an application overwhelmingly will be allocating multibyte character Strings
In the unexpected event where a performance regression is observed in migrating from Java SE 8 to Java SE 9 and an analysis shows that Compact Strings introduces the regression

In both of these scenarios, disabling Compact Strings makes sense.

-XX:CompilerDirectivesFile=file

Adds directives from a file to the directives stack when a program starts. See Compiler Directives and the Command Line.

-XX:CompilerDirectivesPrint

Prints the directives stack when the program starts or when a new directive is added..

-XX:ConcGCThreads=n

Sets the number of parallel marking threads. Sets n to approximately 1/4 of the number of parallel garbage collection threads (ParallelGCThreads).

-XX:+DisableAttachMechanism

Disables the mechanism that lets tools attach to the JVM. By default, this option is disabled, meaning that the attach mechanism is enabled and you can use diagnostics and troubleshooting tools such as jcmd, jstack, jmap, and jinfo.

Note:

The tools such as jcmd, jinfo, jmap, and jstack shipped with the JDK aren’t supported when using the tools from one JDK version to troubleshoot a different JDK version.

-XX:ErrorFile=filename

Specifies the path and file name to which error data is written when an irrecoverable error occurs. By default, this file is created in the current working directory and named hs_err_pid pid.log where pid is the identifier of the process that caused the error.

The following example shows how to set the default log file (note that the identifier of the process is specified as %p):

-XX:ErrorFile=./hs_err_pid%p.log

Oracle Solaris, Linux, and OS X: The following example shows how to set the error log to /var/log/java/java_error.log:
```
-XX:ErrorFile=/var/log/java/java_error.log
```
Windows: The following example shows how to set the error log file to C:/log/java/java_error.log:
```
-XX:ErrorFile=C:/log/java/java_error.log
```

If the file can ‘t be created in the specified directory (due to insufficient space, permission problem, or another issue), then the file is created in the temporary directory for the operating system:

Oracle Solaris, Linux, and OS X: The temporary directory is /tmp.
Windows: The temporary directory is specified by the value of the TMP environment variable; if that environment variable isn’t defined, then the value of the TEMP environment variable is used.

-XX:+FailOverToOldVerifier

Enables automatic failover to the old verifier when the new type checker fails. By default, this option is disabled and it’s ignored (that is, treated as disabled) for classes with a recent bytecode version. You can enable it for classes with older versions of the bytecode.

-XX:+FlightRecorder

.Enables the use of the Java Flight Recorder (JFR) during the runtime of the application. This is a commercial feature that requires that you also specify the -XX:+UnlockCommercialFeatures option as follows:

java -XX:+UnlockCommercialFeatures -XX:+FlightRecorder

Note:

The -XX:+FlightRecorder option is no longer required to use JFR. This was a change made in JDK 8u40.

-XX:FlightRecorderOptions=parameter=value

Sets the parameters that control the behavior of JFR. This is a commercial feature that works in conjunction with the -XX:+UnlockCommercialFeatures option. The -XX:+FlightRecorder option is no longer required to use JFR. This was a change made in JDK 8u40.

The following list contains all available JFR parameters:

globalbuffersize=size: Specifies the total amount of primary memory (in bytes) used for data retention. Append k or K, to specify the size in KB, m or M to specify the size in MB, or g or G to specify the size in GB. By default, the size is set to 462848 bytes.
loglevel={quiet|error|warning|info|debug|trace}: Specify the amount of data written to the log file by JFR. By default, it’s set to info.
maxchunksize=size: Specifies the maximum size (in bytes) of the data chunks in a recording. Append k or K, to specify the size in KB, or m or M to specify the size in MB, or g or G to specify the size in GB. By default, the maximum size of data chunks is set to 12 MB.
memorysize=size: Determines how much buffer memory should be used.
repository=path: Specifies the repository (a directory) for temporary disk storage. By default, the system's temporary directory is used.
samplethreads={true|false}: Specifies whether thread sampling is enabled. Thread sampling occurs only if the sampling event is enabled along with this parameter. By default, this parameter is enabled.
stackdepth=depth: Stack depth for stack traces by JFR. By default, the depth is set to 64 method calls. The maximum is 2048, and the minimum is 1.
threadbuffersize=size: Specifies the per-thread local buffer size (in bytes). Append k or K, to specify the size in KB, or m or M to specify the size in MB, g or G to specify the size in GB. Higher values for this parameter allow more data gathering without contention to flush it to the global storage. It can increase an application footprint in a thread-rich environment. By default, the local buffer size is set to 5 KB.
transform={true|false}: Specifies if event classes should be retransformed using JVMTI. If false, instrumentation will be added when event classes are loaded. By default it is true.

You can specify values for multiple parameters by separating them with a comma.

-XX:InitiatingHeapOccupancyPercent=45

Sets the Java heap occupancy threshold that triggers a marking cycle. The default occupancy is 45 percent of the entire Java heap.

-XX:LargePageSizeInBytes=size

Oracle Solaris: Sets the maximum size (in bytes) for large pages used for the Java heap. The size argument must be a power of 2 (2, 4, 8, 16, and so on). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, or g or G to indicate gigabytes. By default, the size is set to 0, meaning that the JVM chooses the size for large pages automatically. See Large Pages.

The following example describes how to set the large page size to 4 megabytes (MB):

-XX:LargePageSizeInBytes=4m

-XX:MaxDirectMemorySize=size

Sets the maximum total size (in bytes) of the java.nio package, direct-buffer allocations. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, or g or G to indicate gigabytes. By default, the size is set to 0, meaning that the JVM chooses the size for NIO direct-buffer allocations automatically.

The following examples illustrate how to set the NIO size to 1024 KB in different units:

-XX:MaxDirectMemorySize=1m
-XX:MaxDirectMemorySize=1024k
-XX:MaxDirectMemorySize=1048576

-XX:-MaxFDLimit

Disables the attempt to set the soft limit for the number of open file descriptors to the hard limit. By default, this option is enabled on all platforms, but is ignored on Windows. The only time that you may need to disable this is on Mac OS, where its use imposes a maximum of 10240, which is lower than the actual system maximum.

-XX:MaxGCPauseMillis=200

Sets a target value for the desired maximum pause time. The default value is 200 milliseconds. The specified value doesn’t adapt to your heap size.

-XX:NativeMemoryTracking=mode

Specifies the mode for tracking JVM native memory usage. Possible mode arguments for this option include the following:

off: Instructs not to track JVM native memory usage. This is the default behavior if you don’t specify the -XX:NativeMemoryTracking option.
summary: Tracks memory usage only by JVM subsystems, such as Java heap, class, code, and thread.
detail: In addition to tracking memory usage by JVM subsystems, track memory usage by individual CallSite, individual virtual memory region and its committed regions.

-XX:ObjectAlignmentInBytes=alignment

Sets the memory alignment of Java objects (in bytes). By default, the value is set to 8 bytes. The specified value should be a power of 2, and must be within the range of 8 and 256 (inclusive). This option makes it possible to use compressed pointers with large Java heap sizes.

The heap size limit in bytes is calculated as:

4GB * ObjectAlignmentInBytes

Note:

As the alignment value increases, the unused space between objects also increases. As a result, you may not realize any benefits from using compressed pointers with large Java heap sizes.

-XX:OnError=string

Sets a custom command or a series of semicolon-separated commands to run when an irrecoverable error occurs. If the string contains spaces, then it must be enclosed in quotation marks.

Oracle Solaris, Linux, and OS X: The following example shows how the -XX:OnError option can be used to run the gcore command to create the core image, and the debugger is started to attach to the process in case of an irrecoverable error (the %p designates the current process):
```
-XX:OnError="gcore %p;dbx - %p"
```
Windows: The following example shows how the -XX:OnError option can be used to run the userdump.exe utility to obtain a crash dump in case of an irrecoverable error (the %p designates the current process). This example assumes that the path to the userdump.exe utility is specified in the PATH environment variable:
```
-XX:OnError="userdump.exe %p"
```

-XX:OnOutOfMemoryError=string

Sets a custom command or a series of semicolon-separated commands to run when an OutOfMemoryError exception is first thrown. If the string contains spaces, then it must be enclosed in quotation marks. For an example of a command string, see the description of the -XX:OnError option.

-XX:ParallelGCThreads=n

Sets the value of the STW worker threads. Sets the value of n to the number of logical processors. The value of n is the same as the number of logical processors up to a value of 8. If there are more than 8 logical processors, then this option sets the value of n to approximately 5/8 of the logical processors. This works in most cases except for larger SPARC systems where the value of n can be approximately 5/16 of the logical processors.

-XX:+PerfDataSaveToFile

If enabled, saves jstat binary data when the Java application exits. This binary data is saved in a file named hsperfdata_pid, where pid is the process identifier of the Java application that you ran. Use thejstat command to display the performance data contained in this file as follows:

jstat -class file:///path/hsperfdata_pid

jstat -gc file:///path/hsperfdata_pid

-XX:+PrintCommandLineFlags

Enables printing of ergonomically selected JVM flags that appeared on the command line. It can be useful to know the ergonomic values set by the JVM, such as the heap space size and the selected garbage collector. By default, this option is disabled and flags aren’t printed.

-XX:+PreserveFramePointer

Selects between using the RBP register as a general purpose register (-XX:-PreserveFramePointer) and using the RBP register to hold the frame pointer of the currently executing method (-XX:+PreserveFramePointer). If the frame pointer is available, then external profiling tools (for example, Linux perf) can construct more accurate stack traces.

-XX:+PrintNMTStatistics

Enables printing of collected native memory tracking data at JVM exit when native memory tracking is enabled (see -XX:NativeMemoryTracking). By default, this option is disabled and native memory tracking data isn’t printed.

-XX:+RelaxAccessControlCheck

Decreases the amount of access control checks in the verifier. By default, this option is disabled, and it’s ignored (that is, treated as disabled) for classes with a recent bytecode version. You can enable it for classes with older versions of the bytecode.

-XX:+ResourceManagement

Enables the use of Resource Management during the runtime of the application.

This is a commercial feature that requires you to also specify the -XX:+UnlockCommercialFeatures option as follows:

java -XX:+UnlockCommercialFeatures -XX:+ResourceManagement

-XX:ResourceManagementSampleInterval=value in milliseconds

Sets the parameter that controls the sampling interval for Resource Management measurements, in milliseconds.

This option can be used only when Resource Management is enabled (that is, the -XX:+ResourceManagement option is specified).

-XX:SharedArchiveFile=path

Specifies the path and name of the class data sharing (CDS) archive file

See Application Class Data Sharing.

-XX:SharedArchiveConfigFile=shared_config_file

Specifies additional shared data added to the archive file.

-XX:SharedClassListFile=file_name

Specifies the text file that contains the names of the class files to store in the class data sharing (CDS) archive. This file contains the full name of one class file per line, except slashes (/) replace dots (.). For example, to specify the classes java.lang.Object and hello.Main, create a text file that contains the following two lines:

java/lang/Object
hello/Main

The class files that you specify in this text file should include the classes that are commonly used by the application. They may include any classes from the application, extension, or bootstrap class paths.

See Application Class Data Sharing.

-XX:+ShowMessageBoxOnError

Enables the display of a dialog box when the JVM experiences an irrecoverable error. This prevents the JVM from exiting and keeps the process active so that you can attach a debugger to it to investigate the cause of the error. By default, this option is disabled.

-XX:StartFlightRecording=parameter=value

Starts a JFR recording for the Java application. This is a commercial feature that works in conjunction with the -XX:+UnlockCommercialFeatures option. This option is equivalent to the JFR.start diagnostic command that starts a recording during runtime. You can set the following parameters when starting a JFR recording:

delay=time: Specifies the delay between the Java application launch time and the start of the recording. Append s to specify the time in seconds, m for minutes, h for hours, or d for days (for example, specifying 10m means 10 minutes). By default, there’s no delay, and this parameter is set to 0.
duration=time: Specifies the duration of the recording. Append s to specify the time in seconds, m for minutes, h for hours, or d for days (for example, specifying 5h means 5 hours). By default, the duration isn’t limited, and this parameter is set to 0.
filename=path: Specifies the path and name of the JFR recording log file.
name=identifier: Takes both the name and the identifier of a recording.
maxage=time: Specifies the maximum age of disk data to keep for the default recording. Append s to specify the time in seconds, m for minutes, h for hours, or d for days (for example, specifying 30s means 30 seconds). By default, the maximum age is set to 15 minutes (15m).
maxsize=size: Specifies the maximum size (in bytes) of disk data to keep for the default recording. Append k or K, to specify the size in KB, m or M to specify the size in MB, or g or G to specify the size in GB. By default, the maximum size of disk data isn’t limited, and this parameter is set to 0.
settings=path: Specifies the path and name of the event settings file (of type JFC). By default, the default.jfc file is used, which is located in JAVA_HOME/jre/lib/jfr.

You can specify values for multiple parameters by separating them with a comma.

-XX:ThreadStackSize=size

Sets the Java thread stack size (in kilobytes). Use of a scaling suffix, such as k, results in the scaling of the kilobytes value so that -XX:ThreadStackSize=1k sets the Java thread stack size to 1024*1024 bytes or 1 megabyte. The default value depends on the platform:

Linux/x64 (64-bit): 1024 KB
OS X (64-bit): 1024 KB
Oracle Solaris/x64 (64-bit): 1024 KB
Windows: The default value depends on the virtual memory.

The following examples show how to set the thread stack size to 1 megabyte in different units:

-XX:ThreadStackSize=1k
-XX:ThreadStackSize=1024

This option is similar to -Xss.

-XX:+UnlockCommercialFeatures

Enables the use of commercial features. Commercial features are included with Oracle Java SE Advanced or Oracle Java SE Suite packages, as defined in theOracle Java SE and Oracle Java Embedded Products page.

By default, this option is disabled and the JVM runs without the commercial features. After they're enabled for a JVM process, it isn’t possible to disable their use for that process.

-XX:+UseAppCDS

Enables application class data sharing (AppCDS). To use AppCDS, you must also specify values for the options -XX:SharedClassListFile and -XX:SharedArchiveFile during both CDS dump time (see the option -Xshare:dump) and application run time.

This is a commercial feature that requires you to also specify the -XX:+UnlockCommercialFeatures option. This is also an experimental feature; it may change in future releases.

See Application Class Data Sharing.

-XX:-UseBiasedLocking

Disables the use of biased locking. Some applications with significant amounts of uncontended synchronization may attain significant speedups with this flag enabled, but applications with certain patterns of locking may see slowdowns. .

By default, this option is enabled.

-XX:-UseCompressedOops

Disables the use of compressed pointers. By default, this option is enabled, and compressed pointers are used when Java heap sizes are less than 32 GB. When this option is enabled, object references are represented as 32-bit offsets instead of 64-bit pointers, which typically increases performance when running the application with Java heap sizes of less than 32 GB. This option works only for 64-bit JVMs.

It’s also possible to use compressed pointers when Java heap sizes are greater than 32 GB. See the -XX:ObjectAlignmentInBytes option.

XX:+UseGCLogRotation

Handles large log files. This option must be used with -Xloggc:filename.

-XX:NumberOfGClogFiles=number of files

Handles large log files. The number of files must be greater than or equal to 1. The default is 1.

-XX:GCLogFileSize=number

Handles large log files. The number can be in the form of numberM or numberK. The default is set to 512K.

-XX:+UseHugeTLBFS

Linux only: This option is the equivalent of specifying -XX:+UseLargePages. This option is disabled by default. This option pre-allocates all large pages up-front, when memory is reserved; consequently the JVM can’t dynamically grow or shrink large pages memory areas; see -XX:UseTransparentHugePages if you want this behavior.

See Large Pages.

-XX:+UseLargePages

Enables the use of large page memory. By default, this option is disabled and large page memory isn’t used.

See Large Pages.

-XX:+UseMembar

Enables issuing of membars on thread-state transitions. This option is disabled by default on all platforms except ARM servers, where it’s enabled. (It’s recommended that you don’t disable this option on ARM servers.)

-XX:+UsePerfData

Enables the perfdata feature. This option is enabled by default to allow JVM monitoring and performance testing. Disabling it suppresses the creation of the hsperfdata_userid directories. To disable the perfdata feature, specify -XX:-UsePerfData.

-XX:+UseTransparentHugePages

Linux only: Enables the use of large pages that can dynamically grow or shrink. This option is disabled by default. You may encounter performance problems with transparent huge pages as the OS moves other pages around to create huge pages; this option is made available for experimentation.

-XX:+AllowUserSignalHandlers

Enables installation of signal handlers by the application. By default, this option is disabled and the application isn’t allowed to install signal handlers.

-XX:VMOptionsFile=filename

Allows user to specify VM options in a file, for example, java -XX:VMOptionsFile=/var/my_vm_options HelloWorld.

Advanced JIT Compiler Options for java

These java options control the dynamic just-in-time (JIT) compilation performed by the Java HotSpot VM.

-XX:+AggressiveOpts

Enables the use of aggressive performance optimization features. By default, this option is disabled and experimental performance features aren’t used.

-XX:AllocateInstancePrefetchLines=lines

Sets the number of lines to prefetch ahead of the instance allocation pointer. By default, the number of lines to prefetch is set to 1:

-XX:AllocateInstancePrefetchLines=1