Modify multiple JTextFields with a DocumentListener

Question

This is my very first java swing application in school. We had to do a caesar coder.(http://en.wikipedia.org/wiki/Caesar_cipher)

It should know to crypt and decrypt and it should do it automaticly even if you don't press the button. (FocusListener)

It works like a dream, until I only have to do it with the "Code!" button. Then we had to add a DocumentListener, which I created, as shown below. It works if I use it only to crypt or only to decrypt. The problem occurs, when I add both JTextField to the same DocumentListener. I get an IllegalStateException with an "AWT-EventQueue-0" label. It calls the setText function two times, and the second one is fatal. I think it is because if I type a character to the first JTextField it is an insert, then when I set the content of the second JTextField with setText it is an insert too. Our prof said it can be fixed easily with a flag, but I'm failing. Can you help me please?

Application.java

    package javaswinglabor;

    public class Application {
        public static void main(String[] args) {
        CaesarFrame caesarFrame = new CaesarFrame();
        }
    }

CaesarProgram.java

package javaswinglabor;

public class CaesarProgram {

    /**
     * Caesar kodolo
     * @param input
     * @param offset
     * @return kod
     */
    static String caesarCoder(String input, char offset){
        input = input.toUpperCase();
        String kod="";
        for(int i=0; i < input.length(); i++){
        if(input.charAt(i) >= 'A' && input.charAt(i) <= 'Z' ) {
            kod += (char)(65 + ((input.charAt(i) - 'A' + offset - 'A')%26) );
        }
        }
        return kod;
    }

    /**
     * Caesar dekodolo
     * @param input
     * @param offset
     * @return kod
     */
    static String caesarDecoder(String input, char offset){
    input = input.toUpperCase();
    String kod="";
    for(int i=0; i < input.length(); i++){
        if(input.charAt(i) >= 'A' && input.charAt(i) <= 'Z' ) {
        kod += (char)(65 + (input.charAt(i) - offset + 26)%26 );
        }
    }
    return kod;
    }
}

CaesarFrame.java

 package javaswinglabor;

import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.HeadlessException;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

public class CaesarFrame extends JFrame{



    //TOP JPanel
    private JComboBox cb;
    private JTextField t1;
    private JButton b;

    //DOWN JPanel
    private JTextField t2;

    //encrypt/decrypt
    private boolean encrypt;



    public CaesarFrame() throws HeadlessException {
    super("SwingLab");
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    this.setSize(400, 110);
    this.setResizable(true);
    this.setLayout(new GridLayout(2, 3));

    JPanel pFelso = new JPanel(new FlowLayout(FlowLayout.LEFT));
    JPanel pAlso = new JPanel(new FlowLayout(FlowLayout.LEFT));
    this.add(pFelso);
    this.add(pAlso);

    //TOP Jpanel
    cb = new JComboBox(fillObject());
    t1 = new JTextField(20);
    b = new JButton("Code!");
    pFelso.add(cb);
    pFelso.add(t1);
    pFelso.add(b);

    //DOWN JPanel
    t2 = new JTextField(20);
    //t2.setEditable(false);
    pAlso.add(new JLabel("Output:"));
    pAlso.add(t2);

    //ButtonListener
    OkButtonActionListener obl = new OkButtonActionListener();
    b.addActionListener(obl);

    //DocumentListeners
    CoderDocumentFilter cdf = new CoderDocumentFilter();
    DecoderDocumentFilter ddf = new DecoderDocumentFilter();
    ((AbstractDocument)(t1.getDocument())).setDocumentFilter((cdf));
    ((AbstractDocument)(t2.getDocument())).setDocumentFilter((ddf));

    //InputFieldKeyListener ifkl = new InputFieldKeyListener();
    //t1.addKeyListener(ifkl);

    //SpecialDocumentListener t1_dl = new SpecialDocumentListener();
    //t1.getDocument().addDocumentListener(t1_dl);
    //t2.getDocument().addDocumentListener(t1_dl);

    //FocusListener
    JTextFieldFocusListener jtfl = new JTextFieldFocusListener();
    t1.addFocusListener(jtfl);
    t2.addFocusListener(jtfl);

    this.pack();
    this.setVisible(true);
    }



    private void Coder(){
    Character c = (Character)cb.getSelectedItem();
    t2.setText( CaesarProgram.caesarCoder(t1.getText(), c.charValue()) );
    }
    private void Decoder(){
    Character c = (Character)cb.getSelectedItem();
    t1.setText( CaesarProgram.caesarDecoder(t2.getText(), c.charValue()) );
    }



    private class CoderDocumentFilter extends DocumentFilter{
    @Override public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
        super.insertString(fb, offset, text.toUpperCase(), attr);
        if (encrypt) {Coder();}
    }
    @Override public void replace (DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attr) throws BadLocationException {
        super.replace(fb, offset, length, text.toUpperCase(), attr);
        if (encrypt) {Coder();}
    }
    @Override public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException{
        super.remove(fb, offset, length);
        if (encrypt) {Coder();}
    }
    }



    private class DecoderDocumentFilter extends DocumentFilter{
    @Override public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
        super.insertString(fb, offset, text.toUpperCase(), attr);
        if (!encrypt) {Decoder();}
    }
    @Override public void replace (DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attr) throws BadLocationException {
        super.replace(fb, offset, length, text.toUpperCase(), attr);
        if (!encrypt) {Decoder();}
    }
    @Override public void remove(DocumentFilter.FilterBypass fb, int offset, int length) throws BadLocationException{
        super.remove(fb, offset, length);
        if (!encrypt) {Decoder();}
    }
    }



    /**
     * Egy 26-elemu Object tombot tolt fel az angol ABC nagybetuivel.
     * @return object[]
     */
    private static Object[] fillObject() {
    Object[] object = new Object[26];
    for(int i=0; i < 26; i++){
        object[i] = (char)(i+65);
    }
    return object;
    }



    //Button listener
    private class OkButtonActionListener implements ActionListener{
    @Override
    public void actionPerformed(ActionEvent ae) {
        if(encrypt){Coder();}
        else{Decoder();}
    }
    }



    //FocusListener
    private class JTextFieldFocusListener implements FocusListener {

    @Override public void focusGained(FocusEvent fe) {
        if(t1.isFocusOwner()) {encrypt = true;}
        else if(t2.isFocusOwner()){encrypt = false;}
    }

    @Override public void focusLost(FocusEvent fe) {}
    }



    //Previous task
    /*
    private class InputFieldKeyListener extends KeyAdapter {
    @Override public void keyPressed(KeyEvent ke) {
        super.keyPressed(ke);
        Character c = (Character)cb.getSelectedItem();
        String s = String.valueOf(ke.getKeyChar());
        t2.setText(t2.getText() + CaesarProgram.caesarCoder(s, c.charValue()) );
    }
    }
    */
}

I solved the problem, thank you all, for your useful help. I'm sure it isn't the most elegant or the fastest solution, but it works finally. I would be glad, if somebody would like to make it more efficent or easier/cleaner.

Answer 1

From How to Write a Document Listener:

Document listeners should not modify the contents of the document; The change is already complete by the time the listener is notified of the change.

To fix this problem, use a DocumentFilter rather than a DocumentListener.

See this example Implementing a Document Filter

Answer 2

As has already being stated, you should be using a DocumentFilter instead of trying to modify the fields using a DocumentListener

The sample below demonstrates the basic idea. I had lots of fun getting your decode/encode methods to work, so I wrote my own ;)

Check out MDP's Weblog for some additional examples and Text Component Features for more information (there's a section on document filters)

public class TestCeaserCipher {

    public static final int OFFSET = 13;

    public static void main(String[] args) {
        new TestCeaserCipher();
    }

    public TestCeaserCipher() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new CeaserCiperPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    protected class CeaserCiperPane extends JPanel {

        private JTextField encode;
        private JTextField decode;

        public CeaserCiperPane() {
            encode = new JTextField(12);
            decode = new JTextField(12);

            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.fill = GridBagConstraints.HORIZONTAL;
            gbc.weightx = 1;
            add(encode, gbc);
            gbc.gridy++;
            add(decode, gbc);

            ((AbstractDocument) encode.getDocument()).setDocumentFilter(new EncodeFilter());
            ((AbstractDocument) decode.getDocument()).setDocumentFilter(new DecodeFilter());
        }
    }

    public class EncodeFilter extends DocumentFilter {
        @Override
        public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
            text = encode(text);
            super.replace(fb, offset, length, text, attrs);
        }

        @Override
        public void insertString(FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
            text = encode(text);
            super.insertString(fb, offset, text, attr);

        }
    }

    public class DecodeFilter extends DocumentFilter {
        @Override
        public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
            text = decode(text);
            super.replace(fb, offset, length, text, attrs);
        }

        @Override
        public void insertString(FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
            text = decode(text);
            super.insertString(fb, offset, text, attr);
        }
    }

    public static String encode(String text) {
        StringBuilder ciper = new StringBuilder(text.length());
        for (int index = 0; index < text.length(); index++) {
            ciper.append(TestCeaserCipher.encode(text.charAt(index), OFFSET));
        }

        return ciper.toString();
    }

    public static String decode(String text) {
        StringBuilder ciper = new StringBuilder(text.length());
        for (int index = 0; index < text.length(); index++) {
            ciper.append(TestCeaserCipher.decdoe(text.charAt(index), OFFSET));
        }

        return ciper.toString();
    }

    public static char encode(char input, int offset) {
        char encode = Character.toUpperCase(input);
        if (encode >= 'A' && encode <= 'Z') {

            int min = (int)'A';
            int max = (int)'Z';

            int value = (encode - offset);

            if (value < min) {
                value++;
                value = min - value;
                value = max - value;
            }

            encode = (char)value;

        }
        return encode;
    }

    public static char decdoe(char input, int offset) {
        char decode = Character.toUpperCase(input);
        if (decode >= 'A' && decode <= 'Z') {

            int min = (int)'A';
            int max = (int)'Z';

            int value = decode + offset;
            if (value > max) {
                value--;
                value = value - max;
                value = min + value;
            }

            decode = (char)value;

        }
        return decode;
    }

}