(octave.info)Passing parameters to the JVM

---

Next: Java Interface Functions Prev: How to use Java from within Octave Up: Java Interface

---

Enter node , (file) or (file)node

A.4.3 Passing parameters to the JVM
-----------------------------------

In order to execute Java code Octave creates a Java Virtual Machine
(JVM). Such a JVM allocates a fixed amount of initial memory and may
expand this pool up to a fixed maximum memory limit.  The default values
depend on the Java version (Note: javamem.).  The memory
pool is shared by all Java objects running in the JVM.  This strict
memory limit is intended mainly to avoid runaway applications inside web
browsers or in enterprise servers which can consume all memory and crash
the system.  When the maximum memory limit is hit, Java code will throw
exceptions so that applications will fail or behave unexpectedly.

   You can specify options for the creation of the JVM inside a file
named ‘java.opts’.  This is a text file where enter you enter lines
containing ‘-X’ and ‘-D’ options that are then passed to the JVM during
initialization.

   The directory where the Java options file is located is specified by
the environment variable ‘OCTAVE_JAVA_DIR’.  If unset the directory
where ‘javaclasspath.m’ resides is used instead (typically
‘OCTAVE_HOME/share/octave/OCTAVE_VERSION/m/java/’).  You can find this
directory by executing

     which javaclasspath

   The ‘-X’ options allow you to increase the maximum amount of memory
available to the JVM.  The following example allows up to 256 Megabytes
to be used by adding the following line to the ‘java.opts’ file:

     -Xmx256m

   The maximum possible amount of memory depends on your system.  On a
Windows system with 2 Gigabytes main memory you should be able to set
this maximum to about 1 Gigabyte.

   If your application requires a large amount of memory from the
beginning, you can also specify the initial amount of memory allocated
to the JVM.  Adding the following line to the ‘java.opts’ file starts
the JVM with 64 Megabytes of initial memory:

     -Xms64m

   For more details on the available ‘-X’ options of your Java Virtual
Machine issue the command ‘java -X’ at the operating system command
prompt and consult the Java documentation.

   The ‘-D’ options can be used to define system properties which can
then be used by Java classes inside Octave.  System properties can be
retrieved by using the ‘getProperty()’ methods of the ‘java.lang.System’
class.  The following example line defines the property MYPROPERTY and
assigns it the string ‘12.34’.

     -DMyProperty=12.34

   The value of this property can then be retrieved as a string by a
Java object or in Octave:

     octave> javaMethod ("getProperty", "java.lang.System", "MyProperty");
     ans = 12.34

See also: javamem.