Package com.wolfram.jlink

Interface KernelLink

  • All Superinterfaces:
    MathLink
    public interface KernelLink
extends MathLink
    KernelLink is the main link interface that J/Link programmers will use. The MathLink interface contains the low-level methods for reading and writing data. KernelLink extends the MathLink interface, adding some higher-level methods that are appropriate only if the program on the other side of the link is a Mathematica kernel. An example is the discardAnswer() method, which reads and discards the sequence of packets the kernel will send in the course of a single evaluation.

    Objects of type KernelLink are created by the createKernelLink() method in the MathLinkFactory class.

    See Also:
    MathLink, MathLinkFactory

    • Field Detail

      • VERSION

        static final java.lang.String VERSION
        The version string identifying this release.
        See Also:
        Constant Field Values

      • VERSION_NUMBER

        static final double VERSION_NUMBER
        The major version number identifying this release.
        See Also:
        Constant Field Values

      • PACKAGE_CONTEXT

        static final java.lang.String PACKAGE_CONTEXT
        The Mathematica package context for the J/Link support functions. Using this is preferable to hard-coding "JLink`" in your code if you need to explicitly load the J/Link package file. 
             BAD:  ml.evaluate("Needs[\"JLink`\"]");
     GOOD: ml.evaluate("Needs[\" + KernelLink.PACKAGE_CONTEXT + \"]");
        See Also:
        Constant Field Values

      • MLTKOBJECT

        static final int MLTKOBJECT
        Returned by the KernelLink methods getNext() and getType() to represent that a Java object is waiting to be read from the link. This is an extension to the MLTKxxx constants in the MathLink interface.
        See Also:
        Constant Field Values

      • TYPE_OBJECT

        static final int TYPE_OBJECT
        This is an extension to the TYPE_xxx constants in the MathLink interface used in getArray().
        See Also:
        Constant Field Values

      • MLE_BAD_OBJECT

        static final int MLE_BAD_OBJECT
        Error code in a MathLinkException when getObject() was called and a valid Java object was not on the link.
        See Also:
        Constant Field Values

    • Method Detail

      • evaluate

        void evaluate​(java.lang.String s)
       throws MathLinkException
        Sends a string for evaluation.

        This method only sends the computation--it does not read any resulting packets off the link. You would typically follow a call to evaluate() with either waitForAnswer() or discardAnswer(), which read data from the link.

        Parameters:
        s - the string of Mathematica code
        Throws:
        MathLinkException
        See Also:
        waitForAnswer(), discardAnswer()

      • evaluate

        void evaluate​(Expr e)
       throws MathLinkException
        Sends an Expr for evaluation.

        This method only sends the computation--it does not read any resulting packets off the link. You would typically follow a call to evaluate() with either waitForAnswer() or discardAnswer(), which read data from the link.

        Parameters:
        e - the Expr to evaluate
        Throws:
        MathLinkException

      • evaluateToInputForm

        java.lang.String evaluateToInputForm​(java.lang.String s,
                                     int pageWidth)
        Sends a string to evaluate, then reads and discards all output except for the result, which is returned. The result comes back in Mathematica InputForm, formatted to the specified page width.
        Parameters:
        s - the string to evaluate
        pageWidth - the page width, in characters, to format the output
        Returns:
        the answer in InputForm, or null if a MathLinkException occurred

      • evaluateToInputForm

        java.lang.String evaluateToInputForm​(Expr e,
                                     int pageWidth)
        Sends an Expr to evaluate, then reads and discards all output except for the result, which is returned. The result comes back in Mathematica InputForm, formatted to the specified page width.
        Parameters:
        e - the Expr to evaluate
        pageWidth - the page width, in characters, to format the output. Pass 0 for Infinity
        Returns:
        the answer in InputForm, or null if a MathLinkException occurred
        See Also:
        getLastError()

      • evaluateToOutputForm

        java.lang.String evaluateToOutputForm​(java.lang.String s,
                                      int pageWidth)
        Sends a string to evaluate, then reads and discards all output except for the result, which is returned. The result comes back in Mathematica OutputForm, formatted to the specified page width.
        Parameters:
        s - the string to evaluate
        pageWidth - the page width, in characters, to format the output. Pass 0 for Infinity
        Returns:
        the answer in InputForm, or null if a MathLinkException occurred
        See Also:
        getLastError()

      • evaluateToOutputForm

        java.lang.String evaluateToOutputForm​(Expr e,
                                      int pageWidth)
        Sends an Expr to evaluate, then reads and discards all output except for the result, which is returned. The result comes back in Mathematica OutputForm, formatted to the specified page width.
        Parameters:
        e - the Expr to evaluate
        pageWidth - the page width, in characters, to format the output. Pass 0 for Infinity
        Returns:
        the answer in InputForm, or null if a MathLinkException occurred
        See Also:
        getLastError()

      • evaluateToImage

        byte[] evaluateToImage​(java.lang.String s,
                       int width,
                       int height)
        Sends graphics or plotting code to evaluate, then reads and discards all output except for the image data, which is returned as a byte array of GIF data. The image will be sized to just fit within a box of width X height, without changing its aspect ratio. In other words, the image might not have exactly these dimensions, but it will never be larger.

        To get image data returned in JPEG format instead of GIF, set the Mathematica symbol JLink`$DefaultImageFormat = "JPEG".

        If s does not evaluate to a graphics expression, then null is returned. It is not enough that the computation causes a plot to be generated--the return value of the computation must be a Mathematica Graphics (or Graphics3D, SurfaceGraphics, etc.) expression. For example: 

             BAD:  ml.evaluateToImage("Plot[x,{x,0,1}]; 42");
     GOOD: ml.evaluateToImage("Plot[x,{x,0,1}]");
        To create an Image from the data, you can do the following: 
             byte[] gifData = ml.evaluateToImage(someInput, 0, 0);
     java.awt.Image im = java.awt.Toolkit.getDefaultToolkit().createImage(gifData);
        Parameters:
        s - the string to evaluate
        width - the image width, in pixels. Pass 0 for Automatic, or if the expression itself specifies the width
        height - the image height, in pixels. Pass 0 for Automatic, or if the expression itself specifies the height
        Returns:
        the GIF data, or null if s does not evaluate to a graphics expression or if a MathLinkException occurred
        See Also:
        getLastError()

      • evaluateToImage

        byte[] evaluateToImage​(Expr e,
                       int width,
                       int height)
        Sends graphics or plotting code to evaluate, then reads and discards all output except for the image data, which is returned as a byte array of GIF data. The image will be sized to just fit within a box of width X height, without changing its aspect ratio. In other words, the image might not have exactly these dimensions, but it will never be larger.

        To get image data returned in JPEG format instead of GIF, set the Mathematica symbol JLink`$DefaultImageFormat = "JPEG".

        If e does not evaluate to a graphics expression, then null is returned. It is not enough that the computation causes a plot to be generated--the return value of the computation must be a Mathematica Graphics (or Graphics3D, SurfaceGraphics, etc.) expression.

        To create an Image from the data, you can do the following: 

             byte[] gifData = ml.evaluateToImage(someInput, 0, 0);
     java.awt.Image im = java.awt.Toolkit.getDefaultToolkit().createImage(gifData);
        Parameters:
        e - the Expr to evaluate
        width - the image width, in pixels. Pass 0 for Automatic, or if the expression itself specifies the width
        height - the image height, in pixels. Pass 0 for Automatic, or if the expression itself specifies the height
        Returns:
        the GIF data, or null if e does not evaluate to a graphics expression or if a MathLinkException occurred
        See Also:
        getLastError()

      • evaluateToImage

        byte[] evaluateToImage​(java.lang.String s,
                       int width,
                       int height,
                       int dpi,
                       boolean useFE)
        Sends graphics or plotting code to evaluate, then reads and discards all output except for the image data, which is returned as a byte array of GIF data. The image will be sized to just fit within a box of width X height, without changing its aspect ratio. In other words, the image might not have exactly these dimensions, but it will never be larger. The image resolution, in dots per inch, is specified by dpi. The useFE parameter controls whether the notebook front end will be used for rendering services. If it is used, the front end will be run on the same machine as the kernel.

        To get image data returned in JPEG format instead of GIF, set the Mathematica symbol JLink`$DefaultImageFormat = "JPEG".

        If s does not evaluate to a graphics expression, then null is returned. It is not enough that the computation causes a plot to be generated--the return value of the computation must be a Mathematica Graphics (or Graphics3D, SurfaceGraphics, etc.) expression. For example: 

             BAD:  ml.evaluateToImage("Plot[x,{x,0,1}]; 42");
     GOOD: ml.evaluateToImage("Plot[x,{x,0,1}]");
        To create an Image from the data, you can do the following: 
             byte[] gifData = ml.evaluateToImage(someInput, 0, 0, 0, false);
     java.awt.Image im = java.awt.Toolkit.getDefaultToolkit().createImage(gifData);
        Parameters:
        s - the string to evaluate
        width - the image width, in pixels. Pass 0 for Automatic, or if the expression itself specifies the width
        height - the image height, in pixels. Pass 0 for Automatic, or if the expression itself specifies the height
        dpi - the resolution, in dots (pixels) per inch. Pass 0 for Automatic, or if the expression itself specifies the resolution
        useFE - whether to use the notebook front end for rendering services
        Returns:
        the GIF data, or null if s does not evaluate to a graphics expression or if a MathLinkException occurred
        See Also:
        getLastError()

      • evaluateToImage

        byte[] evaluateToImage​(Expr e,
                       int width,
                       int height,
                       int dpi,
                       boolean useFE)
        Sends graphics or plotting code to evaluate, then reads and discards all output except for the image data, which is returned as a byte array of GIF data. The image will be sized to just fit within a box of width X height, without changing its aspect ratio. In other words, the image might not have exactly these dimensions, but it will never be larger. The image resolution, in dots per inch, is specified by dpi. The useFE parameter controls whether the notebook front end will be used for rendering services. If it is used, the front end will be run on the same machine as the kernel.

        To get image data returned in JPEG format instead of GIF, set the Mathematica symbol JLink`$DefaultImageFormat = "JPEG".

        If s does not evaluate to a graphics expression, then null is returned. It is not enough that the computation causes a plot to be generated--the return value of the computation must be a Mathematica Graphics (or Graphics3D, SurfaceGraphics, etc.) expression.

        To create an Image from the data, you can do the following: 

             byte[] gifData = ml.evaluateToImage(someInput, 0, 0, 0, false);
     java.awt.Image im = java.awt.Toolkit.getDefaultToolkit().createImage(gifData);
        Parameters:
        e - the Expr to evaluate
        width - the image width, in pixels. Pass 0 for Automatic, or if the expression itself specifies the width
        height - the image height, in pixels. Pass 0 for Automatic, or if the expression itself specifies the height
        dpi - the resolution, in dots (pixels) per inch. Pass 0 for Automatic, or if the expression itself specifies the resolution
        useFE - whether to use the notebook front end for rendering services
        Returns:
        the GIF data, or null if s does not evaluate to a graphics expression or if a MathLinkException occurred
        See Also:
        getLastError()

      • evaluateToTypeset

        byte[] evaluateToTypeset​(java.lang.String s,
                         int width,
                         boolean useStdForm)
        Sends a string to evaluate, the result of which will be typeset, converted to a GIF, and the resulting data returned. The result is typeset in StandardForm if useStdForm is true, and TraditionalForm otherwise. The result will be wrapped to width pixels during typesetting. The notebook front end will be used for rendering services; it will be run on the same machine as the kernel.

        To create an Image from the data, you can do the following: 

             byte[] gifData = ml.evaluateToTypeset(someInput, 0, true);
     java.awt.Image im = java.awt.Toolkit.getDefaultToolkit().createImage(gifData);
        Parameters:
        s - the string to evaluate
        width - the width to wrap the output to during typesetting, in pixels (a rough measure). Pass 0 for Infinity
        useStdForm - true for StandardForm, false for TraditionalForm
        Returns:
        the GIF data, or null if a MathLinkException occurred
        See Also:
        getLastError()

      • evaluateToTypeset

        byte[] evaluateToTypeset​(Expr e,
                         int width,
                         boolean useStdForm)
        Sends an Expr to evaluate, the result of which will be typeset, converted to a GIF, and the resulting data returned. The result is typeset in StandardForm if useStdForm is true, and TraditionalForm otherwise. The result will be wrapped to width pixels during typesetting. The notebook front end will be used for rendering services; it will be run on the same machine as the kernel.

        To create an Image from the data, you can do the following: 

             byte[] gifData = ml.evaluateToTypeset(someInput, 0, true);
     java.awt.Image im = java.awt.Toolkit.getDefaultToolkit().createImage(gifData);
        Parameters:
        e - the Expr to evaluate
        width - the width to wrap the output to during typesetting, in pixels (a rough measure). Pass 0 for Infinity
        useStdForm - true for StandardForm, false for TraditionalForm
        Returns:
        the GIF data, or null if a MathLinkException occurred
        See Also:
        getLastError()

      • getLastError

        java.lang.Throwable getLastError()
        Returns the Throwable object that represents any exception detected during the last call of one of the "evaluateTo" methods (evaluateToInputForm(), evaluateToOutputForm(), evaluateToImage(), evaluateToTypeset()). For convenience, those methods don't throw MathLinkException. Instead, they catch any such exceptions and simply return null if one occurred. Sometimes you want to see what the exact exception was when you get back a null result. The getLastError() method shows you that exception. Typically, it will be a MathLinkException, but there are some other rare cases (like an OutOfMemoryError if an image was returned that would have been too big to handle).
        Returns:
        the exception, or null if no exception occurred

      • waitForAnswer

        int waitForAnswer()
           throws MathLinkException
        Reads and discards all packets that arrive up until the packet that contains the result of the computation. It is then your responsibility to read the contents of the packet that holds the result.

        Use this after sending an expression to evaluate with evaluate() or a manual sequence of put methods. 

             ml.evaluate("2+2");
     ml.waitForAnwser();
     int result = ml.getInteger();
     // It is not strictly necessary to call newPacket, since we have read the entire
     // packet contents, but it is good style.
     ml.newPacket();
        If you are not interested in examining the result of the evaluation, use discardAnswer() instead.

        Examples of packets that arrive before the result and are discarded are TEXTPKT, MESSAGEPKT, DISPLAYPKT, etc. If you want to examine or operate on the incoming packets that are discarded by this method, use the PacketListener interface.

        It returns the packet type that held the result of the computation. Typically, this will be RETURNPKT. However, if you are manually sending evaluations inside an EnterTextPacket or EnterExpressionPacket, there are some further issues that you need to understand; consult the J/Link User Guide for details.

        Returns:
        the packet type that held the result, typically RETURNPKT
        Throws:
        MathLinkException
        See Also:
        discardAnswer(), evaluate(String), evaluate(Expr)

      • discardAnswer

        void discardAnswer()
            throws MathLinkException
        Reads and discards all packets generated during a computation.

        Use this after sending an expression to evaluate with evaluate() or a manual sequence of put methods.

        If you are interested in examining the result of the evaluation, use waitForAnswer() instead.

        If you want to examine or operate on the incoming packets that are discarded by this method, use the PacketListener interface.

        Throws:
        MathLinkException
        See Also:
        waitForAnswer(), evaluate(String), evaluate(Expr)

      • handlePacket

        void handlePacket​(int pkt)
           throws MathLinkException
        Call this to invoke J/Link's internal handling of special packet types.

        If you absolutely must write your own packet loop instead of using the PacketListener interface (this is strongly discouraged), you should call this method if a call to nextPacket() returns a packet type that you are not handling entirely with your own code. In fact, you can call handlePacket() for every packet you read with nextPacket(). For example, here is a basic packet loop: 

             boolean done = false;
     while (!done) {
          int pkt = ml.nextPacket();
          if (ml.notifyPacketListeners(pkt))
              ml.handlePacket(pkt);
          switch (pkt) {
              case MathLink.RETURNPKT:
                  // read and handle contents of ReturnPacket ...
                  done = true;
                  break;
              case MathLink.TEXTPKT:
                  // read and handle contents of TextPacket ...
                  break;
              .. etc for other packet types
          }
          ml.newPacket();
     }
        To remind again, writing your own packet loop like this is strongly discouraged. Use waitForAnswer(), discardAnswer(), or one of the "evaluateTo" methods instead. These methods hide the packet loop within them. If you want more information about what packet types arrive and their contents, simply use the PacketListener interface.

        An example of the special type of packets that your packet loop might encounter is CALLPKT. Encountering a CALLPKT means that Mathematica code is trying to call into Java using the mechanism described in Part 1 of the J/Link User Guide. Only the internals of J/Link know how to manage these callbacks, so the handlePacket() method provides a means to invoke this handling for you.

        If you are using waitForAnswer(), discardAnswer(), or any of the "evaluateTo" methods, and therefore not writing your own packet loop, you do not need to be concerned with handlePacket().

        After handlePacket() returns you should call newPacket().

        Throws:
        MathLinkException
        See Also:
        waitForAnswer()

      • put

        void put​(java.lang.Object obj)
  throws MathLinkException
        Sends an object.

        Behaves like the put(Object) method in the MathLink interface for objects that have a meaningful "value" representation in Mathematica. This set is: 

         null: sent as the symbol Null.
 strings: sent as Mathematica strings
 arrays: sent as lists of the appropriate dimensions
 Expr: sent as expressions
 Wrapper classes (e.g., Boolean, Integer, Float, etc.): sent as their values
 BigDecimal and BigInteger: sent as their values
 complex numbers: sent as Complex
        For other objects, behaves like putReference(). In other words, the KernelLink interface changes the semantics of put(Object) compared to the MathLink interface by adding the ability to send object references to Mathematica for objects whose values are not meaningful. You must call enableObjectReferences() before calling put(Object) on an object that will be sent by reference. See notes for putReference().
        Specified by:
        put in interface MathLink
        Parameters:
        obj - the object to send
        Throws:
        MathLinkException
        See Also:
        putReference(Object), enableObjectReferences()

      • putReference

        void putReference​(java.lang.Object obj)
           throws MathLinkException
        Sends an object to Mathematica "by reference". You must call enableObjectReferences() before calling putReference().

        Use this method to pass Java objects to Mathematica so that methods can be invoked directly from Mathematica code as described in Part 1 of the J/Link User Guide.

        The put() method will also put some objects by reference, but there are two reasons to call putReference() instead: 

         (1) You want to force an object that would normally be sent by value
 (for example, a string) to be sent by reference.
 (2) You know that the object is a type that put() will send by
 reference. By calling putReference() directly, you can save the
 effort put() would expend figuring this out.
        Parameters:
        obj - the object to send
        Throws:
        MathLinkException
        See Also:
        put(Object), enableObjectReferences(), getObject()

      • getNext

        int getNext()
     throws MathLinkException
        Extends the MathLink method of the same name by allowing the extra return type MLTKOBJECT. This type is returned whenever a JavaObject expression is waiting on the link. Note that the symbol Null, although it is a valid Java object reference, will cause getNext() to return MLTKSYM, not MLTKOBJECT.
        Specified by:
        getNext in interface MathLink
        Returns:
        one of MLTKINT, MLTKREAL, MLTKSTR, MLTKSYM, MLTKFUNC
        Throws:
        MathLinkException
        See Also:
        MathLink.getNext(), enableObjectReferences()

      • getType

        int getType()
     throws MathLinkException
        Extends the MathLink method of the same name by allowing the extra return type MLTKOBJECT. This type is returned whenever a JavaObject expression is waiting on the link. Note that the symbol Null, although it is a valid Java object reference, will cause getType() to return MLTKSYM, not MLTKOBJECT.
        Specified by:
        getType in interface MathLink
        Returns:
        one of MLTKINT, MLTKREAL, MLTKSTR, MLTKSYM, MLTKFUNC
        Throws:
        MathLinkException
        See Also:
        MathLink.getType(), enableObjectReferences()

      • getArray

        java.lang.Object getArray​(int type,
                          int depth)
                   throws MathLinkException
        Extends the MathLink method of the same signature by allowing the extra type specification TYPE_OBJECT. This method allows you to read arrays of object references (i.e, arrays of JavaObject expressions).
        Specified by:
        getArray in interface MathLink
        Parameters:
        type - The desired type for the returned array. Must be one of TYPE_BOOLEAN, TYPE_BYTE, TYPE_CHAR, TYPE_SHORT, TYPE_INT, TYPE_LONG, TYPE_FLOAT, TYPE_DOUBLE, TYPE_STRING, TYPE_BIGINTEGER, TYPE_BIGDECIMAL, TYPE_EXPR, or TYPE_COMPLEX.
        depth - the depth of the returned array
        Returns:
        the array read, or null if type is TYPE_COMPLEX and no Java class has been declared for complex numbers via setComplexClass()
        Throws:
        MathLinkException - if the incoming expression is not an array of the requested type or is not as deep as requested
        See Also:
        MathLink.getArray(int, int), enableObjectReferences()

      • getArray

        java.lang.Object getArray​(int type,
                          int depth,
                          java.lang.String[] heads)
                   throws MathLinkException
        Extends the MathLink method of the same signature by allowing the extra type specification TYPE_OBJECT. This method allows you to read arrays of object references (i.e, arrays of JavaObject expressions).
        Specified by:
        getArray in interface MathLink
        Parameters:
        type - The desired type for the returned array. Must be one of TYPE_BOOLEAN, TYPE_BYTE, TYPE_CHAR, TYPE_SHORT, TYPE_INT, TYPE_LONG, TYPE_FLOAT, TYPE_DOUBLE, TYPE_STRING, TYPE_BIGINTEGER, TYPE_BIGDECIMAL, TYPE_EXPR, or TYPE_COMPLEX.
        depth - the depth of the returned array
        heads - an array of length 'depth' that will be filled with the heads at each level
        Returns:
        the array read, or null if type is TYPE_COMPLEX and no Java class has been declared for complex numbers via setComplexClass()
        Throws:
        MathLinkException - if the incoming expression is not an array of the requested type, or is not as deep as requested
        See Also:
        MathLink.getArray(int, int, String[]), enableObjectReferences()

      • getArray

        java.lang.Object getArray​(java.lang.Class elementType,
                          int depth)
                   throws MathLinkException
        An improvement on the KernelLink.getArray(int type, int depth) signature that allows you to specify the type of array to create when reading arrays of Java objects. The old getArray(int type, int depth) method only allowed you to specify TYPE_OBJECT as the type, and this would result in the creation of an array of objects with an element type determined by the first object in the incoming array. This causes problems for arrays of objects of mixed types. For example, if you were reading a list of two objects from Mathematica where the first element of the list was a Frame object and the second was an Exception object, then calling getArray(KernelLink.TYPE_OBJECT, 1) would cause J/Link to examine the first element (a Frame) and then create a Frame[] to hold all the elements. The next object read is not a Frame, however, and this causes an error. This version of the getArray() method allows you to specify that the created array should be typed only as Object[], which allows both the Frame and the Exception to be stored in the same array: 
              Object[] a = (Object[]) ml.getArray(Object.class, 1);
        Throws:
        MathLinkException
        Since:
        4.2
        See Also:
        MathLink.getArray(int, int), getArray(Class, int, String[]), enableObjectReferences()

      • getArray

        java.lang.Object getArray​(java.lang.Class elementType,
                          int depth,
                          java.lang.String[] heads)
                   throws MathLinkException
        An improvement on the KernelLink.getArray(int type, int depth, String[] heads) signature that allows you to specify the type of array to create when reading arrays of Java objects. See the documentation for the KernelLink.getArray(Class, int) method for more information. This signature fills a String array with the heads of the expression found at each level.
        Throws:
        MathLinkException
        Since:
        4.2
        See Also:
        MathLink.getArray(int, int, String[]), getArray(Class, int), enableObjectReferences()

      • enableObjectReferences

        void enableObjectReferences()
                     throws MathLinkException
        Call this method to enable the ability to pass Java objects "by reference" to Mathematica. You must call this before attempting to call putReference(), or put() on an object that will be put by reference.

        This method requires that the JLink.m file be present in the JLink directory (its default location if J/Link is properly installed).

        Throws:
        MathLinkException
        See Also:
        enableObjectReferences(boolean), putReference(Object)

      • enableObjectReferences

        Expr enableObjectReferences​(boolean becomeDefaultJVM)
                     throws MathLinkException
        Call this method to enable the ability to pass Java objects "by reference" to Mathematica. This version of the method supplants the earlier no-argument version by allowing you to specify a boolean argument that controls whether you want the calling Java runtime to become the default target for J/Link calls from Mathematica into Java. The typical choice for this argument is true, and this is the behavior you get if you call enableObjectReferences() with no arguments. Advanced programmers might want to attach a Java runtime to Mathematica and enable J/Link callbacks into the runtime without it becoming the default target. This is done by calling enableObjectReferences(false). Note that the calling JVM will still become the default target even if false is passed in the case where no other Java runtime is currently attached to Mathematica.

        The method returns the JVM expression that you can use in UseJVM or other constructs to identify this Java runtime as the target for calls from Java into Mathematica.

        You must call this before attempting to call putReference(), or put() on an object that will be put by reference.

        This method requires that the JLink.m file be present in the JLink directory (its default location if J/Link is properly installed).

        Returns:
        the JVM expression you can use to identify the current runtime in Mathematica code
        Throws:
        MathLinkException
        Since:
        4.0
        See Also:
        enableObjectReferences(), putReference(Object)

      • addPacketListener

        void addPacketListener​(PacketListener listener)
        Adds the specified PacketListener to receive PacketArrivedEvents.

        Use this method to register a PacketListener object to receive notifications when packets are read by any of the KernelLink methods that run internal packet loops. These methods are: waitForAnswer(), discardAnswer(), evaluateToInputForm(), evaluateToOutputForm(), evaluateToImage(), and evaluateToTypeset().

        J/Link programmers are discouraged from writing their own packet loops (i.e., repeatedly calling nextPacket() and newPacket() until a desired packet arrives). Instead, they should create a class that implements PacketListener, register an object of this class using addPacketListener(), and then use the KernelLink methods that manage the packet loop for you.

        Parameters:
        listener - the PacketListener to register
        See Also:
        removePacketListener(PacketListener), PacketArrivedEvent, PacketPrinter

      • notifyPacketListeners

        boolean notifyPacketListeners​(int pkt)
        Call this method to invoke the normal notification of registered PacketListeners if you are manually reading packets with nextPacket().

        The KernelLink methods that run internal packet loops (waitForAnswer(), discardAnswer(), evaluateToInputForm(), evaluateToOutputForm(), evaluateToImage(), and evaluateToTypeset()) call this method for each packet to trigger the notification of registered PacketListeners. If you are reading packets yourself by calling nextPacket() (this is discouraged), you can call notifyPacketListeners() to cause PacketListeners to be notified for these packets as well. Call it right after nextPacket(), passing it the packet type as returned by nextPacket(). The state of the link (the current position in the incoming data stream) will be unaffected by the call.

        Parameters:
        pkt - the packet type (as returned by nextPacket())
        Returns:
        true, if one of the listeners wanted to suppress default packet handling; you will probably ignore this
        See Also:
        removePacketListener(PacketListener), addPacketListener(PacketListener)

      • getClassLoader

        JLinkClassLoader getClassLoader()
        Gets the JLinkClassLoader that is used by this link to load classes via the LoadJavaClass[] Mathematica function.

        In rare cases programmers might need to obtain the class loader that J/Link uses to load classes from Mathematica. One reason for this is if you want to load a class in Java code that is found in the special set of extra locations that J/Link's class loader knows about (such as Java subdirectories of Mathematica application directories; see the J/Link User Guide for more information on how J/Link finds classes). Another reason is if want to obtain a class object from a class name and the class has already been loaded from a special location by J/Link's class loader. Class cls = Class.forName("Some.class.that.only.JLink.can.find", ml.getClassLoader()); If you are calling this method from a standalone Java program you should first call enableObjectReferences() to initialize the class loader with the special Mathematica-specific locations for Java classes.

        See Also:
        setClassLoader(JLinkClassLoader), enableObjectReferences(), JLinkClassLoader

      • setClassLoader

        void setClassLoader​(JLinkClassLoader loader)
        Sets the JLinkClassLoader that is used by this link to load classes via the LoadJavaClass[] Mathematica function.

        Advanced programmers might need to specify the class loader that J/Link will use to load classes from Mathematica. The only reason to do this is if you want the class loader to have a specific parent loader, because that parent loader has certain capabilities or can load classes from certain locations that J/Link would otherwise not know about. KernelLink ml = MathLinkFactory.createKernelLink(...); ml.discardAnswer(); ml.setClassLoader(new JLinkClassLoader(mySpecialParentClassLoader)); ml.enableObjectReferences(); This method can only be called in a standalone Java program (i.e., not in Java code called from Mathematica), and should be called before enableObjectReferences().

        See Also:
        getClassLoader(), enableObjectReferences(), JLinkClassLoader

      • abortEvaluation

        void abortEvaluation()
        Sends a request to the kernel to abort the current evaluation.

        This method is typically called from a different thread than the one that is performing the computation. That "computation" thread is typically blocking in waitForAnswer() or some other method that is waiting for the result to arrive from Mathematica. If you want to abort the computation so that the main thread does not have to continue waiting, you can call abortEvaluation() on some other thread (perhaps in response to some user action like clicking an "abort" button). The computation will terminate and return the symbol $Aborted. Be aware that Mathematica is not always in a state where it is receptive to abort requests. A quick return of $Aborted is not always guaranteed.

        What this method does is simply send an MLABORTMESSAGE to the kernel. It is provided for convenience to shield programmers from such low-level details.

        Since:
        2.0
        See Also:
        interruptEvaluation(), abandonEvaluation(), terminateKernel()

      • interruptEvaluation

        void interruptEvaluation()
        Sends a request to the kernel to interrupt the current evaluation. Interrupt requests should not be confused with abort requests. Interrupt requests generate a special MenuPacket from the kernel that needs a response. You must be prepared to handle this packet if you call interruptEvaluation(). You can use the com.wolfram.jlink.ui.InterruptDialog class for this if you choose.

        This method is typically called from a different thread than the one that is performing the computation. That "computation" thread is typically blocking in waitForAnswer() or some other method that is waiting for the result to arrive from Mathematica. If you want to interrupt the computation to provide your users with choices ("abort", "continue", "enter dialog", etc.), you can call interruptEvaluation() on some other thread (perhaps in response to the user clicking an "interrupt" button). Be aware that Mathematica is not always in a state where it is receptive to interrupt requests.

        What this method does is simply send an MLINTERRUPTMESSAGE to the kernel. It is provided for convenience to shield programmers from such low-level details.

        Since:
        2.0
        See Also:
        InterruptDialog, abortEvaluation(), abandonEvaluation(), terminateKernel()

      • abandonEvaluation

        void abandonEvaluation()
        Causes any method that is blocking waiting for output from the kernel to return immediately and throw a MathLinkException. This is a "last-ditch" method when you absolutely want to break out of any methods that are waiting for a result from the kernel. The link should always be closed after you call this.

        This method is typically called from a different thread than the one that is performing the computation. That "computation" thread is typically blocking in waitForAnswer() or some other method that is waiting for the result to arrive from Mathematica. If you want to force that method to return immediately (it will throw a MathLinkException), call abandonEvaluation(). The code in the catch handler for the MathLinkException will find that clearError() returns false, indicating that the link is irrecoverably damaged. You should then call terminateKernel() followed by close().

        Since:
        2.0
        See Also:
        abortEvaluation(), interruptEvaluation(), terminateKernel()

      • terminateKernel

        void terminateKernel()
        Sends a request to the kernel to shut down.

        Most of the time, when you call close() on a link, the kernel will quit. If the kernel is busy with a computation, however, it will not stop just because the link closes. Use terminateKernel() to force the kernel to quit even though it may be busy. This is not an operating system-level "kill" command, and it is not absolutely guaranteed that the kernel will die immediately.

        This method is safe to call from any thread. Any method that is blocking waiting for a result from Mathematica (such as waitForAnswer()) will return immediately and throw a MathLinkException. You will typically call close() immediately after terminateKernel(), as the link will die when the kernel quits.

        A typical usage scenario is as follows. You have a thread that is blocking in waitForAnswer() waiting for the result of some computation, and you decide that it must return right away and you are willing to sacrifice the kernel to guarantee this. You then call abandonEvaluation() on a separate thread. This causes waitForAnswer() to immediately throw a MathLinkException. You catch this exception, discover that clearError() returns false indicating that the link is hopeless, and then you call terminateKernel() followed by close(). The reason terminateKernel() is useful here is that because you called abandonEvaluation(), the kernel may still be computing and it may not die when you call close(). You call terminateKernel() to give it a little help.

        What this method does is simply send an MLTERMINATEMESSAGE to the kernel. It is provided for convenience to shield programmers from such low-level details.

        Since:
        2.0
        See Also:
        abortEvaluation(), interruptEvaluation(), abandonEvaluation()

      • print

        void print​(java.lang.String s)
        Prints the specified text in the user's Mathematica session.

        This method is usable only in Java code that is invoked in a call from Mathematica, as described in Part 1 of the J/Link User Guide. In other words, it is only used in code that is called from a Mathematica session via the "installable Java" mechanism. Programmers who are launching the kernel and controlling it from Java code will have no use for this method.

        The KernelLink object on which this method will be called will probably be obtained via StdLink.getLink().

        Parameters:
        s - the text to print
        See Also:
        message(String, String), message(String, String[])

      • message

        void message​(java.lang.String symtag,
             java.lang.String arg)
        Prints the specified message in the user's Mathematica session.

        Use this form for messages that take at most 1 argument to be spliced into their text.

        This method is usable only in Java code that is invoked in a call from Mathematica, as described in Part 1 of the J/Link User Guide. In other words, it is only used in code that is called from a Mathematica session via the "installable Java" mechanism. Programmers who are launching the kernel and controlling it from Java code will have no use for this method.

        The KernelLink object on which this method will be called will probably be obtained via StdLink.getLink().

        Parameters:
        symtag - the message designation, in the usual Symbol::tag style
        arg - a string to be spliced into the message text, in the same way it would be used by Mathematica's Message function. Pass null if no arguments are needed.
        See Also:
        message(String, String[]), print(String)

      • message

        void message​(java.lang.String symtag,
             java.lang.String[] args)
        Prints the specified message in the user's Mathematica session.

        Use this form for messages that take more than one argument to be spliced into their text.

        This method is usable only in Java code that is invoked in a call from Mathematica, as described in Part 1 of the J/Link User Guide. In other words, it is only used in code that is called from a Mathematica session via the "installable Java" mechanism. Programmers who are launching the kernel and controlling it from Java code will have no use for this method.

        The KernelLink object on which this method will be called will probably be obtained via StdLink.getLink().

        Parameters:
        symtag - the message designation, in the usual Symbol::tag style, like Mathematica's Message function
        args - an array of strings to be spliced into the message text, in the same way as they are used by Mathematica's Message function.
        See Also:
        message(String, String), print(String)

      • beginManual

        void beginManual()
        Informs J/Link that your code will be manually sending the result back to Mathematica. This circumvents the normal automatic return of whatever the method being called returns.

        This method is usable only in Java code that is invoked in a call from Mathematica, as described in Part 1 of the J/Link User Guide. In other words, it is only used in code that is called from a Mathematica session via the "installable Java" mechanism. Programmers who are launching the kernel and controlling it from Java code will have no use for this method.

        The KernelLink object on which this method will be called will probably be obtained via StdLink.getLink().

        The name "beginManual" was chosen instead of, say, "setManual" to emphasize that the link enters a special mode the moment this method is called. To allow the most graceful exception handling, you should delay calling beginManual() until right before you begin to write the result on the link.

      • wasInterrupted

        boolean wasInterrupted()
        Tells whether the user has attempted to abort the computation.

        This method is usable only in Java code that is invoked in a call from Mathematica, as described in Part 1 of the J/Link User Guide. In other words, it is only used in code that is called from a Mathematica session via the "installable Java" mechanism. Programmers who are launching the kernel and controlling it from Java code will have no use for this method.

        When the user tries to interrupt a Mathematica computation that is in the middle of a call into Java, the interrupt request is sent to Java. If a Java method makes no attempt to honor interrupt requests, then after the method call completes J/Link will execute the Mathematica function Abort[], causing the entire computation to end and return the result $Aborted. If you want to detect interrupts within a Java method, for example to break out of a long Java computation, call wasInterrupted() to determine if an interrupt request has been received. If it returns true, then you can simply return from your method, and J/Link will take care of calling Abort[] for you. If the method returns a value, the value will be ignored. For example, you could put code like the following into a time-intensive loop you were running: 

             KernelLink ml = StdLink.getLink();
     if (ml.wasInterrupted())
         return;
        If you want to do something other than call Abort[] in response to the interrupt you should call beginManual(), send back a result manually, and then call clearInterrupt(). The clearInterrupt() method tels J/Link that you have handled the interrupt manually and therefore J/Link should not try to send back Abort[]: 
             KernelLink ml = StdLink.getLink();
     if (ml.wasInterrupted()) {
         try {
             ml.beginManual();
             ml.put("Interrupted at iteration " + i);
             ml.clearInterrupt();
         } catch (MathLinkException e) {}
         return;
     }
        Returns:
        true, if the user tried to interrupt the execution from their Mathematica session; false otherwise
        See Also:
        clearInterrupt()

      • clearInterrupt

        void clearInterrupt()
        Call this method after you have handled an interrupt request manually. See the documentation for the wasInterrupted() method for more information.

        This method is usable only in Java code that is invoked in a call from Mathematica, as described in Part 1 of the J/Link User Guide. In other words, it is only used in code that is called from a Mathematica session via the "installable Java" mechanism. Programmers who are launching the kernel and controlling it from Java code will have no use for this method.

        See Also:
        wasInterrupted(), beginManual()