java - the Java application launcher - JDK 5 Documentation v1.5.0, Java 2 SDK 英文文档
java - the Java application launcher
SYNOPSIS
java [ options ] class [ argument ... ]
java [ options ] -jar file.jar [ argument ... ]
javaw [ options ] class [ argument ... ]
javaw [ options ] -jar file.jar [ argument ... ]
DESCRIPTION
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
Stringarray as a para meter. 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 argume nt is the name of a JAR archive containing class and resource f iles 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 javaw command is identical to java, except that with javaw there is 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 for some reason.
OPTIONS
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 default Java HotSpot VMs provide a set of non-standard options that are subject to change in future releases.
Standard Options
- -client
- Select the Java HotSpot Client VM.
For more information, see Server-Class Machine Detection
- -server
- Select the Java HotSpot Server VM.
For more information, see Server-Class Machine Detection
- -agentlib:libname[=options]
- Load native agent library libname, e.g.
-agentlib:hprof
-agentlib:jdwp=help
-agentlib:hprof=help
For more information, see JVMTI Agent Command Line Options.
- -agentpath:pathname[=options]
- Load a native agent library by full pathname. For more information, see JVMTI Agent Command Line Options.
- -classpath classpath
- -cp classpath
- Specify a list of directories, JAR archives, and ZIP archives to search for class files. Class path entries are separated by semicolons (;). 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. If value is a string that contains spaces, you must enclose the string in double quotes:
java -Dfoo="some string" SomeClass- -enableassertions[:<package name>"..." | :<class name> ]
- -ea[:<package name>"..." | :<class name> ]
- Enable assertions. Assertions are disabled by default.
With no arguments, enableassertions or -ea enables assertions. With one argument ending in "...", the switch enables assertions in the specified package and any subpackages. If the argument is simply "...", the switch enables assertions in the unnamed package in the current working directory. With one argument not ending in "...", the switch enables assertions in the specified class.
If a single command line contains multiple instances of these switches, they are processed in order before loading any classes. So, for example, to run a program with assertions enabled only in package com.wombat.fruitbat (and any subpackages), the following command could be used:
java -ea:com.wombat.fruitbat... <Main Class>The -enableassertions and -ea switches apply to all s 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.
- -disableassertions[:<package name>"..." | :<class ; ]
- -da[:<package name>"..." | :<class name> ]
- Disable assertions. This is the default.
With no arguments, disableassertions or -da disables assertions. With one argument ending in "...", the switch disables assertions in the specified package and any subpackages. If the argument is simply "...", the switch disables assertions in the unnamed package in the rent 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 lt;Main Class>The -disableassertions and -da switches apply to all ss 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.
- -enablesystemassertions
- -esa
- Enable asserts in all system classes (sets the default assertion status for system classes to true).
- -disablesystemassertions
- -dsa
- Disables asserts in all system classes.
- -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.
- -javaagent:jarpath[=options]
- Load a Java programming language agent, see java.lang.instrument.
- -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.
Non-Standard Options
- -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 Client VM's adaptive compiler will not be present in this mode.
- -Xbatch
- Disable background compilation. Normally the VM will compile the method as a background task, running the method in interpreter mode until the background compilation is finished. The -Xbatch flag disables background compilation so that compilation of all methods proceeds as a foreground task until completed.
- -Xdebug
- Start with support for JVMDI enabled. JVMDI has been deprecated and is not used for debugging in J2SE 5.0, so this option isn't needed for debugging in J2SE 5.0.
- -Xbootclasspath:bootclasspath
- Specify a semicolon-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 semicolon-separated path of directires, JAR archives, and ZIP archives to append to the default bootstrap class path.
- -Xbootclasspath/p:path
- Specify a semicolon-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.
- -Xcheck:jni
- Perform additional checks for Java Native Interface (JNI) functions. Specifically, the Java Virtual Machine validates the parameters passed to the JNI function as well as the runtime environment data before processing the JNI request. Any invalid data encountered indicates a problem in the native code, and the Java Virtual Machine will terminate with a fatal error in such cases. Expect a performance degradation when this option is used.
- -Xfuture
- Perform strict class-file format checks. For purposes of backwards compatibility, the default format checks performed by the 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 reduce the occasional long garbage-collection pauses during program execution. The incremental garbage collector will at times execute concurrently with the program and during such times will reduce the processor capacity available to the program.
- -Xloggc:file
- Report on each garbage collection event, as with -verbose:gc, but log this data to file. In addition to the information -verbose:gc gives, each reported event will be preceeded by the time (in seconds) since the first garbage-collection event.
Always use a local file system for storage of this file to avoid stalling the JVM due to network latency. The file may be truncated in the case of a full file system and logging will continue on the truncated file. This option overrides -verbose:gc if both are given on the command line.
SEE ALSO
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