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A commonly asked question is how to display text in multiple colors or styles within a JTextArea component. The short answer is: you can't. Both the JTextField and JTextArea components are designed to display text in a single style, color, font. When you change the characteristics of the text, you are changing all text in the component. You can't change the characteristics of only the selected text, or just the piece you want changed.
Just because the JTextArea component can't display its content in multiple colors or styles, doesn't mean there isn't support for displaying text in multiple styles. It just isn't done with the JTextArea. You need to use the JTextPane. Knowing that it is the JTextPane and not the JTextArea will lead you to the actual "how" answer to the original question.
Within the JTextPane, text that you add to the component is associated with an AttributeSet. The AttributeSet contains a set of key-value pairs for the various display attributes of the text. These pairs can answer questions like "what's the current font?", "what's the background color?", and "with what alignment should I display the current paragraph?" By setting this AttributeSet before adding the text, you can change the way the added text is displayed. You can also change the AttributeSet for the currently selected text.
AttributeSet is an interface in the javax.swing.text package. To fill the set with the desired characteristics, you need to work with an implementation of that interface. That implementation is most likely SimpleAttributeSet, though it can also be StyleContext.SmallAttributeSet or StyleContext.NamedStyle.
SimpleAttributeSet set = new SimpleAttributeSet();
After you create the set, you set the attributes, but this involves a little complexity. The possible settings for the different styles are found in the inner classes of the StyleConstants class:
CharacterConstants
ColorConstants
FontConstants
ParagraphConstants
Each of these inner classes has a set of constants for each of its supported attributes:
CharacterConstants
- Background
- BidiLevel
- Bold
- ComponentAttribute
- Family
- Foreground
- IconAttribute
- Italic
- Size
- StrikeThrough
- Subscript
- Superscript
- Underline
ColorConstants
- Background
- Foreground
FontConstants
- Bold
- Family
- Italic
- Size
ParagraphConstants
- Alignment
- FirstLineIndent
- LeftIndent
- LineSpacing
- Orientation
- RightIndent
- SpaceAbove
- SpaceBelow
- TabSet
To change the set of attributes for newly-added text, you add the necessary attribute to an AttributeSet, and associate the set with the JTextPane. You can also replace the existing set, or as previously mentioned, change the attributes for the current text selection.
SimpleAttributeSet set = new SimpleAttributeSet();
set.addAttribute(
StyleConstants.CharacterConstants.Bold,
Boolean.TRUE);
JTextPane tp = new JTextPane();
// false = don't replace attribute for all text
tp.setCharacterAttributes(set, false);
In addition to using addAttribute to add attributes to the set, there are some helper methods in the StyleConstants class. For instance, instead of having to use StyleConstants.CharacterConstants.Bold, as shown above, you can simply call the setBold method of StyleConstants, and pass in the appropriate AttributeSet and boolean value:
StyleConstants.setBold(set, true);
Actually, the first argument to the StyleConstants methods must be a MutableAttributeSet, which is an extension of the AttributeSet interface. SimpleAttributeSet implements both MutableAttributeSet and AttributeSet. See the StyleConstants class definition for the full set of methods.
Because the setText method of JTextPane will replace all the content, a better way to add multi-attributed text is to work with the component's Document, which contains the text and its attributes. Get the Document with getStyledDocument, and add text to it with insertString. The insertString method requires as arguments, the position to add, the text to add, and the attribute set. The method can also throw a BadLocationException, which you must catch or pass along.
Document doc = pane.getStyledDocument();
try {
doc.insertString(doc.getLength(), "Blind", set);
} catch (BadLocationException e) {
System.err.println("Bad location");
return;
}
To demonstrate, let's provide a JTextPane with three words, where each word has a different style. Notice the different ways the attribute sets are initialized and associated with the JTextPane.
import java.awt.*;
import javax.swing.*;
import javax.swing.text.*;
public class Multi {
public static void main(String args[]) {
JFrame frame = new JFrame(
"Multiattributed text");
frame.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE);
Container content = frame.getContentPane();
JTextPane pane = new JTextPane();
SimpleAttributeSet set =
new SimpleAttributeSet();
set.addAttribute(
StyleConstants.CharacterConstants.Bold,
Boolean.TRUE);
// Initialize attributes before adding text
pane.setCharacterAttributes(set, true);
pane.setText("Three");
set = new SimpleAttributeSet();
StyleConstants.setItalic(set, true);
StyleConstants.setForeground(set, Color.PINK);
StyleConstants.setBackground(set, Color.GREEN);
Document doc = pane.getStyledDocument();
try {
doc.insertString(
doc.getLength(), "Blind", set);
} catch (BadLocationException e) {
System.err.println("Bad location");
return;
}
set = new SimpleAttributeSet();
StyleConstants.setFontSize(set, 48);
try {
doc.insertString(
doc.getLength(), "Mice", set);
} catch (BadLocationException e) {
System.err.println("Bad location");
return;
}
JScrollPane scrollPane = new JScrollPane(pane);
content.add(scrollPane, BorderLayout.CENTER);
frame.setSize(300, 200);
frame.show();
}
}
When you run the program, here's what you should see:
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