2.10.3 A Sample Program that Displays Graphics and Typeset Results

Here is the code for a simple program that presents a window that displays Mathematica graphics and typeset output. It is an example of how to use the MathCanvas class. The code and compiled class files for this program are available in the JLink/Examples/Part2/GraphicsApp directory. Launch the program with the pathname to the kernel executable as an argument (note the use of the quote marks " and '):

(Windows)

java -classpath GraphicsApp.jar;..\..\..\JLink.jar GraphicsApp "c:\program files\wolfram research\mathematica\5.0\mathkernel"



(Unix)

java -classpath GraphicsApp.jar:../../../JLink.jar GraphicsApp 'math -mathlink'



(Mac OSX command line)

java -classpath GraphicsApp.jar:../../../JLink.jar GraphicsApp '"/Applications/Mathematica 5.0.app/Contents/MacOS/MathKernel" -mathlink'

Here is the code.

import com.wolfram.jlink.*;

import java.awt.*;

import java.awt.event.*;



public class GraphicsApp extends Frame {



    static GraphicsApp app;

    static KernelLink ml;

    

    MathCanvas mathCanvas;

    TextArea inputTextArea;

    Button evalButton;

    Checkbox useFEButton;

    Checkbox graphicsButton;

    Checkbox typesetButton;



    public static void main(String[] argv) {



        try {

            String[] mlArgs = {"-linkmode", "launch", "-linkname", argv[0]};

            ml = MathLinkFactory.createKernelLink(mlArgs);

            ml.discardAnswer();

        } catch (MathLinkException e) {

            System.out.println("An error occurred connecting to the kernel.");

            if (ml != null)

                ml.close();

            return;

        }

        app = new GraphicsApp();

    }



    public GraphicsApp() {

        

        setLayout(null);

        setTitle("Graphics App");

        mathCanvas = new MathCanvas(ml);

        add(mathCanvas);

        mathCanvas.setBackground(Color.white);

        inputTextArea = new TextArea("", 2, 40, TextArea.SCROLLBARS_VERTICAL_ONLY);

        add(inputTextArea);

        evalButton = new Button("Evaluate");

        add(evalButton);

        evalButton.addActionListener(new BnAdptr());

        useFEButton = new Checkbox("Use front end", false);

        CheckboxGroup cg = new CheckboxGroup();

        graphicsButton = new Checkbox("Show graphics output", true, cg);

        typesetButton = new Checkbox("Show typeset result", false, cg);

        add(useFEButton);

        add(graphicsButton);

        add(typesetButton);

        

        setSize(300, 400);

        setLocation(100,100);

        mathCanvas.setBounds(10, 25, 280, 240);

        inputTextArea.setBounds(10, 270, 210, 60);

        evalButton.setBounds(230, 290, 60, 30);

        graphicsButton.setBounds(20, 340, 160, 20);

        typesetButton.setBounds(20, 365, 160, 20);

        useFEButton.setBounds(180, 340, 100, 20);

        

        addWindowListener(new WnAdptr());

        setBackground(Color.lightGray);

        setResizable(false);

        

        // Although this code would automatically be called in

        // evaluateToImage or evaluateToTypeset, it can cause the

        // front end window to come in front of this Java window.

        // Thus, it is best to get it out of the way at the start

        // and call toFront to put this window back in front.

        // KernelLink.PACKAGE_CONTEXT is just "JLink`", but it is

        // preferable to use this symbolic constant instead of

        // hard-coding the package context.

        ml.evaluateToInputForm("Needs[\"" + KernelLink.PACKAGE_CONTEXT + "\"]", 0);

        ml.evaluateToInputForm("ConnectToFrontEnd[]", 0);

        

        setVisible(true);

        toFront();

    }





    class BnAdptr implements ActionListener {

        public void actionPerformed(ActionEvent e) {

            mathCanvas.setImageType(

                graphicsButton.getState() ? MathCanvas.GRAPHICS : MathCanvas.TYPESET);

            mathCanvas.setUsesFE(useFEButton.getState());

            mathCanvas.setMathCommand(inputTextArea.getText());

        }

    }

    

    class WnAdptr extends WindowAdapter {

        public void windowClosing(WindowEvent event) {

            if (ml != null) {

                // Because we used the front end, it is important

                // to call CloseFrontEnd[] before closing the link.

                // Counterintuitively, this is not because we want

                // to force the front end to quit, but because we

                // _don't_ want to do this if the user has begun

                // working in the front end session we started.

                // CloseFrontEnd knows how to politely disengage

                // from the front end if necessary. The need for

                // this will go away in future releases of

                // Mathematica.

                ml.evaluateToInputForm("CloseFrontEnd[]", 0);

                ml.close();

            }

            dispose();

            System.exit(0);

        }

    }

}