import javax.swing.*;
 
/**
 * Main frame for the program.
 * @author Bill
 *
 */
public class MainFrame extends JFrame {
    private static final long serialVersionUID = -7853618434340029314L;
    JTextPane editor = null;
    SyntaxDocument2 sd = null;
 
    /**
     * Make a main frame.
     */
    public MainFrame() {
        this.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        editor = new JTextPane();
        sd = new SyntaxDocument2( editor );
        this.setSize( 500, 500 );
        editor.setDocument( sd );
        this.add( editor );
        this.setVisible( true );
    }
 
    /**
     * entry point of the program
     * @param args command line arguments
     */
    public static void main(String[] args) {
        new MainFrame();
    }
}

/**
 * 
 */
import java.awt.Color;
 
import javax.swing.JTextPane;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DefaultStyledDocument;
import javax.swing.text.SimpleAttributeSet;
import javax.swing.text.StyleConstants;
 
 
/**
 * @author Bill
 *
 */
public class SyntaxDocument2 extends DefaultStyledDocument {
    private static final long serialVersionUID = 8802669064394912853L;
    SimpleAttributeSet norm = new SimpleAttributeSet();
    SimpleAttributeSet tag = new SimpleAttributeSet();
    SimpleAttributeSet string = new SimpleAttributeSet();
    private JTextPane jp = null; // A reference to a JTextPane
 
    /**
     * Sets some stuff up.
     */
    public SyntaxDocument2( JTextPane jp ) {
    	this.jp = jp;  // assigning the passed reference to the globally scoped one
        StyleConstants.setForeground( tag, Color.green );
        StyleConstants.setForeground( string, Color.red );
    }
    /**
     * @see javax.swing.text.AbstractDocument#insertString(int, java.lang.String, javax.swing.text.AttributeSet)
     */
    @Override
    public void insertString( int offs, String str, AttributeSet a )
            throws BadLocationException {
        super.insertString( offs, str, a );
 
        String str2 = super.getText( 0, super.getLength() );
 
 
        super.remove( 0, super.getLength() );
 
        int off = 0;
        char c;
        boolean inTag=false;
        boolean inString=false;
        for(int i = 0;i<str2.length();i++,off++) {
            c=str2.charAt( i );
 
            switch( c ) {
            case '<':
                inTag=true;
                super.insertString( off, ""+c, tag );
                break;
            case '>':
                inTag=false;
                super.insertString( off, ""+c, tag );
                break;
            case '"':
                if(inTag) {
                    inString=!inString;
                    super.insertString( off, ""+c, string );
                } else {
                    super.insertString( off, ""+c, norm );
                }
                break;
            default:
                if(inTag) {
                    if(inString) {
                        super.insertString( off, ""+c, string );
                    } else {
                        super.insertString( off, ""+c, tag );                        
                    }
                } else {
                    super.insertString( off, ""+c, norm );
                }
                break;
            }
        }
 
        /*
         * Assuming the '^' char is our cursor,
         * the desired result for input into the document
         * is as follows--
         * 
         * [H, i, , T, h,^ r, e]
         * [1, 2, 3, 4, 5, 6, 7]
         * 
         * after inserting e past h,
         * 
         * [H, i, , T, h, e,^ r, e]
         * [1, 2, 3, 4, 5, 6, 7, 8]
         * 
         * -- basically we want the cursor to act like a regular
         * cursor in a text document. That is, we want the cursor
         * to increment by one after we insert a character into the
         * document.
         * 
         * http://java.sun.com/javase/6/docs/api/javax/swing/text/Caret.html
         * Shows the Caret API used in the JTextPane. Although a JTextPane
         * will view/modify its Document, ultimately the interface needed to
         * operate on the JTextPane itself is its Caret.
         * 
         * I'm assuming that the JTextPane is listening for property and
         * key events, but I'm not entirely sure of the exact relationship
         * between the events occurring on the pane and the Caret's position.
         * 
         * This is an expirimental solution. There may be a way to send a
         * hint to the JTextPane (a flag, or maybe another command) such that
         * the Caret can be placed without requiring a reference to an existing
         * JTextPane. This method may not be incredibly practical, but it does
         * form a solution.
         */
 
        jp.getCaret().setDot(offs+1);
 
    }
}

        String str2 = super.getText( 0, super.getLength() );
 
        super.remove( 0, super.getLength() );

        String str2 = super.getText( 0, offs+str.length() );

        super.remove( 0, str2.length() );