Tab char measuring in paragraph with right or center alignment.

The class below illustrates the problem

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 
import javax.swing.JButton;
import javax.swing.JFrame;

import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.text.BadLocationException;
import javax.swing.text.DefaultStyledDocument;
import javax.swing.text.Element;

import javax.swing.text.Style;
import javax.swing.text.StyleConstants;
import javax.swing.text.StyleContext;
 
public class RTFAlignmentStyle extends JFrame
{
	private static String message = ""; 
	private JButton center = null;
	private JButton left = null;
	private JButton right = null;
	JPanel jp = null;
	StyleContext context = null;
	DefaultStyledDocument document = null;
	Style style = null;
	JTextPane textPane = null;
	JScrollPane scrollPane = null;

 
	RTFAlignmentStyle()
	{
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
		context = new StyleContext();
		document = new DefaultStyledDocument(context);
 

		style = context.getStyle(StyleContext.DEFAULT_STYLE);
		StyleConstants.setAlignment(style, StyleConstants.ALIGN_LEFT); // decomment for left alignmnent
		StyleConstants.setFontSize(style, 24);
		StyleConstants.setSpaceAbove(style, 4);
		StyleConstants.setSpaceBelow(style, 4);
 
		try {
			document.insertString(document.getLength(), message, style);
		} catch (BadLocationException badLocationException) {

			badLocationException.printStackTrace();
		}
		textPane = new JTextPane(document);
		scrollPane = new JScrollPane(textPane);
		center = new JButton("Center");
		left = new JButton("Left");
		right = new JButton("Right");

 
		jp = new JPanel();
		jp.add(left);
		jp.add(center);
		jp.add(right);
 
		add(scrollPane, BorderLayout.CENTER);
		add(jp, BorderLayout.SOUTH );
 
		setSize(500, 150);
		setVisible(true);
 
		ActionListener al = new ActionListener()
		{

			Element el = null;
			public void actionPerformed(ActionEvent ae)
			{
				Style sty = null;
				if(ae.getActionCommand().equalsIgnoreCase("Center"))
				{

					StyleConstants.setAlignment(style,StyleConstants.ALIGN_CENTER);
					el = document.getParagraphElement(textPane.getCaretPosition());
					document.setParagraphAttributes(el.getStartOffset(),el.getEndOffset()-el.getStartOffset(),style,false);
				}else if(ae.getActionCommand().equalsIgnoreCase("Right"))
				{
					StyleConstants.setAlignment(style,StyleConstants.ALIGN_RIGHT);
					el = document.getParagraphElement(textPane.getCaretPosition());
					document.setParagraphAttributes(el.getStartOffset(),el.getEndOffset()-el.getStartOffset(),style,false);
				}else if(ae.getActionCommand().equalsIgnoreCase("Left"))
				{

					StyleConstants.setAlignment(style,StyleConstants.ALIGN_LEFT);
					el = document.getParagraphElement(textPane.getCaretPosition());
					document.setParagraphAttributes(el.getStartOffset(),el.getEndOffset()-el.getStartOffset(),style,true);
				}
				textPane.grabFocus();
			}
		};
 
		center.addActionListener(al);
		right.addActionListener(al);
		left.addActionListener(al);
	}

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

}

The problem is the 2 lines in ParagraphView
if(justification != StyleConstants.ALIGN_LEFT)
return x + 10.0f

and one more class with fixed behavior

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.text.*;

 
public class RTFAlignmentStyle extends JFrame
{
    private static String message = "";
    private JButton center = null;
    private JButton left = null;
    private JButton right = null;
    JPanel jp = null;
    StyleContext context = null;
    DefaultStyledDocument document = null;
    Style style = null;
    JTextPane textPane = null;
    JScrollPane scrollPane = null;

 
    RTFAlignmentStyle()
    {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        context = new StyleContext();
        document = new DefaultStyledDocument(context);
 

        style = context.getStyle(StyleContext.DEFAULT_STYLE);
        StyleConstants.setAlignment(style, StyleConstants.ALIGN_LEFT); // decomment for left alignmnent
        StyleConstants.setFontSize(style, 24);
        StyleConstants.setSpaceAbove(style, 4);
        StyleConstants.setSpaceBelow(style, 4);
 
        try {
            document.insertString(document.getLength(), message, style);
        } catch (BadLocationException badLocationException) {

            badLocationException.printStackTrace();
        }
        textPane = new JTextPane();
        textPane.setEditorKit( new MyEditorKit());
        textPane.setDocument(document);
        scrollPane = new JScrollPane(textPane);
        center = new JButton("Center");
        left = new JButton("Left");
        right = new JButton("Right");

 
        jp = new JPanel();
        jp.add(left);
        jp.add(center);
        jp.add(right);
 
        add(scrollPane, BorderLayout.CENTER);
        add(jp, BorderLayout.SOUTH );
 
        setSize(500, 150);
        setVisible(true);
 
        ActionListener al = new ActionListener()
        {

            Element el = null;
            public void actionPerformed(ActionEvent ae)
            {
                Style sty = null;
                if(ae.getActionCommand().equalsIgnoreCase("Center"))
                {

                    StyleConstants.setAlignment(style,StyleConstants.ALIGN_CENTER);
                    el = document.getParagraphElement(textPane.getCaretPosition());
                    document.setParagraphAttributes(el.getStartOffset(),el.getEndOffset()-el.getStartOffset(),style,false);
                }else if(ae.getActionCommand().equalsIgnoreCase("Right"))
                {
                    StyleConstants.setAlignment(style,StyleConstants.ALIGN_RIGHT);
                    el = document.getParagraphElement(textPane.getCaretPosition());
                    document.setParagraphAttributes(el.getStartOffset(),el.getEndOffset()-el.getStartOffset(),style,false);
                }else if(ae.getActionCommand().equalsIgnoreCase("Left"))
                {

                    StyleConstants.setAlignment(style,StyleConstants.ALIGN_LEFT);
                    el = document.getParagraphElement(textPane.getCaretPosition());
                    document.setParagraphAttributes(el.getStartOffset(),el.getEndOffset()-el.getStartOffset(),style,true);
                }
                textPane.grabFocus();
            }
        };
 
        center.addActionListener(al);
        right.addActionListener(al);
        left.addActionListener(al);
    }

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

 
}
class MyEditorKit extends StyledEditorKit {
    static char[] tabChars;
    /** Used for searching for a tab or decimal character. */

    static char[] tabDecimalChars;
 
    static {
        tabChars = new char[1];
        tabChars[0] = '\t';
        tabDecimalChars = new char[2];
        tabDecimalChars[0] = '\t';
        tabDecimalChars[1] = '.';
    }

 
    
    public ViewFactory getViewFactory() {
        return new StyledViewFactory();
    }
 
    class StyledViewFactory implements ViewFactory {

 
        public View create(Element elem) {
            String kind = elem.getName();
            if (kind != null) {
                if (kind.equals(AbstractDocument.ContentElementName)) {

                    return new LabelView(elem);
                }
                else if (kind.equals(AbstractDocument.ParagraphElementName)) {
                    return new MyParagraphView(elem);
                }

                else if (kind.equals(AbstractDocument.SectionElementName)) {
                    return new BoxView(elem, View.Y_AXIS);
                }
                else if (kind.equals(StyleConstants.ComponentElementName)) {

                    return new ComponentView(elem);
                }
                else if (kind.equals(StyleConstants.IconElementName)) {
                    return new IconView(elem);
                }

            }
 
            // default to text display
            return new LabelView(elem);
        }
 
    }

    class MyParagraphView extends ParagraphView {
 
        public MyParagraphView(Element elem) {
            super(elem);
        }

        public float nextTabStop(float x, int tabOffset) {
            float tabBase=getTabBase();
        // If the text isn't left justified, offset by 10 pixels!

//        if(justification != StyleConstants.ALIGN_LEFT)
//                return x + 10.0f;
            x -= tabBase;
            TabSet tabs = getTabSet();
            if(tabs == null) {
                // a tab every 72 pixels.
                return (float)(tabBase + (((int)x / 72 + 1) * 72));
            }

            return super.nextTabStop(x, tabOffset);
        }
    }
}