Alignment of text in JTextArea and JtextPane

Question

I have a following piece of code which uses JTextArea to display some text,

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
import javax.swing.text.DefaultCaret;

public class TextPane extends JFrame{
    public static TextPane instance;
    //private static JTextPane pane = new JTextPane(); //Uncomment to see alignment issue
    private static JTextArea pane = new JTextArea(); // alignment works fine
    private static JScrollPane scroll = new JScrollPane();
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                TextPane.getInstance().init();
            }
        });
    }
    private static TextPane getInstance() {
        if(null == instance){
            instance =  new TextPane();
        }
        return instance;
    }    
    private void init() {
        pane.setFont(new Font("Courier new", Font.PLAIN, 12)); 
        pane.setLayout(new BorderLayout());
        pane.setFocusCycleRoot(true);
        pane.setFocusTraversalKeysEnabled(false);
        pane.setBackground(Color.black);
        pane.setForeground(Color.white);
        pane.setCaretColor(Color.green);
        pane.setDragEnabled(false);
        pane.setText("IOC_CONFUG_MMM.lag    hkess.lag\t\t     papdifs.lag\r\nMemSys.lag.txt\t      eol.lag1\t\t     papdifs.lag2\r\nopp.lag\t\t      eol.lag2\t\t     papm_by.lag1\r\n");
        DefaultCaret caret = (DefaultCaret) pane.getCaret();
        caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
        scroll.setViewportView(pane);
        add(scroll);     
        setTitle("Test");
        setSize(800 , 800);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setResizable(true);
        setVisible(true);
    }
}

There was an issue in alignment of the setText string initially however after i add font as Courier New i got it resolved(if i remove setFont alignment will not work.)

recently due to some requirements i changed from JtextArea to JTextPane , now with same piece of code the text doesn't align properly in JTextPane but if i change it to JTextArea alignment works fine.

I couldn't understand this behaviour. How can i achieve the alignment in JTextPane. please help.

Answer 1

The JTextPane (or the editor kit you are using implicitly) has a different default behavior regarding tab placement which stems from the fact that it is intended to contain far more complex content than a JTextArea. You can create your desired simple fixed-width font tab placement manually and set it explicitly. Just insert the following lines right before invoking setText(…); on your pane:

int w=pane.getFontMetrics(pane.getFont()).charWidth(' ');
TabStop[] stops={ new TabStop(0), new TabStop(w*8), new TabStop(w*16),
  new TabStop(w*24), new TabStop(w*32), new TabStop(w*40), new TabStop(w*48),
  new TabStop(w*56), new TabStop(w*64), new TabStop(w*72), new TabStop(w*80) };
MutableAttributeSet attrs=new SimpleAttributeSet();
StyleConstants.setTabSet(attrs, new TabSet(stops) );
pane.setParagraphAttributes(attrs, false);