java [ options ] class [ argument ... ]
java [ options ] -jar file.jar [ argument ... ]
options- Command-line options.
class- Name of the class to be invoked.
file.jar- Name of the jar file to be invoked. Used only with
-jar.argument- Argument passed to the main function.
The java tool launches a Java application. It does this by starting a Java runtime environment, loading a specified class, and invoking that class's main method. The method declaration must look like the following:public static void main(String args[])The method must be declared public and static, it must not return any value, and it must accept a String array as a parameter. 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 options that are subject to change in future releases.
- -client
- Select the Java HotSpot Client VM. This is the default.
- -server
- Select the Java HotSpot Server VM.
- -classpath classpath
- -cp classpath
- Specify a list of directories, JAR archives, and ZIP archives to search for class files. Class path entries are separated by colons (:). Specifying -classpath or -cp overrides any setting of the CLASSPATH environment variable.
If -classpath and -cp are not used and CLASSPATH is not set, the user class path consists of the current directory (
.).For more information on class paths, see Setting the Class Path.
- -Dproperty=value
- Set a system property value.
- -jar
- Execute a program encapsulated in a JAR file. The first argument is the name of a JAR file instead of a startup class name. In order for this option to work, the manifest of the JAR file must contain a line of the form Main-Class: classname. Here, classname identifies the class having the public static void main(String[] args) method that serves as your application's starting point. See the Jar tool reference page and the Jar trail of the Java Tutorial for information about working with Jar files and Jar-file manifests.
When you use this option, the JAR file is the source of all user classes, and other user class path settings are ignored.
- -verbose
- -verbose:class
- Display information about each class loaded.
- -verbose:gc
- Report on each garbage collection event.
- -verbose:jni
- Report information about use of native methods and other Java Native Interface activity.
- -version
- Display version information and exit.
- -showversion
- Display version information and continue.
- -?
- -help
- Display usage information and exit.
- -X
- Display information about non-standard options and exit.
- -Xint
- Operate in interpreted-only mode. Compilation to native code is disabled, and all bytecodes are executed by the interpreter. The performance benefits offered by the Java HotSpot VMs' adaptive compiler will not be present in this mode.
- -Xdebug
- Start with the debugger enabled. The Java interpereter prints out a password for jdb's use. Refer to jdb description for more details and an example.
- -Xbootclasspath:bootclasspath
- Specify a colon-separated list of directories, JAR archives, and ZIP archives to search for boot class files. These are used in place of the boot class files included in the Java 2 SDK. Note: Applications that use this option for the purpose of overriding a class in rt.jar should not be deployed as doing so would contravene the Java 2 Runtime Environment binary code license.
- -Xbootclasspath/a:path
- Specify a colon-separated path of directires, JAR archives, and ZIP archives to append to the default bootstrap class path.
- -Xbootclasspath/p:path
- Specify a colon-separated path of directires, JAR archives, and ZIP archives to prepend in front of the default bootstrap class path. Note: Applications that use this option for the purpose of overriding a class in rt.jar should not be deployed as doing so would contravene the Java 2 Runtime Environment binary code license.
- -Xfuture
- Perform strict class-file format checks. For purposes of backwards compatibility, the default format checks performed by the Java 2 SDK's virtual machine are no stricter than the checks performed by 1.1.x versions of the JDK software. The -Xfuture flag turns on stricter class-file format checks that enforce closer conformance to the class-file format specification. Developers are encouraged to use this flag when developing new code because the stricter checks will become the default in future releases of the Java application launcher.
- -Xnoclassgc
- Disable class garbage collection.
- -Xincgc
- Enable the incremental garbage collector. The incremental garbage collector, which is off by default, will eliminate occasional garbage-collection pauses during program execution. However, it can lead to a roughly 10% decrease in overall GC performance.