java, javac, jre, jdb, javah, javap, javadoc,
appletviewer, rmic, rmiregistry, serialver, native2ascii,
jar, javakey - The Java Development Kit tools
java [options] classname <args>
java_g [options] classname <args>
This reference page describes the java command only. The
Java Development Kit (JDK) is part of the Java Virtual
Machine (VM). If the JDK documentation was installed on
your Tru64 UNIX system, you can view documentation on all
of the JDK tools, and other Java reference material, at
the following location:
/usr/share/doclib/java/index.html
The java command invokes an interpreter that executes Java
bytecodes. It executes Java class files created by a Java
compiler, for instance, javac.
Any arguments that appear after classname on the command
line are passed to the main method of the class.
The java command expects the binary representation of the
class to be in a file called classname.class, which is
generated by compiling the corresponding source file with
javac. All Java class files end with the file name extension
adds when the class is compiled. The classname file
must contain a main method defined as follows:
class Aclass {
public static void main(String argv[]){
. . .
} }
java executes the main method and then exits unless main
creates one or more threads. If any threads are created by
main then java doesn't exit until the last thread exits.
Ordinarily, you compile source files with javac then run
the program using java. However, java can be used to compile
and run programs when the -cs option is used. As each
class file is loaded, its modification date is compared to
the modification date of the class source file. If the
source has been modified more recently, it is recompiled
and the new class file is loaded. java repeats this procedure
until all the classes are correctly compiled and
loaded.
The interpreter can determine whether a class is legitimate
through the mechanism of verification. Verification
ensures prior to their execution that class files do not
violate any language constraints.
java_g is a non-optimized version of java suitable for use
with debuggers like jdb.
The classname argument is the name of the class to be executed.
classname must be fully qualified by including its
package in the name, for example:
% java java.lang.String
When you define your own classes, you need to specify
their location. Use CLASSPATH to do this. CLASSPATH consists
of a colon separated list of directories that specifies
the path. For example:
.:/home/xyz/classes
The system always appends the location of the system
classes onto the end of the class path unless you use the
-classpath option to specify a path.
Allows the Java debugger, jdb, to attach itself to this
java session. When -debug is specified on the command
line, java displays a password which must be used when
starting the debugging session. When a compiled class is
loaded, this option causes the modification time of the
class bytecode file to be compared to that of the class
source file. If the source has been modified more
recently, it is recompiled and the new class file is
loaded. Specifies the path java uses to look up classes.
Overrides the default or the CLASSPATH environment variable
if it is set. Directories are separated by colons.
Thus the general format for path is:
.:<your_path>
For example:
.:/home/xyz/classes:/usr/local/java/classes Sets
the maximum size of the memory allocation pool (the
garbage collected heap) to x. The default is 16
megabytes of memory. x must be greater than or
equal to 1000 bytes.
By default, x is measured in bytes. You can specify
x in either kilobytes or megabytes by appending the
letter k for kilobytes or the letter m for
megabytes. Sets the startup size of the memory
allocation pool (the garbage collected heap) to x.
The default is 1 megabyte of memory. x must be >
1000 bytes.
By default, x is measured in bytes. You can specify
x in either kilobytes or megabytes by appending the
letter k for kilobytes or the letter m for
megabytes. Turns off asynchronous garbage collection.
When activated no garbage collection takes
place unless it is explicitly called or the program
runs out of memory. Normally garbage collection
runs as an asynchronous thread in parallel with
other threads. Turns off garbage collection of
Java classes. By default, the Java interpreter
reclaims space for unused Java classes during
garbage collection. Prints the build version
information. Prints a usage message. Each Java
thread has two stacks: one for Java code and one
for C code. The -ss option sets the maximum stack
size that can be used by C code in a thread to x.
Every thread that is spawned during the execution
of the program passed to java has x as its C stack
size. The default units for x are bytes. The value
of x must be greater than or equal to 1000 bytes.
You can modify the meaning of x by appending either
the letter k for kilobytes or the letter m for
megabytes. The default stack size is 128 kilobytes
(-ss 128k). Each Java thread has two stacks: one
for Java code and one for C code. The -oss option
sets the maximum stack size that can be used by
Java code in a thread to x. Every thread that is
spawned during the execution of the program passed
to java has x as its Java stack size. The default
units for x are bytes. The value of x must be
greater than or equal to 1000 bytes.
You can modify the meaning of x by appending either
the letter k for kilobytes or the letter m for
megabytes. The default stack size is 400 kilobytes
(-oss 400k). Prints a trace of the instructions
executed (java_g only). Causes java to print a
message to stdout each time a class file is loaded.
Runs the verifier on all code. Runs the verifier
on all code that is loaded into the system via a
classloader. -verifyremote is the default for the
interpreter. Turns verification off. Causes the
garbage collector to print out messages whenever it
frees memory. Redefines a property value. propertyName
is the name of the property whose value you
want to change and newValue is the value to change
it to. For example, this command line
% java -Dawt.button.color=green ...
sets the value of the property awt.button.color to
"green". java accepts any number of -D options on
the command line.
ENVIRONMENT VARIABLES [Toc] [Back] Used to provide the system a path to user-defined classes.
Directories are separated by colons, for example,
.:/home/xyz/classes:/usr/local/java/classes
If the JDK documentation was installed on your Tru64 UNIX
system, you can view it at the following location:
/usr/share/doclib/java/index.html
java(5)
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