java - the Java application launcher

SYNOPSIS

 
    java [ threads flag ] [ options ] class [ argument ... ]
    java [ threads flag ] [ options ] -jar file.jar [ argument ... ]
    oldjava [ threads flag ] [ options ] class [ 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.

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 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 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.

JAVA AND OLDJAVA
On Solaris systems, the java launcher tool comes in two variations: java, which implements all 1.2 features; and oldjava, a limited-feature launcher tool, which supports programming techniques that are incompatible with some 1.2 features. These are the differences between java and oldjava: This command using oldjava 
oldjava -classpath <path> ...
is equivalent to this command using java 
java -Xbootclasspath:<path> -Djava.ext.dirs= ...
where in both cases <path> contains the file rt.jar. (See the JDK FIle Structure document for a description of rt.jar and its location in the JDK software.)

THE JIT

The default behavior of the launcher is to execute bytecodes using a Just-in-Time compiler, or JIT. The default compiler is located at jre/lib/sparc/libsunwjit.so. When a class is loaded, the JIT translates the class bytecodes into native machine code. Using a JIT causes a slight delay after each class load, but can improve overall program performance. In some cases, execution time will improve by a factor of ten.

If the JIT is disabled, bytecodes are executed directly by an interpreter. There are two ways to disable the JIT:

You can also use JAVA_COMPILER or java.compiler to the specify that an alternative JIT should be used: 
% setenv JAVA_COMPILER foo
or 
% java -Djava.compiler=foo myapp
The letters lib are prepended to "foo" and an .so filename extension is added, so that, in this example, the virtual machine will search for a JIT compiler named libfoo.so. The search for the alternative compiler is made in the jre/lib/sparc directory and or in the path specified by the sun.boot.library.path property, if it is set. Here is an example using of using the sun.boot.library.path property to specify an alternative JIT path (the example assumes a JIT named libfoo.so is located in directory /java): 
java -Dsun.boot.libary.path=/jdk1.2.2/jre/lib/sparc:/java -Djava.compiler=foo MyApp
Note that the 1.2.2 SDK's own jre/lib/sparc path should be included first in the value of the sun.boot.library.path property. If no such compiler is found, the virtual machine will default to using the interpreter.

OPTIONS
The launcher has a set of standard options that are supported on the current runtime environment and will be supported in future releases. An additional set of non-standard options are specific to the current virtual machine implementation and are subject to change in the future. Non-standard options begin with -X

Standard 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 colons (:). Specifying -classpath or -cp overrides any setting of the CLASSPATH environment variable.

Used with java or javaw, -classpath or -cp only specify the class path for user classes. Used with oldjava or oldjavaw, -classpath or -cp specify the class path for both user classes and bootstrap classes.

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.

The oldjava and oldjavaw tools do not support the -jar option.

-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.

-?
-help
Display usage information and exit.

-X
Display information about non-standard options and exit.

Non-Standard Options
-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 JDK 1.2 software.

-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.

-Xnoclassgc
Disable class garbage collection

-Xmsn
Specify the initial size of the memory allocation pool. This value must greather than 1000. To multiply the value by 1000, append the letter k. To multiply the value by 1 million, append the letter m. The default value is 1m

-Xmxn
Specify the maximum size of the memory allocation pool. This value must greather than 1000. To multiply the value by 1000, append the letter k. To multiply the value by 1 million, append the letter m. The default value is 64m.

-Xrunhprof[:help][:<suboption>=<value>,...]
Enables cpu, heap, or monitor profiling. This option is typically followed by a list of comma-separated "<suboption>=<value>" pairs. Run the command java -Xrunhprof:help to obtain a list of suboptions and their default values.

-Xrs
Reduce the use of operating system signals.

-Xcheck:jni
Perform additional check for Java Native Interface functions.

-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.

SEE ALSO