What I wanted to do
As part of a larger project, I needed a simple text editor with line numbers. The editor should also be able to highlight the current line (line number in bold) and define the tab size.
The result looks like this:
My solution
After searching the internet for a while, I found out about the possibility of using a DocumentListener and adding a sepearate text-component with the line-numbers as RowHeader:
I also found this complete solution, but nevertheless implemented the class it on my own - for learning purposes.
My implementation of it looks like this:
import java.awt.Color;
import java.awt.Font;
import java.awt.Dimension;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.DocumentFilter;
import javax.swing.text.SimpleAttributeSet;
import javax.swing.text.StyleConstants;
/**
*
* @author Philipp Wilhelm
* Provides a JScrollPane with line-numbers
*/
public class EditorScrollPane extends JScrollPane {
private static final long serialVersionUID = 1L;
private JTextPane inputArea;
private String indentation = " ";
private JTextPane lineNumbers;
/*
* Here the constructor creates a TextPane as an editor-field and another TextPane for the
* line-numbers.
*/
public EditorScrollPane(int width, int height) {
// Editor-field
inputArea = new JTextPane();
inputArea.setPreferredSize(new Dimension(width, height));
Document doc = inputArea.getDocument();
// Replacing tabs with two spaces
((AbstractDocument) doc).setDocumentFilter(new DocumentFilter() {
public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs)
throws BadLocationException {
super.insertString(fb, offset, text.replace("\t", indentation), attrs);
}
});
// Line-numbers
lineNumbers = new JTextPane();
lineNumbers.setBackground(Color.GRAY);
lineNumbers.setEditable(false);
// Line-numbers should be right-aligned
SimpleAttributeSet rightAlign = new SimpleAttributeSet();
StyleConstants.setAlignment(rightAlign, StyleConstants.ALIGN_RIGHT);
lineNumbers.setParagraphAttributes(rightAlign, true);
doc.addDocumentListener(new DocumentListener() {
@Override
public void changedUpdate(DocumentEvent e) {
lineNumbers();
}
@Override
public void insertUpdate(DocumentEvent e) {
lineNumbers();
}
@Override
public void removeUpdate(DocumentEvent e) {
lineNumbers();
}
});
// Setting font
this.setFont(new Font("Monospaced", 12, Font.PLAIN));
// Sets the main-component in the JScrollPane. this.add(inputArea) wasn't
// enough in this case
this.getViewport().add(inputArea);
// Adds lineNumbers as row header on the left side of the main JTextPane
this.setRowHeaderView(lineNumbers);
}
private void lineNumbers() {
try {
String str = inputArea.getText();
// Plain Style
SimpleAttributeSet plain = new SimpleAttributeSet();
StyleConstants.setFontFamily(plain, "Monospaced");
StyleConstants.setFontSize(plain, 12);
// Bold style
SimpleAttributeSet bold = new SimpleAttributeSet();
StyleConstants.setBold(bold, true);
// Remove all from document
Document doc = lineNumbers.getDocument();
doc.remove(0, doc.getLength());
// Calculating the number of lines
int length = str.length() - str.replaceAll("\n", "").length() + 1;
// Adding line-numbers
for (int i = 1; i <= length; i++) {
// Non-bold line-numbers
if (i < length) {
doc.insertString(doc.getLength(), i + "\n", plain);
// Last line-number bold
} else {
doc.insertString(doc.getLength(), i + "\n", bold);
}
}
} catch (BadLocationException e) {
e.printStackTrace();
}
}
/*
* Setting indentation size in editor-field
*/
public void setIndentationSize(int size) {
String cache = indentation;
indentation = "";
for (int i = 0; i < size; i++) {
indentation += " ";
}
// Replace all previous indentations (at beginning of lines)
inputArea.setText(inputArea.getText().replaceAll(cache, indentation));
}
/*
* Overrides the method getText().
*/
public String getText() {
return inputArea.getText();
}
/*
* Overrides the method setText().
*/
public void setText(String str) {
inputArea.setText(str);
}
}
Minimal working example
If you want to test the class, you can use the following class to run the code:
// Just for testing purposes
import javax.swing.*;
public class Test {
public static void main(String[] args) {
// Frame
JFrame frame = new JFrame("Editor-Field");
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Panel
JPanel panel = new JPanel();
EditorScrollPane editor = new EditorScrollPane(400,400);
panel.add(editor);
frame.add(panel);
frame.pack();
frame.setVisible(true);
}
}
Questions
- How can this code be improved in general?
- Can the line-numbering be done in a more efficient way?
- Does this class miss anything important that you would expect from such a class?
