I'm using a JTextArea in a JFrame. I would like the tab key to insert four spaces instead of a tab.
The method setTabSize does not work, as it puts a tab ('\t') in the contents of the text area.
How can I have JTextArea insert four spaces instead of a tab whenever I press the tab key? That way the getText() method will return indentations of four spaces for every tab.
I would avoid using KeyListeners (as a general rule with JTextComponents) and even Key Bindings, since while Key Bindings would work for keyboard input, it wouldn't work for copy-and-paste.
In my mind, the best way is to use a DocumentFilter set on the JTextArea's Document (which is a PlainDocument, by the way). This way, even if you copy and paste text into the JTextAreas, one with tabs, then all the tabs will automatically be converted to 4 spaces on insertion.
For example:
import javax.swing.*;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;
import javax.swing.text.PlainDocument;
public class TestTextArea {
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> {
JTextArea textArea = new JTextArea(20, 50);
JScrollPane scrollPane = new JScrollPane(textArea);
int spaceCount = 4;
((PlainDocument) textArea.getDocument()).setDocumentFilter(new ChangeTabToSpacesFilter(spaceCount));
JFrame frame = new JFrame("GUI");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(scrollPane);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
});
}
private static class ChangeTabToSpacesFilter extends DocumentFilter {
private int spaceCount;
private String spaces = "";
public ChangeTabToSpacesFilter(int spaceCount) {
this.spaceCount = spaceCount;
for (int i = 0; i < spaceCount; i++) {
spaces += " ";
}
}
@Override
public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr)
throws BadLocationException {
string = string.replace("\t", spaces);
super.insertString(fb, offset, string, attr);
}
@Override
public void remove(FilterBypass fb, int offset, int length) throws BadLocationException {
super.remove(fb, offset, length);
}
@Override
public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs)
throws BadLocationException {
text = text.replace("\t", spaces);
super.replace(fb, offset, length, text, attrs);
}
}
}
So now, even if I copy and paste a document with tabs within it, into the JTextArea, all tabs will be automatically replaced with spaceCount spaces.
This is one of those “I wonder if…” moments.
Personally, I’d try a tackle the problem more directly, at the source. This means “trapping” the Tab event some how and “replacing” it’s functionality.
So, I started by modifying http://www.java2s.com/Tutorial/Java/0260__Swing-Event/ListingtheKeyBindingsinaComponent.htm, which could list the key bindings for component, for this, I found that the JTextArea was using insert-tab as the action map key.
I then created my own Action designed to insert spaces at the current caret position, for example…
public class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
// insert-tab
JTextArea ta = new JTextArea(10, 20);
add(new JScrollPane(ta));
ActionMap am = ta.getActionMap();
am.put("insert-tab", new SpacesTabAction());
}
public class SpacesTabAction extends AbstractAction {
@Override
public void actionPerformed(ActionEvent e) {
if (!(e.getSource() instanceof JTextArea)) {
return;
}
JTextArea textArea = (JTextArea) e.getSource();
int caretPosition = textArea.getCaretPosition();
Document document = textArea.getDocument();
try {
document.insertString(caretPosition, " ", null);
} catch (BadLocationException ex) {
ex.printStackTrace();
}
}
}
}
}
This will not cover pasting the text into the component, which would otherwise be covered by a DocumentFilter, but, I like to think about scenarios where a DocumentFilter might not be usable (such as having one already installed)
The method setTabSize does not work, as it puts a tab ('\t') in the contents of the text area.
Is this one of those “spaces vs tabs” flame wars :P
I did some fiddling and discovered that, most of the inconsistencies with setTabSize came about from not using a fixed width font, for example…
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
public class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
setLayout(new BorderLayout());
Font font = Font.decode("Courier New").deriveFont(12);
JTextArea ta = new JTextArea(10, 40);
ta.setFont(font);
ta.setText("---|----|----|----|----|----|----|----|\n\tHello");
ta.setTabSize(0);
add(new JScrollPane(ta));
DefaultComboBoxModel<Integer> model = new DefaultComboBoxModel<>(new Integer[] {0, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24});
JComboBox<Integer> tabSizes = new JComboBox<>(model);
add(tabSizes, BorderLayout.NORTH);
tabSizes.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
Integer tabSize = (Integer)tabSizes.getSelectedItem();
ta.setTabSize(tabSize);
}
});
}
}
}
When I set the font to “Courier New”, I was able to get a consistent indentation which was in align with the set tab size
The tab is four spaces. In this "111\t" string, the tab is expands to 1 space; "22\t" — to 2 spaces; "3\t" — to 3 spaces; finally, "\t" expands to four spaces.
Yes, isn't this the expected behaviour?!
JTextArea, tabSize of 4, mono spaced font
Sublime text editor, tabSize of 4, mono spaced font
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Font;
import java.util.StringJoiner;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
StringJoiner textJoiner = new StringJoiner("\n");
for (int row = 0; row < 10; row++) {
StringJoiner rowJoiner = new StringJoiner("\t");
for (int col = 0; col < 10; col++) {
rowJoiner.add(Integer.toString(col).repeat(row));
}
textJoiner.add(rowJoiner.toString());
}
setLayout(new BorderLayout());
JTextArea ta = new JTextArea(10, 40);
ta.setFont(new Font("Monospaced", Font.PLAIN, 13));
ta.setText(textJoiner.toString());
add(new JScrollPane(ta));
}
protected String replicate(char value, int times) {
return new String(new char[times]).replace('\0', value);
}
}
}
I think you're thinking of "tab stops", rather than "tab size", for example, in which case, even the DocumentFilter won't do what you're expecting.
I assume the use of monospace font is implied in the question
Don't "assume" we know anything. In my experimentation, the font was NOT monospaced. This is where providing "expected" and "actual" results and a minimal reproducible example, as it removes the ambiguity and doesn't waste everybody's time (especially yours)
It is how it works in any text editor.
I'm obviously using different text editors
