Develop Reference

How can I replace a tab with four spaces in JTextArea?

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();
}
}
}
}
}
Admittable limitations
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)
More investigations
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
I'm obviously missing something...
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 🤪

Java Swing TextArea: How to simultaneously print Transliterated text/s in an Output TextArea?

I am trying to write a text editor. I want two TextAreas: 1st one for typing/editing in unicode script and 2nd one for simultaneously printing output of the unicode script input in corresponding Roman Script (ASCII) set by myself on the basis of a transliteration scheme.
I am not able to update and simultaneously print the input text in output textarea while I call the transliteration method. I can sense a little bit that there is something wrong while I set the output textArea to print simultaneously but I am unable to find out what exactly is that.
The Editor class------->
import java.awt.*;
import java.beans.PropertyChangeSupport;
import javax.swing.*;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
public class editor extends JPanel {
private static final int ROWS = 10;
private static final int COLS = 50;
private static final String[] BUTTON_NAMES = {"विविधाः", "द्वाराणि", "Setting", "Parse", "Compile"};
private static final int GAP = 3;
private JTextArea inputTextArea = new JTextArea(ROWS, COLS);
private JTextArea outputTextArea = new JTextArea(ROWS, COLS);
private JTextArea TA = new JTextArea(ROWS, COLS);
//calling the transliteration method
transliterator tr = new transliterator();
Document asciiDocument=tr.DevanagariTransliteration(inputTextArea.getDocument());
public editor() throws BadLocationException {
JPanel buttonPanel = new JPanel(new GridLayout(1, 0, GAP, 0));
for (String btnName : BUTTON_NAMES) {
buttonPanel.add(new JButton(btnName));
}
setBorder(BorderFactory.createEmptyBorder(GAP, GAP, GAP, GAP));
setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
add(buttonPanel);
add(putInTitledScrollPane(inputTextArea, "देवनागरी <<<<<<>>>>>> Devanagari"));
inputTextArea.setFocusable(true);
outputTextArea.setFocusable(false);
outputTextArea.setEditable(false);
//String inputCheck = inputTextArea.getText();
//inputTextArea.setText("x");
//if (inputTextArea.getText().length()>0) {
outputTextArea.setDocument(asciiDocument);//printing input in 2nd textarea
// outputTextArea.setDocument(inputTextArea.getDocument());//printing input in 2nd textarea
add(putInTitledScrollPane(outputTextArea, "IndicASCII"));
}
private JPanel putInTitledScrollPane(JComponent component,
String title) {
JPanel wrapperPanel = new JPanel(new BorderLayout());
wrapperPanel.setBorder(BorderFactory.createTitledBorder(title));
wrapperPanel.add(new JScrollPane(component));
return wrapperPanel;
}
private static void createAndShowGui() throws BadLocationException {
editor mainPanel = new editor();
JFrame frame = new JFrame("Unicode Editor");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
ImageIcon imgicon = new ImageIcon("MyIcon.jpg");
frame.setIconImage(imgicon.getImage());
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
try {
createAndShowGui();
} catch (BadLocationException e) {
e.printStackTrace();
}
}
});
}
}
And transliteration class method:
import javax.swing.*;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
public class transliterator {
//method that returns a Document type
// the method - importing devanagari text through the type 'Document' from input textArea by call
public Document DevanagariTransliteration(Document devanagariTextDocument) throws BadLocationException {
//extracting the devanagari text from the imported Document type
String asciiText = devanagariTextDocument.getText(0, devanagariTextDocument.getLength());
//devanagari unicode a replaced by ascii a
String transliteratedText = asciiText.replace('\u0905', 'a');
JTextArea jt = new JTextArea();
//inserting the TRANSLITERATED text to a textArea to extract as a Document again
jt.setText(transliteratedText);
//extracting and creating as a document
Document ASCIITextDocument = jt.getDocument();
//returning the document
return ASCIITextDocument;
}
}

To reflect changes in one document onto another document you can use a DocumentListener as suggested by camickr.
The following is an mre that demonstrates updating the "output" JTextArea after processing the changes in the "input" JTextArea.
The processing used for demonstration purposes is a simply converting the input to upper case. This should be changed to your specific needs :
import java.awt.BorderLayout;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
public class MyWindow extends JPanel {
private static final int ROWS = 10, COLS = 50;
private final JTextArea outputTextArea;
public MyWindow() {
setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
JTextArea inputTextArea = new JTextArea(ROWS, COLS);
inputTextArea.getDocument().addDocumentListener(new TransliterateDocumentListener());
add(putInTitledScrollPane(inputTextArea,"Input"));
outputTextArea = new JTextArea(ROWS, COLS);
outputTextArea.setFocusable(false);
outputTextArea.setEditable(false);
add(putInTitledScrollPane(outputTextArea, "Output"));
}
private JPanel putInTitledScrollPane(JComponent component, String title) {
JPanel wrapperPanel = new JPanel(new BorderLayout());
wrapperPanel.setBorder(BorderFactory.createTitledBorder(title));
wrapperPanel.add(new JScrollPane(component));
return wrapperPanel;
}
private static void createAndShowGui() {
JFrame frame = new JFrame("Document Listener Demo");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().add( new MyWindow());
frame.pack();
frame.setVisible(true);
}
private void insert(String text, int from) {
text = process(text);
try {
outputTextArea.getDocument().insertString(from, text, null);
} catch (BadLocationException ex) {
ex.printStackTrace();
}
}
private void remove(int from, int length) {
try {
outputTextArea.getDocument().remove(from, length);
} catch (BadLocationException ex) {
ex.printStackTrace();
}
}
private String process(String text) {
//todo process text as needed
//returns upper case text for demo
return text.toUpperCase();
}
class TransliterateDocumentListener implements DocumentListener {
#Override
public void insertUpdate(DocumentEvent e) {
Document doc = e.getDocument();
int from = e.getOffset(), length = e.getLength();
try {
insert(doc.getText(from, length), from);
} catch (BadLocationException ex) {
ex.printStackTrace();
}
}
#Override
public void removeUpdate(DocumentEvent e) {
remove(e.getOffset(), e.getLength());
}
#Override
public void changedUpdate(DocumentEvent e) {
//Plain text components don't fire these events.
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
}

When I used the setDocument() method I cannot handle the text input
All the setDocument() method does is share the Document between multiple components. So whatever you type will be displayed in both components.
Instead you would use a DocumentListener. The listener will generate an event whenever text is added or removed from the Document. Then you will need to read the text from the Document and do your translation and update the second text area.
See the section from the Swing tutorial on How to Write a DocumentListener for the basics to get you started.

Java Swing JTextArea Line number

This count line number of textarea. The code works correctly, but when run this code the textarea is not active, the caret is hidden and the keyboard
keys not work unless I click on textarea.
code:
import java.awt.BorderLayout;
import java.awt.Color;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.Element;
public class LineNumber extends JFrame implements DocumentListener {
private static final long serialVersionUID = -1093726028044203117L;
private JScrollPane scroll;
private JTextArea textArea, lineArea;
public static void main(String[] args) {
new LineNumber().setVisible(true);
}
public LineNumber() {
super("Line Numbers");
setSize(500, 500);
setLocationRelativeTo(null);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setUI();
}
private void setUI() {
textArea = new JTextArea();
lineArea = new JTextArea(0, 3);
lineArea.setEditable(false);
lineArea.setForeground(Color.GRAY);
scroll = new JScrollPane(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
textArea.getDocument().addDocumentListener(this);
scroll.setViewportView(textArea);
scroll.setRowHeaderView(lineArea);
getContentPane().add(scroll, BorderLayout.CENTER);
}
public void changedUpdate(DocumentEvent event) {
lineArea.setFont(textArea.getFont());
lineArea.setText(getLine());
}
public void insertUpdate(DocumentEvent event) {
lineArea.setFont(textArea.getFont());
lineArea.setText(getLine());
}
public void removeUpdate(DocumentEvent event) {
lineArea.setFont(textArea.getFont());
lineArea.setText(getLine());
}
public String getLine() {
int caretPos = 0;
String lines;
caretPos = textArea.getDocument().getLength();
Element root = textArea.getDocument().getDefaultRootElement();
lines = String.format("%s%s", 1, System.lineSeparator());
for (int i = 2; i < root.getElementIndex(caretPos) + 2; i++) {
lines += String.format("%s%s", i, System.lineSeparator());
}
return lines;
}
}
If I do not add lineArea to the scrollpane the textarea work correctly but after add to setRowHeaderView the textarea only gets active with a mouse click....

You can prevent the line number text area from gaining focus by using:
lineArea = new JTextArea(0, 3);
lineArea.setEditable(false);
lineArea.setFocusable(false);
You can also check out Text Component Line Number for a fancier implementation that supports:
wrapped text
text with different size fonts (when using a JTextPane)

By default it focus on first component, so if you want to focus on another one try this code in the constructor.
addWindowFocusListener(new WindowAdapter() {
#Override
public void windowGainedFocus(WindowEvent e) {
textArea.requestFocusInWindow();
}
});
textArea is now focused, more on this.

jTextArea stops showing highlighting on text after losing focus

When my jTextArea is in focus it allows text highlighting, but it doesn't show the text selection when it loses focus. Is it possible to continue displaying the text highlighting even if the user moves focus to another component on the related jFrame?

One simple workaround for caret selection is a simple subclassing of DefaultCaret:
textArea.setCaret(new DefaultCaret() {
#Override
public void setSelectionVisible(boolean visible) {
super.setSelectionVisible(true);
}
});

but doesn't show selection on text when looses focus.
there are three ways:
use JTextPane, see Oracle tutorial
easiest in the case that we talking about selection as painting artefact from Mouse Event see my question How to override DefaultCaret#setBlinkRate(), great knowledge and answer by #camickr
or programatically override Highlighter
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.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.text.BadLocationException;
import javax.swing.text.DefaultHighlighter;
import javax.swing.text.Highlighter;
import javax.swing.text.JTextComponent;
public class MultiHighlight implements ActionListener {
private JTextComponent comp;
private String charsToHighlight;
public MultiHighlight(JTextComponent c, String chars) {
comp = c;
charsToHighlight = chars;
}
#Override
public void actionPerformed(ActionEvent e) {
Highlighter h = comp.getHighlighter();
h.removeAllHighlights();
String text = comp.getText().toUpperCase();
for (int j = 0; j < text.length(); j += 1) {
char ch = text.charAt(j);
if (charsToHighlight.indexOf(ch) >= 0) {
try {
h.addHighlight(j, j + 1, DefaultHighlighter.DefaultPainter);
} catch (BadLocationException ble) {
}
}
}
}
public static void main(String args[]) {
final JFrame frame = new JFrame("MultiHighlight");
frame.add(new JTextField("Another focusable JComponents"), BorderLayout.NORTH);
JTextArea area = new JTextArea(10, 20);
area.setText("This is the story\nof the hare who\nlost his spectacles."
+ "\nThis is the story\nof the hare who\nlost his spectacles.");
frame.getContentPane().add(new JScrollPane(area), BorderLayout.CENTER);
JButton b = new JButton("Highlight All Vowels");
b.addActionListener(new MultiHighlight(area, "aeiouAEIOU"));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(b, BorderLayout.SOUTH);
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
frame.pack();
frame.setVisible(true);
}
});
}
}

How to extract the word and line wrapping information from JTextArea for text with given font

I have to convert styled text to wrapped simple text (for SVG word wrapping). I cannot beleive that the word wrapping information (how many lines are there, where are the line breaks) cannot be extracted from the JTextArea. So I created a small frame program:
package bla;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.Frame;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JTextArea;
public class Example1 extends WindowAdapter {
private static String content = "01234567890123456789\n" + "0123456 0123456 01234567 01234567";
JTextArea text;
public Example1() {
Frame f = new Frame("TextArea Example");
f.setLayout(new BorderLayout());
Font font = new Font("Serif", Font.ITALIC, 20);
text = new JTextArea();
text.setFont(font);
text.setForeground(Color.blue);
text.setLineWrap(true);
text.setWrapStyleWord(true);
f.add(text, BorderLayout.CENTER);
text.setText(content);
// Listen for the user to click the frame's close box
f.addWindowListener(this);
f.setSize(100, 511);
f.show();
}
public static List<String> getLines( JTextArea text ) {
//WHAT SHOULD I WRITE HERE
return new ArrayList<String>();
}
public void windowClosing(WindowEvent evt) {
List<String> lines = getLines(text);
System.out.println( "Number of lines:" + lines.size());
for (String line : lines) {
System.out.println( line );
}
System.exit(0);
}
public static void main(String[] args) {
Example1 instance = new Example1();
}
}
If you run it you will see this:
And what I expect as output:
Number of lines:6
0123456789
0123456789
0123456
0123456
01234567
01234567
What should I write in place of the comment?
Complete answer:
So, then the complete solution based on the accepted answer without displaying the frame actually (note, that you should remove the actual newline characters from the result):
package bla;
import java.awt.Color;
import java.awt.Font;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JTextArea;
import javax.swing.text.BadLocationException;
import javax.swing.text.Utilities;
public class Example1 {
private static String content = "01234567890123456789\n" + "0123456 0123456 01234567 01234567";
public static List<String> getLines( String textContent, int width, Font font ) throws BadLocationException {
JTextArea text;
text = new JTextArea();
text.setFont(font);
text.setForeground(Color.blue);
text.setLineWrap(true);
text.setWrapStyleWord(true);
text.setText(content);
text.setSize(width, 1);
int lastIndex = 0;
int index = Utilities.getRowEnd(text, 0);
List<String> result = new ArrayList<String>();
do {
result.add( textContent.substring( lastIndex, Math.min( index+1, textContent.length() ) ) );
lastIndex = index + 1;
}
while ( lastIndex < textContent.length() && ( index = Utilities.getRowEnd(text, lastIndex) ) > 0 );
return result;
}
public static void main(String[] args) throws BadLocationException {
Font font = new Font("Serif", Font.ITALIC, 20);
Example1 instance = new Example1();
for (String line : getLines(content,110,font)) {
System.out.println( line.replaceAll( "\n", "") );
}
}
}
Open question in me (not that important), why is that a frame with 100px width containing a jtextarea wraps the text later than a jtextarea without frame with the same width. Ideas for this?

JTextArea does not support styled text, but it does support line-oriented access to its model, PlainDocument, as shown below. For reference,
Don't mix AWT (Frame) and Swing (JTextArea) components unnecessarily.
Swing GUI objects should be constructed and manipulated only on the event dispatch thread.
As noted here, the getLineCount() method counts line.separator delimited lines, not wrapped lines.
BasicTextUI handles Look & Feel dependent rendering; the methods viewToModel() and viewToModel() translate between the two coordinate systems.
Console:
01234567890123456789
0123456 0123456
01234567 01234567
Code:
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;
public class Example2 {
private static final Character SEP = Character.LINE_SEPARATOR;
private static String content = ""
+ "01234567890123456789" + SEP
+ "0123456 0123456" + SEP
+ "01234567 01234567";
private JTextArea text;
public Example2() {
JFrame f = new JFrame("TextArea Example");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Font font = new Font("Serif", Font.ITALIC, 20);
text = new JTextArea(4, 8);
text.setFont(font);
text.setForeground(Color.blue);
text.setLineWrap(true);
text.setWrapStyleWord(true);
text.setText(content);
f.add(new JScrollPane(text));
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
for (String s : getLines(text)) {
System.out.println(s);
}
}
private List<String> getLines(JTextArea text) {
PlainDocument doc = (PlainDocument) text.getDocument();
List<String> list = new ArrayList<String>();
for (int i = 0; i < text.getLineCount(); i++) {
try {
int start = text.getLineStartOffset(i);
int length = text.getLineEndOffset(i) - start;
list.add(doc.getText(start, length));
} catch (BadLocationException ex) {
ex.printStackTrace(System.err);
}
}
return list;
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
Example2 instance = new Example2();
}
});
}
}

Use Utilities.getRowEnd()
Pass 0 as start offset and then previousline's end offset +1

JTextArea does have a : getLines() method, is that not working for you?