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java



SYNOPSIS

       java [ options ] class [ argument ...  ]

       java [ options ] -jar file.jar
            [ argument ...  ]


PARAMETERS

       Options  may be in any order.  For a discussion of parame­
       ters which apply to a specific option, see OPTIONS  below.

       options        Command-line options.  See OPTIONS below.

       class          Name of the class to be invoked.

       file.jar       Name  of  the jar file to be invoked.  Used
                      only with the -jar option.


DESCRIPTION

       The java utility 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 have the following signature:

          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 speci­
       fied, the first non-option argument is the name of  a  JAR
       archive containing class and resource files for the appli­
       cation, 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.


OPTIONS

       The  launcher  has a set of standard options that are sup­
       ported on the current runtime environment and will be sup­
       ported  in  future  releases.  However, options below that
       are described as having been replaced by another  one  are
       obsolete and may be removed in a future release.  An addi­
       tional 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.
                           variable.

                           If -classpath and -cp are not used and
                           CLASSPATH  is  not set, the user class
                           path consists of the current directory
                           (.).

       -debug              This has been replaced by -Xdebug.

       -Dproperty=value    Sets a system property value.

       -enableassertions :<package name>... |:<class name>
       -ea :<package name>... |:<class name>
                           Enable assertions. Assertions are dis­
                           abled by default.

                           With no arguments, enableassertions or
                           -ea  enable assertions. With one argu­
                           ment  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 direc­
                           tory. With one argument not ending  in
                           "...",  the  switch enables assertions
                           in the specified class.

                           If a single command line contains mul­
                           tiple  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   packagecom.wom­
                           bat.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.
                           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.wom­
                           bat.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 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 sys­
                           tem classes. A separate switch is pro­
                           vided  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                Executes a program encapsulated  in  a
                           JAR  archive.   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  infor­
                           mation  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

       -verbose:jni        Reports  information  about   use   of
                           native  methods  and other Java Native
                           Interface activity.

       -version            Displays version information and exit.

       -showversion        Displays  version information and con­
                           tinues.

       -?
       -help               Displays usage information and exit.

       -X                  Displays information  about  non-stan­
                           dard options and exit.

   Non-Standard Options
       -Xint               Operates   in  interpreted-only  mode.
                           Compilation to  native  code  is  dis­
                           abled,  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.

       -Xbootclasspath:bootclasspath
                           Specifies  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 and Java 2 Runtime  Environment.

       -Xbootclasspath/a:path
                           Specifies  a  colon-separated  path of
                           directories,  JAR  archives,  and  ZIP
                           archives  to  append  to  the  default
                           bootstrap class path.

       -Xbootclasspath/p:path
                           Specifies a  colon-separated  path  of
                           directories,  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

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

       -Xfuture            Performs  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 for­
                           mat checks that enforce closer confor­
                           mance  to the class-file format speci­
                           fication.  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         Disables class garbage collection

       -Xincgc             Enable the incremental garbage collec­
                           tor.  The  incremental garbage collec­
                           tor, which is  off  by  default,  will
                           eliminate  occasional  garbage-collec­
                           tion pauses during program  execution.
                           However,  it can lead to a roughly 10%
                           decrease in overall GC performance.

       -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 con­
                           tinue  on  the  truncated  file.  This
                           option overrides -verbose:gc  if  both
                           are given on the command line.

       -Xmsn               Specifies the initial size of the mem­
                           ory allocation pool.  This value  must
                           be  greater  than 1000.  To modify the
                           meaning of n, append either the letter
                           k  for  kilobytes  or the letter m for
                           sends profiling data to standard  out­
                           put.   This  option  is  provided as a
                           utility  that  is  useful  in  program
                           development  and is not intended to be
                           be used in production systems.

       -Xrunhprof[:help][:suboption=value,...]
                           Enables cpu, heap, or monitor  profil­
                           ing.   This  option  is typically fol­
                           lowed by  a  list  of  comma-separated
                           suboption=value  pairs.   Run the com­
                           mand java -Xrunhprof:help to obtain  a
                           list  of  suboptions and their default
                           values.

       -Xssn               Each Java thread has two  stacks:  one
                           for Java code and one for C code.  The
                           -Xss option  sets  the  maximum  stack
                           size  that  can be used by C code in a
                           thread to n.   Every  thread  that  is
                           spawned  during  the  execution of the
                           program passed to java has n as its  C
                           stack  size.   The default units for n
                           are bytes and n must be > 1000  bytes.

                           To  modify  the  meaning  of n, append
                           either the letter k for  kilobytes  or
                           the   letter  m  for  megabytes.   The
                           default stack size  is  determined  by
                           the  Linux operating system upon which
                           the Java platform is running.

       -Xrs                Reduce usage of operating-system  sig­
                           nals by Java virtual machine (JVM).

                           Sun's JVM catches signals to implement
                           shutdown hooks for abnormal JVM termi­
                           nation.  The  JVM uses SIGHUP, SIGINT,
                           and SIGTERM to initiate the running of
                           shutdown  hooks.  The JVM uses SIGQUIT
                           to perform thread dumps.

                           Applications that embed the  JVM  fre­
                           quently need to trap signals like SIG­
                           INT or  SIGTERM,  and  in  such  cases
                           there  is the possibility of interfer­
                           ence between the applications'  signal
                           handlers  and  the  JVM shutdown-hooks
                           facility.

                           To avoid such interference,  the  -Xrs
                           option can be used to turn off the JVM


SEE ALSO

       javac(1), jdb(1), javac(1), jar(1), set(1)

       See (or search java.sun.com) for the following:

       JDK File Structure @
         http://java.sun.com/j2se/1.4/docs/tooldocs/linux/jdk­
         files.html

       JAR Files @
         http://java.sun.com/docs/books/tutorial/jar/


NOTES

       All the -X options are unstable.  As noted in the  OPTIONS
       section, some of the "standard" options are obsolete.

                           16 Sep 2002                    java(1)
  




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