Options may be in any order.
For a discussion of
parameters 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 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.
OPTIONS
The launcher has a set of standard options that are supported on
the current runtime environment and will be supported 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However, options below that are described as having been
replaced by another one are obsolete and may be removed in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 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
-client
Selects the Java HotSpot Client
VM.
This is the default.
-server
Selects the Java HotSpot Server
VM.
-classpath classpath
-cp classpath
Specifies 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,
the
-classpath
or
-cp
options only specify the
class path for user classes.
Used with
oldjava,
-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 (.).
-debug
This has been replaced by
-Xdebug.
-Dproperty=value
Sets a system property value.
-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 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.
-noclassgc
This has been replaced by
-Xnoclassgc.
-msn
This has been replaced by
-Xmsn.
-mxn
This has been replaced by
-Xmxn.
-ssn
This has been replaced by
-Xssn.
-verbose
-verbose:class
Displays information about each class loaded.
-verbosegc
This has been replaced by
-verbose:gc.
-verbose:gc
Reports on each garbage collection event.
-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 continues.
-?
-help
Displays usage information and exit.
-X
Displays information about non-standard options and exit.
Non-Standard Options
-Xint
Operates 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.
-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.
-Xdebug
Starts with the debugger enabled.
-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 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
Disables class garbage collection
-Xmsn
Specifies the initial size of the memory 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 megabytes.
The default value is 2m.
-Xmxn
Specifies the maximum size of the memory 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 megabytes.
The default value is 64m.
-Xprof
Profiles the running program, and sends profiling
data to standard output.
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 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.
-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 signals by Java virtual machine (JVM).
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 SIGQUIT to perform thread dumps.
Applications that embed the JVM frequently need to trap signals like
SIGINT or SIGTERM, and in such cases there is the possibility of
interference 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 shutdown-hooks feature. When
-Xrs
is used, the signal masks
for SIGINT, SIGTERM, SIGHUP, and SIGQUIT are not changed by the JVM,
and signal handlers for these signals are not installed.
ENVIRONMENT VARIABLES
CLASSPATH
Used to provide the system with a path to user-defined classes.
Directories are separated by colons.
For example:
