@c DO NOT EDIT!  Generated automatically by munge-texi.pl.

@c Copyright (C) 2010-2015 Martin Hepperle
@c
@c This file is part of Octave.
@c
@c Octave is free software; you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by the
@c Free Software Foundation; either version 3 of the License, or (at
@c your option) any later version.
@c
@c Octave is distributed in the hope that it will be useful, but WITHOUT
@c ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
@c FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
@c for more details.
@c
@c You should have received a copy of the GNU General Public License
@c along with Octave; see the file COPYING.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Java Interface
@chapter Java Interface

@cindex using Octave with Java
@cindex Java, using with Octave
@cindex calling Java from Octave
@cindex Java, calling from Octave
@cindex calling Octave from Java
@cindex Octave, calling from Java

The Java Interface is designed for calling Java functions from within Octave.
If you want to do the reverse, and call Octave from within Java, try
a library like
@code{javaOctave} (@url{http://kenai.com/projects/javaOctave}) or
@code{joPas} (@url{http://jopas.sourceforge.net}).

@menu
* Java Interface Functions::
* Dialog Box Functions::
* FAQ - Frequently asked Questions::
@end menu

@node Java Interface Functions
@section Java Interface Functions

The following functions are the core of the Java Interface.  They provide
a way to create a Java object, get and set its data fields, and call Java
methods which return results to Octave.

@cindex object, creating a Java object
@c javaObject libinterp/octave-value/ov-java.cc
@anchor{XREFjavaObject}
@deftypefn  {Built-in Function} {@var{jobj} =} javaObject (@var{classname})
@deftypefnx {Built-in Function} {@var{jobj} =} javaObject (@var{classname}, @var{arg1}, @dots{})
Create a Java object of class @var{classsname}, by calling the class
constructor with the arguments @var{arg1}, @dots{}

The first example below creates an uninitialized object,
while the second example supplies an initial argument to the constructor.

@example
@group
x = javaObject ("java.lang.StringBuffer")
x = javaObject ("java.lang.StringBuffer", "Initial string")
@end group
@end example

@seealso{@ref{XREFjavaMethod,,javaMethod}, @ref{XREFjavaArray,,javaArray}}
@end deftypefn


@cindex array, creating a Java array
@c javaArray scripts/java/javaArray.m
@anchor{XREFjavaArray}
@deftypefn  {Function File} {@var{jary} =} javaArray (@var{classname}, @var{sz})
@deftypefnx {Function File} {@var{jary} =} javaArray (@var{classname}, @var{m}, @var{n}, @dots{})

Create a Java array of size @var{sz} with elements of class
@var{classname}.  @var{classname} may be a Java object representing a class
or a string containing the fully qualified class name.  The size of
the object may also be specified with individual integer arguments
@var{m}, @var{n}, etc.

The generated array is uninitialized.  All elements are set to null
if @var{classname} is a reference type, or to a default value (usually 0)
if @var{classname} is a primitive type.

Sample code:

@example
@group
jary = javaArray ("java.lang.String", 2, 2);
jary(1,1) = "Hello";
@end group
@end example
@seealso{@ref{XREFjavaObject,,javaObject}}
@end deftypefn


There are many different variable types in Octave but only ones created through
@code{javaObject} can use Java functions.  Before using Java with an unknown
object the type can be checked with @code{isjava}.

@c isjava libinterp/octave-value/ov-java.cc
@anchor{XREFisjava}
@deftypefn {Built-in Function} {} isjava (@var{x})
Return true if @var{x} is a Java object.
@seealso{@ref{XREFclass,,class}, @ref{XREFtypeinfo,,typeinfo}, @ref{XREFisa,,isa}, @ref{XREFjavaObject,,javaObject}}
@end deftypefn


Once an object has been created it is natural to find out what fields the
object has and to read (get) and write (set) them.

@cindex fields, displaying available fields of a Java object
In Octave the @code{fieldnames} function for structures has been overloaded
to return the fields of a Java object.  For example:

@example
@group
dobj = javaObject ("java.lang.Double", pi);
fieldnames (dobj)
@result{}
@{
  [1,1] = public static final double java.lang.Double.POSITIVE_INFINITY
  [1,2] = public static final double java.lang.Double.NEGATIVE_INFINITY
  [1,3] = public static final double java.lang.Double.NaN
  [1,4] = public static final double java.lang.Double.MAX_VALUE
  [1,5] = public static final double java.lang.Double.MIN_NORMAL
  [1,6] = public static final double java.lang.Double.MIN_VALUE
  [1,7] = public static final int java.lang.Double.MAX_EXPONENT
  [1,8] = public static final int java.lang.Double.MIN_EXPONENT
  [1,9] = public static final int java.lang.Double.SIZE
  [1,10] = public static final java.lang.Class java.lang.Double.TYPE
@}
@end group
@end example

@cindex field, returning value of Java object field
The analogy of objects with structures is carried over into reading and
writing object fields.  To read a field the object is indexed with the
@samp{.} operator from structures.  This is the preferred method for reading
fields, but Octave also provides a function interface to read fields with
@code{java_get}.  An example of both styles is shown below.

@example
@group
dobj = javaObject ("java.lang.Double", pi);
dobj.MAX_VALUE
@result{}  1.7977e+308
java_get ("java.lang.Float", "MAX_VALUE")
@result{}  3.4028e+38
@end group
@end example

@c java_get scripts/java/java_get.m
@anchor{XREFjava_get}
@deftypefn {Function File} {@var{val} =} java_get (@var{obj}, @var{name})
Get the value of the field @var{name} of the Java object @var{obj}.  For
static fields, @var{obj} can be a string representing the fully qualified
name of the corresponding class.

When @var{obj} is a regular Java object, structure-like indexing can be
used as a shortcut syntax.  For instance, the two following statements are
equivalent

@example
@group
  java_get (x, "field1")
  x.field1
@end group
@end example

@seealso{@ref{XREFjava_set,,java_set}, @ref{XREFjavaMethod,,javaMethod}, @ref{XREFjavaObject,,javaObject}}
@end deftypefn


@cindex field, setting value of Java object field
@c java_set scripts/java/java_set.m
@anchor{XREFjava_set}
@deftypefn {Function File} {@var{obj} =} java_set (@var{obj}, @var{name}, @var{val})
Set the value of the field @var{name} of the Java object @var{obj} to
@var{val}.  For static fields, @var{obj} can be a string representing the
fully qualified named of the corresponding Java class.

When @var{obj} is a regular Java object, structure-like indexing can be
used as a shortcut syntax.  For instance, the two following statements are
equivalent

@example
@group
  java_set (x, "field1", val)
  x.field1 = val
@end group
@end example

@seealso{@ref{XREFjava_get,,java_get}, @ref{XREFjavaMethod,,javaMethod}, @ref{XREFjavaObject,,javaObject}}
@end deftypefn


@cindex methods, displaying available methods of a Java object
To see what functions can be called with an object use @code{methods}.
For example, using the previously created @var{dobj}:

@example
@group
methods (dobj)
@result{}
Methods for class java.lang.Double:
boolean equals(java.lang.Object)
java.lang.String toString(double)
java.lang.String toString()
@dots{}
@end group
@end example

To call a method of an object the same structure indexing operator @samp{.}
is used.  Octave also provides a functional interface to calling the methods
of an object through @code{javaMethod}.  An example showing both styles is
shown below.

@example
@group
dobj = javaObject ("java.lang.Double", pi);
dobj.equals (3)
@result{}  0
javaMethod ("equals", dobj, pi)
@result{}  1
@end group
@end example

@cindex method, invoking a method of a Java object
@c javaMethod libinterp/octave-value/ov-java.cc
@anchor{XREFjavaMethod}
@deftypefn  {Built-in Function} {@var{ret} =} javaMethod (@var{methodname}, @var{obj})
@deftypefnx {Built-in Function} {@var{ret} =} javaMethod (@var{methodname}, @var{obj}, @var{arg1}, @dots{})
Invoke the method @var{methodname} on the Java object @var{obj} with the
arguments @var{arg1}, @dots{}  For static methods, @var{obj} can be a string
representing the fully qualified name of the corresponding class.  The
function returns the result of the method invocation.

When @var{obj} is a regular Java object, structure-like indexing can be
used as a shortcut syntax.  For instance, the two following statements are
equivalent

@example
@group
  ret = javaMethod ("method1", x, 1.0, "a string")
  ret = x.method1 (1.0, "a string")
@end group
@end example

@seealso{@ref{XREFmethods,,methods}, @ref{XREFjavaObject,,javaObject}}
@end deftypefn


The following three functions are used to display and modify the
class path used by the Java Virtual Machine.  This is entirely separate
from Octave's PATH variable and is used by the JVM to find the correct
code to execute.

@cindex classpath, displaying
@cindex classpath, dynamic
@cindex dynamic classpath
@cindex classpath, static
@cindex static classpath
@c javaclasspath scripts/java/javaclasspath.m
@anchor{XREFjavaclasspath}
@deftypefn  {Function File} {} javaclasspath ()
@deftypefnx {Function File} {@var{dpath} =} javaclasspath ()
@deftypefnx {Function File} {[@var{dpath}, @var{spath}] =} javaclasspath ()
@deftypefnx {Function File} {@var{clspath} =} javaclasspath (@var{what})
Return the class path of the Java virtual machine in the form of a cell
array of strings.

If called with no inputs:

@itemize
@item If no output is requested, the dynamic and static classpaths are
printed to the standard output.

@item If one output value @var{dpath} is requested, the result is
the dynamic classpath.

@item If two output values@var{dpath} and @var{spath} are
requested, the first variable will contain the dynamic classpath and
the second will be contain the static classpath.
@end itemize

If called with a single input parameter @var{what}:

@table @asis
@item @qcode{"-dynamic"}
Return the dynamic classpath.

@item @qcode{"-static"}
Return the static classpath.

@item @qcode{"-all"}
Return both the static and dynamic classpath in a single cellstr.
@end table
@seealso{@ref{XREFjavaaddpath,,javaaddpath}, @ref{XREFjavarmpath,,javarmpath}}
@end deftypefn


@findex javaaddpath
@cindex classpath, adding new path
@cindex path, adding to classpath
@cindex classpath, dynamic
@cindex dynamic classpath, adding new path
@c javaaddpath scripts/java/javaaddpath.m
@anchor{XREFjavaaddpath}
@deftypefn  {Function File} {} javaaddpath (@var{clspath})
@deftypefnx {Function File} {} javaaddpath (@var{clspath1}, @dots{})
Add @var{clspath} to the dynamic class path of the Java virtual
machine.  @var{clspath} may either be a directory where @file{.class}
files are found, or a @file{.jar} file containing Java classes.
Multiple paths may be added at once by specifying additional arguments.
@seealso{@ref{XREFjavarmpath,,javarmpath}, @ref{XREFjavaclasspath,,javaclasspath}}
@end deftypefn


@cindex classpath, removing path
@cindex path, removing from classpath
@c javarmpath scripts/java/javarmpath.m
@anchor{XREFjavarmpath}
@deftypefn  {Function File} {} javarmpath (@var{clspath})
@deftypefnx {Function File} {} javarmpath (@var{clspath1}, @dots{})
Remove @var{clspath} from the dynamic class path of the Java virtual
machine.  @var{clspath} may either be a directory where @file{.class}
files are found, or a @file{.jar} file containing Java classes.
Multiple paths may be removed at once by specifying additional arguments.
@seealso{@ref{XREFjavaaddpath,,javaaddpath}, @ref{XREFjavaclasspath,,javaclasspath}}
@end deftypefn


The following functions provide information and control over the interface
between Octave and the Java Virtual Machine.

@c javachk scripts/java/javachk.m
@anchor{XREFjavachk}
@deftypefn  {Function File} {} javachk (@var{feature})
@deftypefnx {Function File} {} javachk (@var{feature}, @var{component})
@deftypefnx {Function File} {@var{msg} =} javachk (@dots{})
Check for the presence of the Java @var{feature} in the current session
and print or return an error message if it is not.

Possible features are:

@table @asis
@item @qcode{"awt"}
Abstract Window Toolkit for GUIs.

@item @qcode{"desktop"}
Interactive desktop is running.

@item @qcode{"jvm"}
Java Virtual Machine.

@item @qcode{"swing"}
Swing components for lightweight GUIs.
@end table

If @var{feature} is supported and:

@itemize @bullet
@item
No output argument is requested:

Return an empty string

@item
An output argument is requested:

Return a struct with fields @qcode{"feature"} and @qcode{"identifier"}
both empty

@end itemize

If @var{feature} is not supported and:

@itemize @bullet
@item
No output argument is requested:

Emit an error message.

@item
An output argument is requested:

Return a struct with field @qcode{"feature"} set to @var{feature} and
field @qcode{"identifier"} set to @var{component}

@end itemize

The optional input @var{component} will be used in place of @var{feature}
in any error messages for greater specificity.

@code{javachk} determines if specific Java features are available in an
Octave session.  This function is provided for scripts which may alter
their behavior based on the availability of Java.  The feature
@qcode{"desktop"} is never available as Octave has no Java-based desktop.
Other features may be available if Octave was compiled with the Java
Interface and Java is installed.

@seealso{@ref{XREFerror,,error}, @ref{XREFusejava,,usejava}}
@end deftypefn


@c usejava scripts/java/usejava.m
@anchor{XREFusejava}
@deftypefn {Function File} {} usejava (@var{feature})
Return true if the Java element @var{feature} is available.

Possible features are:

@table @asis
@item @qcode{"awt"}
Abstract Window Toolkit for GUIs.

@item @qcode{"desktop"}
Interactive desktop is running.

@item @qcode{"jvm"}
Java Virtual Machine.

@item @qcode{"swing"}
Swing components for lightweight GUIs.
@end table

@code{usejava} determines if specific Java features are available in an
Octave session.  This function is provided for scripts which may alter
their behavior based on the availability of Java.  The feature
@qcode{"desktop"} always returns @code{false} as Octave has no Java-based
desktop.  Other features may be available if Octave was compiled with the
Java Interface and Java is installed.
@seealso{@ref{XREFjavachk,,javachk}}
@end deftypefn


@cindex memory, displaying Java memory status
@c javamem scripts/java/javamem.m
@anchor{XREFjavamem}
@deftypefn  {Function File} {} javamem ()
@deftypefnx {Function File} {@var{jmem} =} javamem ()
Show the current memory usage of the Java virtual machine (JVM)
and run the garbage collector.

When no return argument is given the info is printed to the screen.
Otherwise, the output cell array @var{jmem} contains Maximum, Total,
and Free memory (in bytes).

All Java-based routines are run in the JVM's shared memory pool,
a dedicated and separate part of memory claimed by the JVM from
your computer's total memory (which comprises physical RAM and
virtual memory / swap space on hard disk).

The maximum allowable memory usage can be configured using the file
@file{java.opts}.  The directory where this file resides is
determined by the environment variable @w{@env{OCTAVE_JAVA_DIR}}.
If unset, the directory where @file{javaaddpath.m} resides is used instead
(typically
@file{@w{@env{OCTAVE_HOME}}/share/octave/@w{@env{OCTAVE_VERSION}}/m/java/}).

@file{java.opts} is a plain text file with one option per line.  The
default initial memory size and default maximum memory size (which
are both system dependent) can be overridden like so:

@nospell{-Xms64m}

@nospell{-Xmx512m}

(in megabytes in this example).
You can adapt these values to your own requirements if your system
has limited available physical memory or if you get Java memory
errors.

"Total memory" is what the operating system has currently assigned
to the JVM and depends on actual and active memory usage.
"Free memory" is self-explanatory.  During operation of Java-based
Octave functions the amount of Total and Free memory will vary,
due to Java's own cleaning up and your operating system's memory
management.
@end deftypefn


@c java_matrix_autoconversion libinterp/octave-value/ov-java.cc
@anchor{XREFjava_matrix_autoconversion}
@deftypefn  {Built-in Function} {@var{val} =} java_matrix_autoconversion ()
@deftypefnx {Built-in Function} {@var{old_val} =} java_matrix_autoconversion (@var{new_val})
@deftypefnx {Built-in Function} {} java_matrix_autoconversion (@var{new_val}, "local")
Query or set the internal variable that controls whether Java arrays are
automatically converted to Octave matrices.  The default value is false.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.  
The original variable value is restored when exiting the function.
@seealso{@ref{XREFjava_unsigned_autoconversion,,java_unsigned_autoconversion}, @ref{XREFdebug_java,,debug_java}}
@end deftypefn


@c java_unsigned_autoconversion libinterp/octave-value/ov-java.cc
@anchor{XREFjava_unsigned_autoconversion}
@deftypefn  {Built-in Function} {@var{val} =} java_unsigned_autoconversion ()
@deftypefnx {Built-in Function} {@var{old_val} =} java_unsigned_autoconversion (@var{new_val})
@deftypefnx {Built-in Function} {} java_unsigned_autoconversion (@var{new_val}, "local")
Query or set the internal variable that controls how integer classes are
converted when @code{java_matrix_autoconversion} is enabled.  When enabled,
Java arrays of class Byte or Integer are converted to matrices of class
uint8 or uint32 respectively.  The default value is true.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.  
The original variable value is restored when exiting the function.
@seealso{@ref{XREFjava_matrix_autoconversion,,java_matrix_autoconversion}, @ref{XREFdebug_java,,debug_java}}
@end deftypefn


@c debug_java libinterp/octave-value/ov-java.cc
@anchor{XREFdebug_java}
@deftypefn  {Built-in Function} {@var{val} =} debug_java ()
@deftypefnx {Built-in Function} {@var{old_val} =} debug_java (@var{new_val})
@deftypefnx {Built-in Function} {} debug_java (@var{new_val}, "local")
Query or set the internal variable that determines whether extra debugging
information regarding the initialization of the JVM and any Java exceptions
is printed.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.  
The original variable value is restored when exiting the function.
@seealso{@ref{XREFjava_matrix_autoconversion,,java_matrix_autoconversion}, @ref{XREFjava_unsigned_autoconversion,,java_unsigned_autoconversion}}
@end deftypefn


@node Dialog Box Functions
@section Dialog Box Functions

The following functions all use the Java Interface to provide some form
of dialog box.

@cindex dialog, displaying a warning dialog
@c msgbox scripts/gui/msgbox.m
@anchor{XREFmsgbox}
@deftypefn  {Function File} {@var{h} =} msgbox (@var{msg})
@deftypefnx {Function File} {@var{h} =} msgbox (@var{msg}, @var{title})
@deftypefnx {Function File} {@var{h} =} msgbox (@var{msg}, @var{title}, @var{icon})
Display @var{msg} using a message dialog box.

The message may have multiple lines separated by newline characters
(@qcode{"\n"}), or it may be a cellstr array with one element for each
line.  The optional input @var{title} (character string) can be used to
decorate the dialog caption.

The optional argument @var{icon} selects a dialog icon.
It can be one of @qcode{"none"} (default), @qcode{"error"},
@qcode{"help"}, or @qcode{"warn"}.

The return value is always 1.
@seealso{@ref{XREFerrordlg,,errordlg}, @ref{XREFhelpdlg,,helpdlg}, @ref{XREFinputdlg,,inputdlg}, @ref{XREFlistdlg,,listdlg}, @ref{XREFquestdlg,,questdlg}, @ref{XREFwarndlg,,warndlg}}
@end deftypefn


@cindex dialog, displaying an error dialog
@c errordlg scripts/gui/errordlg.m
@anchor{XREFerrordlg}
@deftypefn  {Function File} {@var{h} =} errordlg (@var{msg})
@deftypefnx {Function File} {@var{h} =} errordlg (@var{msg}, @var{title})
Display @var{msg} using an error dialog box.

The message may have multiple lines separated by newline characters
("\n"), or it may be a cellstr array with one element for each
line.  The optional input @var{title} (character string) can be used to
set the dialog caption.  The default title is @qcode{"Error Dialog"}.

The return value is always 1.
@seealso{@ref{XREFhelpdlg,,helpdlg}, @ref{XREFinputdlg,,inputdlg}, @ref{XREFlistdlg,,listdlg}, @ref{XREFmsgbox,,msgbox}, @ref{XREFquestdlg,,questdlg}, @ref{XREFwarndlg,,warndlg}}
@end deftypefn


@cindex dialog, displaying a help dialog
@c helpdlg scripts/gui/helpdlg.m
@anchor{XREFhelpdlg}
@deftypefn  {Function File} {@var{h} =} helpdlg (@var{msg})
@deftypefnx {Function File} {@var{h} =} helpdlg (@var{msg}, @var{title})
Display @var{msg} in a help dialog box.

The message may have multiple lines separated by newline characters
("\n"), or it may be a cellstr array with one element for each
line.  The optional input @var{title} (character string) can be used to
set the dialog caption.  The default title is @qcode{"Help Dialog"}.

The return value is always 1.
@seealso{@ref{XREFerrordlg,,errordlg}, @ref{XREFinputdlg,,inputdlg}, @ref{XREFlistdlg,,listdlg}, @ref{XREFmsgbox,,msgbox}, @ref{XREFquestdlg,,questdlg}, @ref{XREFwarndlg,,warndlg}}
@end deftypefn


@cindex dialog, displaying an input dialog
@c inputdlg scripts/gui/inputdlg.m
@anchor{XREFinputdlg}
@deftypefn  {Function File} {@var{cstr} =} inputdlg (@var{prompt})
@deftypefnx {Function File} {@var{cstr} =} inputdlg (@var{prompt}, @var{title})
@deftypefnx {Function File} {@var{cstr} =} inputdlg (@var{prompt}, @var{title}, @var{rowscols})
@deftypefnx {Function File} {@var{cstr} =} inputdlg (@var{prompt}, @var{title}, @var{rowscols}, @var{defaults})
Return user input from a multi-textfield dialog box in a cell array
of strings, or an empty cell array if the dialog is closed by the
Cancel button.

Inputs:

@table @var
@item prompt
A cell array with strings labeling each text field.  This input is required.

@item title
String to use for the caption of the dialog.  The default is @qcode{"Input
Dialog"}.

@item rowscols
Specifies the size of the text fields and can take three forms:

@enumerate
@item a scalar value which defines the number of rows used for each
text field.

@item a vector which defines the individual number of rows
used for each text field.

@item a matrix which defines the individual number of rows and
columns used for each text field.  In the matrix each row describes
a single text field.  The first column specifies the number of input
rows to use and the second column specifies the text field width.
@end enumerate

@item defaults
A list of default values to place in each text fields.  It must be
a cell array of strings with the same size as @var{prompt}.
@end table
@seealso{@ref{XREFerrordlg,,errordlg}, @ref{XREFhelpdlg,,helpdlg}, @ref{XREFlistdlg,,listdlg}, @ref{XREFmsgbox,,msgbox}, @ref{XREFquestdlg,,questdlg}, @ref{XREFwarndlg,,warndlg}}
@end deftypefn


@cindex dialog, displaying a list dialog
@c listdlg scripts/gui/listdlg.m
@anchor{XREFlistdlg}
@deftypefn {Function File} {[@var{sel}, @var{ok}] =} listdlg (@var{key}, @var{value}, @dots{})
Return user inputs from a list dialog box in a vector of
selection indices @var{sel} and a flag @var{ok} indicating how the
user closed the dialog box.  The value of @var{ok} is 1 if the user
closed the box with the OK button, otherwise it is 0 and @var{sel} is
empty.

The indices in @var{sel} are 1-based.

The arguments are specified in form of @var{key}, @var{value} pairs.
The @qcode{"ListString"} argument pair must be specified.

Valid @var{key} and @var{value} pairs are:

@table @asis
@item @qcode{"ListString"}
a cell array of strings comprising the content of the list.

@item @qcode{"SelectionMode"}
can be either @qcode{"Single"} or @qcode{"Multiple"} (default).

@item @qcode{"ListSize"}
a vector with two elements @var{width} and @var{height} defining
the size of the list field in pixels.  Default is [160 300].

@item @qcode{"InitialValue"}
a vector containing 1-based indices of preselected elements.  Default
is 1 (first item).

@item @qcode{"Name"}
a string to be used as the dialog caption.  Default is "".

@item @qcode{"PromptString"}
a cell array of strings to be displayed above the list field.  Default
is @{@}.

@item @qcode{"OKString"}
a string used to label the OK button.  Default is @qcode{"OK"}.

@item @qcode{"CancelString"}
a string used to label the Cancel button.  Default is @qcode{"Cancel"}.
@end table

Example:

@example
@group
[sel, ok] = listdlg ("ListString", @{"An item", "another", "yet another"@},
                     "SelectionMode", "Multiple");
if (ok == 1)
  for i = 1:numel (sel)
    disp (sel(i));
  endfor
endif
@end group
@end example

@seealso{@ref{XREFmenu,,menu}, @ref{XREFerrordlg,,errordlg}, @ref{XREFhelpdlg,,helpdlg}, @ref{XREFinputdlg,,inputdlg}, @ref{XREFmsgbox,,msgbox}, @ref{XREFquestdlg,,questdlg}, @ref{XREFwarndlg,,warndlg}}
@end deftypefn


@cindex dialog, displaying a question dialog
@c questdlg scripts/gui/questdlg.m
@anchor{XREFquestdlg}
@deftypefn  {Function File} {@var{btn} =} questdlg (@var{msg})
@deftypefnx {Function File} {@var{btn} =} questdlg (@var{msg}, @var{title})
@deftypefnx {Function File} {@var{btn} =} questdlg (@var{msg}, @var{title}, @var{default})
@deftypefnx {Function File} {@var{btn} =} questdlg (@var{msg}, @var{title}, @var{btn1}, @var{btn2}, @var{default})
@deftypefnx {Function File} {@var{btn} =} questdlg (@var{msg}, @var{title}, @var{btn1}, @var{btn2}, @var{btn3}, @var{default})
Display @var{msg} using a question dialog box and return the caption
of the activated button.

The dialog may contain two or three buttons which will all close the dialog.

The message may have multiple lines separated by newline characters
("\n"), or it may be a cellstr array with one element for each
line.  The optional @var{title} (character string) can be used to
decorate the dialog caption.

The string @var{default} identifies the default button,
which is activated by pressing the @key{ENTER} key.
It must match one of the strings given in @var{btn1}, @var{btn2}, or
@var{btn3}.

If only @var{msg} and @var{title} are specified, three buttons with
the default captions @qcode{"Yes"}, @qcode{"No"}, and @qcode{"Cancel"} are
used.

If only two button captions, @var{btn1} and @var{btn2}, are specified
the dialog will have only these two buttons.

@seealso{@ref{XREFerrordlg,,errordlg}, @ref{XREFhelpdlg,,helpdlg}, @ref{XREFinputdlg,,inputdlg}, @ref{XREFlistdlg,,listdlg}, @ref{XREFwarndlg,,warndlg}}
@end deftypefn


@cindex dialog, displaying a warning dialog
@c warndlg scripts/gui/warndlg.m
@anchor{XREFwarndlg}
@deftypefn  {Function File} {@var{h} =} warndlg (@var{msg})
@deftypefnx {Function File} {@var{h} =} warndlg (@var{msg}, @var{title})
Display @var{msg} using a warning dialog box.

The message may have multiple lines separated by newline characters
("\n"), or it may be a cellstr array with one element for each
line.  The optional input @var{title} (character string) can be used to
set the dialog caption.  The default title is @qcode{"Warning Dialog"}.

@seealso{@ref{XREFhelpdlg,,helpdlg}, @ref{XREFinputdlg,,inputdlg}, @ref{XREFlistdlg,,listdlg}, @ref{XREFquestdlg,,questdlg}}
@end deftypefn


@c ------------------------------------------------------------------------
@node FAQ - Frequently asked Questions
@section FAQ - Frequently asked Questions

@menu
* How to distinguish between Octave and Matlab?::
* How to make Java classes available?::
* How to create an instance of a Java class?::
* How can I handle memory limitations?::
* Which @TeX{} symbols are implemented in dialog functions?::
@end menu

@c ------------------------------------------------------------------------
@node How to distinguish between Octave and Matlab?
@subsection How to distinguish between Octave and Matlab?
@anchor{XREFFAQ}
@c - index -
@cindex Octave and @sc{matlab}, how to distinguish between
@c - index -

Octave and @sc{matlab} are very similar, but handle Java slightly different.
Therefore it may be necessary to detect the environment and use the appropriate
functions.  The following function can be used to detect the environment.  Due
to the persistent variable it can be called repeatedly without a heavy
performance hit.

Example:

@example
@group
%%
%% Return: true if the environment is Octave.
%%
function retval = isOctave
  persistent cacheval;  % speeds up repeated calls

  if isempty (cacheval)
    cacheval = (exist ("OCTAVE_VERSION", "builtin") > 0);
  end

  retval = cacheval;
end
@end group
@end example

@c ------------------------------------------------------------------------
@node How to make Java classes available?
@subsection How to make Java classes available to Octave?
@c - index -
@cindex classpath, setting
@cindex classpath, difference between static and dynamic
@cindex static classpath
@cindex dynamic classpath
@cindex @file{javaclasspath.txt}
@cindex @file{classpath.txt}
@cindex classes, making available to Octave
@c - index -

Java finds classes by searching a @var{classpath}.  This is a list of Java
archive files and/or directories containing class files.  In Octave
the @var{classpath} is composed of two parts:

@itemize
@item the @var{static classpath} is initialized once at startup of the JVM, and

@item the @var{dynamic classpath} which can be modified at runtime.
@end itemize

Octave searches the @var{static classpath} first, then the @var{dynamic
classpath}.  Classes appearing in the @var{static} as well as in the
@var{dynamic classpath} will therefore be found in the @var{static classpath}
and loaded from this location.  Classes which will be used frequently or must
be available to all users should be added to the @var{static classpath}.  The
@var{static classpath} is populated once from the contents of a plain text file
named @file{javaclasspath.txt} (or @file{classpath.txt} historically) when the
Java Virtual Machine starts.  This file contains one line for each individual
classpath to be added to the @var{static classpath}.  These lines can identify
single class files, directories containing class files, or Java archives with
complete class file hierarchies.  Comment lines starting with a @samp{#} or a
@samp{%} character are ignored.

The search rules for the file @file{javaclasspath.txt}
(or @file{classpath.txt}) are:

@itemize
@item First, Octave tries to locate it in the current directory (where Octave
was started from).  If such a file is found, it is read and defines the initial
@var{static classpath}.  Thus, it is possible to define a static classpath on a
'per Octave invocation' basis.

@item Next, Octave searches in the user's home directory.  If a file
@file{javaclasspath.txt} exists here, its contents are appended to the static
classpath (if any).  Thus, it is possible to build an initial static classpath
on a 'per user' basis.

@item Finally, Octave looks for a next occurrence of file
@file{javaclasspath.txt} in the m-files directory where Octave Java functions
live.  This is where @file{javaclasspath.m} resides, usually something like
@file{@w{@env{OCTAVE_HOME}}/share/octave/@w{@env{OCTAVE_VERSION}}/m/java/}.  You can
find this directory by executing the command

@example
which javaclasspath
@end example

If this file exists here, its contents are also appended to the static
classpath.  Note that the archives and class directories defined in this last
step will affect all users.
@end itemize

Classes which are used only by a specific script should be placed in the
@var{dynamic classpath}.  This portion of the classpath can be modified at
runtime using the @code{javaaddpath} and @code{javarmpath} functions.

Example:

@example
octave> base_path = "C:/Octave/java_files";

octave> % add two JARchives to the dynamic classpath
octave> javaaddpath ([base_path, "/someclasses.jar"]);
octave> javaaddpath ([base_path, "/moreclasses.jar"]);

octave> % check the dynamic classpath
octave> p = javaclasspath;
octave> disp (p@{1@});
C:/Octave/java_files/someclasses.jar
octave> disp (p@{2@});
C:/Octave/java_files/moreclasses.jar

octave> % remove the first element from the classpath
octave> javarmpath ([base_path, "/someclasses.jar"]);
octave> p = javaclasspath;
octave> disp (p@{1@});
C:/Octave/java_files/moreclasses.jar

octave> % provoke an error
octave> disp (p@{2@});
error: A(I): Index exceeds matrix dimension.
@end example

Another way to add files to the @var{dynamic classpath} exclusively for your
user account is to use the file @file{.octaverc} which is stored in your home
directory.  All Octave commands in this file are executed each time you start a
new instance of Octave.  The following example adds the directory @file{octave}
to Octave's search path and the archive @file{myclasses.jar} in this directory
to the Java search path.

@example
@group
% contents of .octaverc:
addpath ("~/octave");
javaaddpath ("~/octave/myclasses.jar");
@end group
@end example

@c ------------------------------------------------------------------------
@node How to create an instance of a Java class?
@subsection How to create an instance of a Java class?
@c - index -
@cindex object, how to create
@cindex instance, how to create
@c - index -

The function @code{javaObject} can be used to create Java objects..

Example:

@example
Passenger = javaObject ("package.FirstClass", row, seat);
@end example

@c ------------------------------------------------------------------------
@node How can I handle memory limitations?
@subsection How can I handle memory limitations?
@cindex memory, limitations

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 (@pxref{XREFjavamem,,javamem}).  The memory pool is shared by all
Java objects running in the JVM@.  This strict memory limit is intended mainly
to avoid that runaway applications inside web browsers or in enterprise servers
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
@file{java.opts}.  This is a text file where you can enter lines containing
@option{-X} and @option{-D} options handed to the JVM during initialization.

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

@example
which javaclasspath
@end example

The @option{-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 @file{java.opts} file:

@example
-Xmx256m
@end example

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 @file{java.opts} file starts the JVM with 64
Megabytes of initial memory:

@example
-Xms64m
@end example

For more details on the available @option{-X} options of your Java Virtual
Machine issue the command @samp{java -X} at the operating system command prompt
and consult the Java documentation.

The @option{-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 @code{getProperty()} methods of the @code{java.lang.System} class.
The following example line defines the property @var{MyProperty} and assigns it
the string @code{12.34}.

@example
-DMyProperty=12.34
@end example

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

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

@seealso{javamem}

@c ------------------------------------------------------------------------
@node Which @TeX{} symbols are implemented in dialog functions?
@subsection Which @TeX{} symbols are implemented in dialog functions?
@c - index -
@cindex symbols, translation table
@cindex @TeX{} symbols, translation table
@cindex translation table for @TeX{} symbols
@c - index -

The dialog functions contain a translation table for @TeX{} like symbol codes.
Thus messages and labels can be tailored to show some common mathematical
symbols or Greek characters.  No further @TeX{} formatting codes are supported.
 The characters are translated to their Unicode equivalent.  However, not all
characters may be displayable on your system.  This depends on the font used by
the Java system on your computer.

Each @TeX{} symbol code must be terminated by a space character to make it
distinguishable from the surrounding text.  Therefore the string @samp{\alpha
=12.0} will produce the desired result, whereas @samp{\alpha=12.0} would
produce the literal text @var{'\alpha=12.0'}.

@seealso{errordlg, helpdlg, inputdlg, listdlg, msgbox, questdlg, warndlg}

@need 5000
@c ---------------------------------
@ifhtml
@float Table
The table below shows each @TeX{} character code and the corresponding Unicode
character:
@multitable @columnfractions 0.18 0.1 0.05 0.18 0.1 0.05 0.18 0.1
@item \alpha
@tab 'α'
@tab
@tab \beta
@tab 'β'
@tab
@tab \gamma
@tab 'γ'
@c ----------
@item \delta
@tab 'δ'
@tab
@tab \epsilon
@tab 'ε'
@tab
@tab \zeta
@tab 'ζ'
@c ----------
@item \eta
@tab 'η'
@tab
@tab \theta
@tab 'θ'
@tab
@tab \vartheta
@tab 'ϑ'
@c ----------
@item \iota
@tab 'ι'
@tab
@tab \kappa
@tab 'κ'
@tab
@tab \lambda
@tab 'λ'
@c ----------
@item \mu
@tab 'μ'
@tab
@tab \nu
@tab 'ν'
@tab
@tab \xi
@tab 'ξ'
@c ----------
@item \pi
@tab 'π'
@tab
@tab \rho
@tab 'ρ'
@tab
@tab \sigma
@tab 'σ'
@c ----------
@item \varsigma
@tab 'ς'
@tab
@tab \tau
@tab 'τ'
@tab
@tab \phi
@tab 'φ'
@c ----------
@item \chi
@tab 'χ'
@tab
@tab \psi
@tab 'ψ'
@tab
@tab \omega
@tab 'ω'
@c ----------
@item \upsilon
@tab 'υ'
@tab
@tab \Gamma
@tab 'Γ'
@tab
@tab \Delta
@tab 'Δ'
@c ----------
@item \Theta
@tab 'Θ'
@tab
@tab \Lambda
@tab 'Λ'
@tab
@tab \Pi
@tab 'Π'
@c ----------
@item \Xi
@tab 'Ξ'
@tab
@tab \Sigma
@tab 'Σ'
@tab
@tab \Upsilon
@tab 'Υ'
@c ----------
@item \Phi
@tab 'Φ'
@tab
@tab \Psi
@tab 'Ψ'
@tab
@tab \Omega
@tab 'Ω'
@c ----------
@item \Im
@tab 'ℑ'
@tab
@tab \Re
@tab 'ℜ'
@tab
@tab \leq
@tab '≤'
@c ----------
@item \geq
@tab '≥'
@tab
@tab \neq
@tab '≠'
@tab
@tab \pm
@tab '±'
@c ----------
@item \infty
@tab '∞'
@tab
@tab \partial
@tab '∂'
@tab
@tab \approx
@tab '≈'
@c ----------
@item \circ
@tab '∘'
@tab
@tab \bullet
@tab '•'
@tab
@tab \times
@tab '×'
@c ----------
@item \sim
@tab '~'
@tab
@tab \nabla
@tab '∇'
@tab
@tab \ldots
@tab '…'
@c ----------
@item \exists
@tab '∃'
@tab
@tab \neg
@tab '¬'
@tab
@tab \aleph
@tab 'ℵ'
@c ----------
@item \forall
@tab '∀'
@tab
@tab \cong
@tab '≅'
@tab
@tab \wp
@tab '℘'
@c ----------
@item \propto
@tab '∝'
@tab
@tab \otimes
@tab '⊗'
@tab
@tab \oplus
@tab '⊕'
@c ----------
@item \oslash
@tab '⊘'
@tab
@tab \cap
@tab '∩'
@tab
@tab \cup
@tab '∪'
@c ----------
@item \ni
@tab '∋'
@tab
@tab \in
@tab '∈'
@tab
@tab \div
@tab '÷'
@c ----------
@item \equiv
@tab '≡'
@tab
@tab \int
@tab '∫'
@tab
@tab \perp
@tab '⊥'
@c ----------
@item \wedge
@tab '∧'
@tab
@tab \vee
@tab '∨'
@tab
@tab \supseteq
@tab '⊇'
@c ----------
@item \supset
@tab '⊃'
@tab
@tab \subseteq
@tab '⊆'
@tab
@tab \subset
@tab '⊂'
@c ----------
@item \clubsuit
@tab '♣'
@tab
@tab \spadesuit
@tab '♠'
@tab
@tab \heartsuit
@tab '♥'
@c ----------
@item \diamondsuit
@tab '♦'
@tab
@tab \copyright
@tab '©'
@tab
@tab \leftarrow
@tab '←'
@c ----------
@item \uparrow
@tab '↑'
@tab
@tab \rightarrow
@tab '→'
@tab
@tab \downarrow
@tab '↓'
@c ----------
@item \leftrightarrow
@tab '↔'
@tab
@tab \updownarrow
@tab '↕'
@tab
@c ----------
@end multitable
@caption{@TeX{} character codes and the resulting symbols.}
@end float
@end ifhtml
@c ---------------------------------
@iftex
@float Table
The table below shows each @TeX{} character code and the corresponding Unicode
character:
@multitable @columnfractions 0.18 0.1 0.05 0.18 0.1 0.05 0.18 0.1
@headitem @TeX{} code
@tab Symbol
@tab
@tab @TeX{} code
@tab Symbol
@tab
@tab @TeX{} code
@tab Symbol
@c ----------
@item \alpha
@tab '@math{\alpha}'
@tab
@tab \beta
@tab '@math{\beta}'
@tab
@tab \gamma
@tab '@math{\gamma}'
@c ----------
@item \delta
@tab '@math{\delta}'
@tab
@tab \epsilon
@tab '@math{\epsilon}'
@tab
@tab \zeta
@tab '@math{\zeta}'
@c ----------
@item \eta
@tab '@math{\eta}'
@tab
@tab \theta
@tab '@math{\theta}'
@tab
@tab \vartheta
@tab '@math{\vartheta}'
@c ----------
@item \iota
@tab '@math{\iota}'
@tab
@tab \kappa
@tab '@math{\kappa}'
@tab
@tab \lambda
@tab '@math{\lambda}'
@c ----------
@item \mu
@tab '@math{\mu}'
@tab
@tab \nu
@tab '@math{\nu}'
@tab
@tab \xi
@tab '@math{\xi}'
@c ----------
@item \pi
@tab '@math{\pi}'
@tab
@tab \rho
@tab '@math{\rho}'
@tab
@tab \sigma
@tab '@math{\sigma}'
@c ----------
@item \varsigma
@tab '@math{\varsigma}'
@tab
@tab \tau
@tab '@math{\tau}'
@tab
@tab \phi
@tab '@math{\phi}'
@c ----------
@item \chi
@tab '@math{\chi}'
@tab
@tab \psi
@tab '@math{\psi}'
@tab
@tab \omega
@tab '@math{\omega}'
@c ----------
@item \upsilon
@tab '@math{\upsilon}'
@tab
@tab \Gamma
@tab '@math{\Gamma}'
@tab
@tab \Delta
@tab '@math{\Delta}'
@c ----------
@item \Theta
@tab '@math{\Theta}'
@tab
@tab \Lambda
@tab '@math{\Lambda}'
@tab
@tab \Pi
@tab '@math{\Pi}'
@c ----------
@item \Xi
@tab '@math{\Xi}'
@tab
@tab \Sigma
@tab '@math{\Sigma}'
@tab
@tab \Upsilon
@tab '@math{\Upsilon}'
@c ----------
@item \Phi
@tab '@math{\Phi}'
@tab
@tab \Psi
@tab '@math{\Psi}'
@tab
@tab \Omega
@tab '@math{\Omega}'
@c ----------
@item \Im
@tab '@math{\Im}'
@tab
@tab \Re
@tab '@math{\Re}'
@tab
@tab \leq
@tab '@math{\leq}'
@c ----------
@item \geq
@tab '@math{\geq}'
@tab
@tab \neq
@tab '@math{\neq}'
@tab
@tab \pm
@tab '@math{\pm}'
@c ----------
@item \infty
@tab '@math{\infty}'
@tab
@tab \partial
@tab '@math{\partial}'
@tab
@tab \approx
@tab '@math{\approx}'
@c ----------
@item \circ
@tab '@math{\circ}'
@tab
@tab \bullet
@tab '@math{\bullet}'
@tab
@tab \times
@tab '@math{\times}'
@c ----------
@item \sim
@tab '@math{\sim}'
@tab
@tab \nabla
@tab '@math{\nabla}'
@tab
@tab \ldots
@tab '@math{\ldots}'
@c ----------
@item \exists
@tab '@math{\exists}'
@tab
@tab \neg
@tab '@math{\neg}'
@tab
@tab \aleph
@tab '@math{\aleph}'
@c ----------
@item \forall
@tab '@math{\forall}'
@tab
@tab \cong
@tab '@math{\cong}'
@tab
@tab \wp
@tab '@math{\wp}'
@c ----------
@item \propto
@tab '@math{\propto}'
@tab
@tab \otimes
@tab '@math{\otimes}'
@tab
@tab \oplus
@tab '@math{\oplus}'
@c ----------
@item \oslash
@tab '@math{\oslash}'
@tab
@tab \cap
@tab '@math{\cap}'
@tab
@tab \cup
@tab '@math{\cup}'
@c ----------
@item \ni
@tab '@math{\ni}'
@tab
@tab \in
@tab '@math{\in}'
@tab
@tab \div
@tab '@math{\div}'
@c ----------
@item \equiv
@tab '@math{\equiv}'
@tab
@tab \int
@tab '@math{\int}'
@tab
@tab \perp
@tab '@math{\perp}'
@c ----------
@item \wedge
@tab '@math{\wedge}'
@tab
@tab \vee
@tab '@math{\vee}'
@tab
@tab \supseteq
@tab '@math{\supseteq}'
@c ----------
@item \supset
@tab '@math{\supset}'
@tab
@tab \subseteq
@tab '@math{\subseteq}'
@tab
@tab \subset
@tab '@math{\subset}'
@c ----------
@item \clubsuit
@tab '@math{\clubsuit}'
@tab
@tab \spadesuit
@tab '@math{\spadesuit}'
@tab
@tab \heartsuit
@tab '@math{\heartsuit}'
@c ----------
@item \diamondsuit
@tab '@math{\diamondsuit}'
@tab
@tab \copyright
@tab '@math{\copyright}'
@tab
@tab \leftarrow
@tab '@math{\leftarrow}'
@c ----------
@item \uparrow
@tab '@math{\uparrow}'
@tab
@tab \rightarrow
@tab '@math{\rightarrow}'
@tab
@tab \downarrow
@tab '@math{\downarrow}'
@c ----------
@item \leftrightarrow
@tab '@math{\leftrightarrow}'
@tab
@tab \updownarrow
@tab '@math{\updownarrow}'
@tab
@c ----------
@end multitable
@caption{@TeX{} character codes and the resulting symbols.}
@end float
@end iftex
@c ---------------------------------
