java [ options ] class [ argument ... ]
java [ options ] -jar file.jar [ argument ... ]
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.
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
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:hprof
-agentlib:jdwp=help
-agentlib:hprof=help
For more information, see JVMTI Agent Command Line Options.
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.
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.
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.
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.
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.
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:"1.5.0_04 1.5*&1.5.1_02+"The meaning of the above is that the class or jar file requires either version 1.5.0_02, or a version with 1.5 as a version-id prefix and that is not less than 1.5.1_02. 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.
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.
-Xms6291456
-Xms6144k
-Xms6m
-Xmx83886080
-Xmx81920k
-Xmx80m
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:
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:
"1.5.0_03+"
Would utilize any version greater than 1.5.0_03. This is useful for a case where an interface was introduced (or a bug fixed) in the release specified.
"1.5.0_03+&1.5*"
"1.4.2_05+&1.4* 1.5+"Similar to item 2. this is useful when a change was introduced in a release (1.5) but also made available in updates to previous releases.