Java Platform, Standard Edition Tools Reference
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java

Launches a Java application.

Synopsis

java [options] classname [args]

java [options] -jar filename [args]

javaw [options] classname [args]

javaw [options] -jar filename [args]

options: Command-line options separated by spaces. See Options.
classname: The name of the class to be launched.
filename: The name of the Java Archive (JAR) file to be called. Used only with the -jar option.
args: The arguments passed to the main() method separated by spaces.

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)

The java command can be used to launch a JavaFX application by loading a class that either has a main() method or that extends 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 is not an option of the java command is the fully qualified name of the class to be called. If the -jar option is specified, its argument is the name of the JAR file containing class and resource files for the application. The startup class must be indicated by the Main-Class manifest header in its source code.

The JRE searches for the startup class (and other classes used by the application) in three sets of locations: the bootstrap class path, the installed extensions, and the user's class path.

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

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

Options

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

Standard Options
Non-Standard Options
Advanced Runtime Options
Advanced JIT Compiler Options
Advanced Serviceability Options
Advanced Garbage Collection Options

Standard options are guaranteed to be supported by all implementations of the Java Virtual Machine (JVM). They are used for common actions, such as checking the version of the JRE, setting the class path, enabling verbose output, and so on.

Non-standard options are general purpose options that are specific to the Java HotSpot Virtual Machine, so they are not guaranteed to be supported by all JVM implementations, and are subject to change. These options start with -X.

Advanced options are not recommended for casual use. These are developer options used for tuning specific areas of the Java HotSpot Virtual Machine operation that often have specific system requirements and may require privileged access to system configuration parameters. They are also not guaranteed to be supported by all JVM implementations, and are subject to change. Advanced options start with -XX.

To keep track of the options that were deprecated or removed in the latest release, there is a section named Deprecated and Removed Options at the end of the document.

Boolean options are used to either enable a feature that is disabled by default or disable a feature that is enabled by default. Such options do not require a parameter. Boolean -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 are expected to specify the size in bytes, you can use no suffix, or use the suffix k or K for kilobytes (KB), m or M for megabytes (MB), 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, use a number from 0 to 1 (for example, specify 0.25 for 25%).

Standard Options

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

-agentlib:libname[=options]

Non-Standard Options

These options are general purpose options that are specific to the Java HotSpot Virtual Machine.

-X

Displays help for all available -X options.

-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:path

Specifies a list of directories, JAR files, and ZIP archives separated by semicolons (;) to search for boot class files. These are used in place of the boot class files included in the JDK.

Do not deploy applications that use this option to override a class in rt.jar, because this violates the JRE binary code license.

-Xbootclasspath/a:path

Specifies a list of directories, JAR files, and ZIP archives separated by semicolons (;) to append to the end 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 JRE binary code license.

-Xbootclasspath/p:path

Specifies a list of directories, JAR files, and ZIP archives separated by semicolons (;) to prepend to the 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 JRE binary code license.

-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. Any invalid data encountered indicates a problem in the native code, and the JVM will terminate 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 are encouraged to use this flag when developing new code because the stricter checks will 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 are not present in this mode.

-Xinternalversion

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

-Xloggc:filename

Sets the file to which verbose GC events information should be redirected for logging. The information written to this file is similar to the output of -verbose:gc with the time elapsed since the first GC event preceding each logged event. The -Xloggc option overrides -verbose:gc if both are given with the same java command.

Example:

-Xloggc:garbage-collection.log

-Xmaxjitcodesize=size

Specifies the maximum code cache size (in bytes) for JIT-compiled code. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default maximum code cache size is 240 MB; if you disable tiered compilation with the option -XX:-TieredCompilation, then the default size is 48 MB:

-Xmaxjitcodesize=240m

This option is equivalent to -XX:ReservedCodeCacheSize.

-Xmixed

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

-Xmnsize

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, 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 will be performed. If the size is too large, then only full garbage collections will be performed, which can take a long time to complete. Oracle recommends that you keep the size for the young generation between a half and a quarter 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.

-Xmssize

Sets the minimum and 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 do not set this option, then the initial size will be 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.

Note that the -XX:InitalHeapSize option can also be used to set the initial heap size. If it appears after -Xms on the command line, then the initial heap size gets set to the value specified with -XX:InitalHeapSize.

-Xmxsize

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, 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. See the section "Ergonomics" in Java SE HotSpot Virtual Machine Garbage Collection Tuning Guide at http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.

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 will be left untouched during GC and will always be considered live. This can result in more memory being permanently occupied which, if not used carefully, will throw 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 is useful in program development and is not intended to be used in production systems.

-Xrs

Reduces the use of operating system signals by the JVM.

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

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 should not initiate shutdown because the operating system will not 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 does not install a console control handler, implying that it does not watch for or process CTRL_C_EVENT, CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT, or CTRL_SHUTDOWN_EVENT.

There are two consequences of specifying -Xrs:

Ctrl + Break 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.

-Xshare:mode

Sets the class data sharing (CDS) mode. Possible mode arguments for this option include the following:

auto

Use CDS if possible. This is the default value for Java HotSpot 32-Bit Client VM.

on

Require the use of CDS. Print an error message and exit if class data sharing cannot be used.

off

Do not use CDS. This is the default value for Java HotSpot 32-Bit Server VM, Java HotSpot 64-Bit Client VM, and Java HotSpot 64-Bit Server VM.

dump

Manually generate the CDS archive. Specify the application class path as described in "Setting the Class Path".

You should regenerate the CDS archive with each new JDK release.

-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.

-Xsssize

Sets the thread stack size (in bytes). Append the letter k or K to indicate KB, m or M to indicate MB, g or G to indicate GB. 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 section 4.10, Verification of class Files in the The Java Virtual Machine Specification.

Do not turn off verification as 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 all bytecodes not loaded by the bootstrap class loader. This is the default behavior if you do not specify the -Xverify option.
all: Enables verification of all bytecodes.
none: Disables verification of all bytecodes. Use of -Xverify:none is unsupported.

Advanced Runtime Options

These 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 it uses the endorsed-standards override mechanism or the extension mechanism. This option checks if an application is using one of these mechanisms by checking the following:

The java.ext.dirs or java.endorsed.dirs system property is set.
The lib/endorsed directory exists and is not empty.
The lib/ext directory contains any JAR files other than those of the JDK.
The system-wide platform-specific extension directory contains any JAR files.

-XX:+DisableAttachMechanism

Enables the option that 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 tools such as jcmd, jstack, jmap, and jinfo.

-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_pidpid.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

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 cannot 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. The temporary directory is specified by the value of the TMP environment variable; if that environment variable is not 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 is 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 works in conjunction with the -XX:+UnlockCommercialFeatures option as follows:

java -XX:+UnlockCommercialFeatures -XX:+FlightRecorder

If this option is not provided, Java Flight Recorder can still be enabled in a running JVM by providing the appropriate jcmd diagnostic commands.

-XX:-FlightRecorder

Disables the use of the Java Flight Recorder (JFR) during the runtime of the application. This is a commercial feature that works in conjunction with the -XX:+UnlockCommercialFeatures option as follows:

java -XX:+UnlockCommercialFeatures -XX:-FlightRecorder

If this option is provided, Java Flight Recorder cannot be enabled in a running JVM.

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

The following list contains all available JFR parameters:

defaultrecording={true|false}

Specifies whether a default continuous recording should be started for the Java application. By default, this parameter is set to false. To start a default recording automatically, set the parameter to true.

disk={true|false}

Specifies whether to write temporary data to the disk repository. By default, this parameter is set to false. To enable it, set the parameter to true.

dumponexit={true|false}

Specifies whether a dump file of JFR data should be generated when the JVM terminates in a controlled manner. By default, this parameter is set to false (dump file on exit is not generated). To enable it, set the parameter to true, and also set defaultrecording=true.

The dump file is written to the location defined by the dumponexitpath parameter.

dumponexitpath=path

Specifies the path and name of the dump file with JFR data that is created when the JVM exits in a controlled manner if you set the dumponexit=true parameter. Setting the path makes sense only if you also set defaultrecording=true.

If the specified path is a directory, the JVM assigns a file name that shows the creation date and time. If the specified path includes a file name and if that file already exists, the JVM creates a new file by appending the date and time stamp to the specified file name.

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, 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 is set to info.

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).

This parameter is valid only if you set the disk=true parameter.

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, m or M to specify the size in MB, g or G to specify the size in GB. By default, the maximum size of data chunks is set to 12 MB.

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, g or G to specify the size in GB. By default, the maximum size of disk data is not limited, and this parameter is set to 0.

This parameter is valid only if you set the disk=true parameter.

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.

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.

stackdepth=depth

Stack depth for stack traces by JFR. By default, the depth is set to 64 method calls. The maximum is 2048, minimum is 1.

threadbuffersize=size

Specifies the per-thread local buffer size (in bytes). Append k or K, to specify the size in KB, 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 application footprint in a thread-rich environment. By default, the local buffer size is set to 5 KB.

You can specify values for multiple parameters by separating them with a comma. For example, to instruct JFR to write a continuous recording to disk, and set the maximum size of data chunks to 10 MB, specify the following:

-XX:FlightRecorderOptions=defaultrecording=true,disk=true,maxchunksize=10M

-XX:LargePageSizeInBytes=size

On Solaris, sets the maximum size (in bytes) for large pages used for Java heap. The size argument must be a power of 2 (2, 4, 8, 16, ...). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, 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.

The following example illustrates 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 New I/O (the java.nio package) direct-buffer allocations. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, 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:NativeMemoryTracking=mode

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

off: Do not track JVM native memory usage. This is the default behavior if you do not specify the -XX:NativeMemoryTracking option.
summary: Only track memory usage 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 two, 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 will also increase. As a result, you may not realize any benefits from using compressed pointers with large Java heap sizes.

-XX:>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.

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):

-XX:

The preceding example assumes that the path to the userdump.exe utility is specified in the PATH environment variable.

-XX:>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:+PerfDataSaveToFile

If enabled, saves jstat(1) 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 you ran. Use jstat 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 are not printed.

-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 is not printed.

-XX:+RelaxAccessControlCheck

Decreases the amount of access control checks in the verifier. By default, this option is disabled, and it is 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 (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

-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.

-XX:+ShowMessageBoxOnError

Enables displaying 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:

compress={true|false}

Specifies whether to compress the JFR recording log file (of type JFR) on the disk using the gzip file compression utility. This parameter is valid only if the filename parameter is specified. By default it is set to false (recording is not compressed). To enable compression, set the parameter to true.

defaultrecording={true|false}

Specifies whether the recording is a continuous background recording or if it runs for a limited time. By default, this parameter is set to false (recording runs for a limited time). To make the recording run continuously, set the parameter to true.

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 is no delay, and this parameter is set to 0.

dumponexit={true|false}

The dump file is written to the location defined by the filename parameter.

Example:

-XX:StartFlightRecording=name=test,filename=D:\test.jfr,dumponexit=true

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 is not limited, and this parameter is set to 0.

filename=path

Specifies the path and name of the JFR recording log file.

name=identifier

Specifies the identifier for the JFR recording. By default, it is set to Recording x.

maxage=time

maxsize=size

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. For example, to save the recording to test.jfr in the current working directory, and instruct JFR to compress the log file, specify the following:

-XX:StartFlightRecording=filename=test.jfr,compress=true

-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 virtual memory.

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

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

This option is equivalent to -Xss.

-XX:+TraceClassLoading

Enables tracing of classes as they are loaded. By default, this option is disabled and classes are not traced.

-XX:+TraceClassLoadingPreorder

Enables tracing of all loaded classes in the order in which they are referenced. By default, this option is disabled and classes are not traced.

-XX:+TraceClassResolution

Enables tracing of constant pool resolutions. By default, this option is disabled and constant pool resolutions are not traced.

-XX:+TraceClassUnloading

Enables tracing of classes as they are unloaded. By default, this option is disabled and classes are not traced.

-XX:+TraceLoaderConstraints

Enables tracing of the loader constraints recording. By default, this option is disabled and loader constraints recording is not traced.

-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 on the Java SE Products page at http://www.oracle.com/technetwork/java/javase/terms/products/index.html

By default, this option is disabled and the JVM runs without the commercial features. Once they were enabled for a JVM process, it is not possible to disable their use for that process.

If this option is not provided, commercial features can still be unlocked in a running JVM by using the appropriate jcmd diagnostic commands.

-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 .

-XX:-UseBiasedLocking

Disables the use of biased locking. Some applications with significant amounts of uncontended synchronization may attain significant speedups with this flag enabled, whereas applications with certain patterns of locking may see slowdowns. For more information about the biased locking technique, see the example in Java Tuning White Paper at http://www.oracle.com/technetwork/java/tuning-139912.html#section4.2.5

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 less than 32 GB. This option works only for 64-bit JVMs.

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

-XX:+UseLargePages

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

For more information, 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 is enabled. (It is recommended that you do not 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:+AllowUserSignalHandlers

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

Advanced JIT Compiler Options

These 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, which are expected to become default in upcoming releases. By default, this option is disabled and experimental performance features are not 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