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octave: Passing parameters to the JVM

 
 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 (javamem XREFjavamem.).  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.
 

Info Catalog octave: How to use Java from within Octave octave: Java Interface octave: Java Interface Functions