java(1) java(1)
java - Java interpreter
java [ options ] class [ argument ... ]
java [ options ] -jar file.jar
[ argument ... ]
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.
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 signa-
ture:
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.
However, options below that are described as having been replaced by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 vir-
tual 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
-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 cur-
rent 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 disabled by
default.
With no arguments, enableassertions or -ea enable
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
packagecom.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 dis-
ables assertions. With one argument ending in
"...", the switch disables assertions in the speci-
fied 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.wom-
bat.fruitbat.Brickbat, the following command could
be used:
java -ea:com.wombat.fruitbat... -da:com.wom-
bat.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 system
classes. A separate switch is provided to enable
asserts in all system classes; see -disablesys-
temassertions 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 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 -Xms n.
-mxn This has been replaced by -Xmx n.
-ssn This has been replaced by -Xss n.
-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 exe-
cuted 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: Appli-
cations 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.
-Xdebug Starts with the debugger enabled.
-Xcheck:jni Perform additional check for Java Native Interface
functions.
-Xfuture Performs strict class-file format checks. For pur-
poses of backwards compatibility, the default for-
mat 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 -Xfu-
ture 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
-Xincgc Enable the incremental garbage collector. The
incremental garbage collector, 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 addi-
tion 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.
-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. The uppoer limit for this
value will be approximately 4000m on SPARC plat-
forms and 2000m on x86 platforms, minus overhead
amounts.
-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 maxi-
mum 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 let-
ter 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.
CLASSPATH Used to provide the system with a path to user-
defined classes. Directories are separated by
colons. For example:
.:/home/avh/classes:/usr/local/java/classes
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/jdkfiles.html
JAR Files @
http://java.sun.com/docs/books/tutorial/jar/
All the -X options are unstable. As noted in the OPTIONS section, some
of the "standard" options are obsolete.
23 Apr 2001 java(1)