How to change text color in the JTextArea?

since is possible use Highlighter (or Html) for JTextArea, this API implementing reduced options for stylled text

import java.awt.*;
import javax.swing.*;
import javax.swing.text.*;

public class TextPaneHighlighting {

    private static final long serialVersionUID = 1L;
    private Highlighter.HighlightPainter cyanPainter;
    private Highlighter.HighlightPainter redPainter;

    public TextPaneHighlighting() {
        JFrame frame = new JFrame();
        JTextPane textPane = new JTextPane();
        textPane.setText("one\ntwo\nthree\nfour\nfive\nsix\nseven\neight\n");
        JScrollPane scrollPane = new JScrollPane(textPane);
        frame.add(scrollPane, BorderLayout.CENTER);//  Highlight some text
        cyanPainter = new DefaultHighlighter.DefaultHighlightPainter(Color.cyan);
        redPainter = new DefaultHighlighter.DefaultHighlightPainter(Color.red);
        try {
            textPane.getHighlighter().addHighlight(0, 3, DefaultHighlighter.DefaultPainter);
            textPane.getHighlighter().addHighlight(8, 14, cyanPainter);
            textPane.getHighlighter().addHighlight(19, 24, redPainter);
        } catch (BadLocationException ble) {
        }
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(300, 200));
        frame.setLocationRelativeTo(null);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                TextPaneHighlighting tph = new TextPaneHighlighting();
            }
        });
    }
}

in compare with JTextPane there is options more variable, e.g. Highlighter, with Html or without Html, Font, or put another JComponent inside by using Html or directly (know JTextArea too, but...)

import java.awt.*;
import javax.swing.*;
import javax.swing.text.*;

public class Fonts implements Runnable {

    private String[] fnt;
    private JFrame frm;
    private JScrollPane jsp;
    private JTextPane jta;
    private int width = 450;
    private int height = 300;
    private GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
    private StyledDocument doc;
    private MutableAttributeSet mas;
    private int cp = 0;
    private Highlighter.HighlightPainter cyanPainter = new DefaultHighlighter.DefaultHighlightPainter(Color.cyan);
    private Highlighter.HighlightPainter redPainter = new DefaultHighlighter.DefaultHighlightPainter(Color.red);
    private Highlighter.HighlightPainter whitePainter = new DefaultHighlighter.DefaultHighlightPainter(Color.white);
    private int _count = 0;
    private int _lenght = 0;

    public Fonts() {
        jta = new JTextPane();
        doc = jta.getStyledDocument();
        jsp = new JScrollPane(jta);
        jsp.setPreferredSize(new Dimension(height, width));
        frm = new JFrame("awesome");
        frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frm.setLayout(new BorderLayout());
        frm.add(jsp, BorderLayout.CENTER);
        frm.setLocation(100, 100);
        frm.pack();
        frm.setVisible(true);
        jta.setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
        fnt = ge.getAvailableFontFamilyNames();
        mas = jta.getInputAttributes();
        new Thread(this).start();
    }

    @Override
    public void run() {
        for (int i = 0; i < fnt.length; i++) {
            StyleConstants.setBold(mas, false);
            StyleConstants.setItalic(mas, false);
            StyleConstants.setFontFamily(mas, fnt[i]);
            StyleConstants.setFontSize(mas, 16);
            dis(fnt[i]);
            try {
                Thread.sleep(75);
            } catch (Exception e) {
                e.printStackTrace();
            }
            StyleConstants.setBold(mas, true);
            dis(fnt[i] + " Bold");
            try {
                Thread.sleep(75);
            } catch (Exception e) {
                e.printStackTrace();
            }
            StyleConstants.setItalic(mas, true);
            dis(fnt[i] + " Bold & Italic");
            try {
                Thread.sleep(75);
            } catch (Exception e) {
                e.printStackTrace();
            }
            StyleConstants.setBold(mas, false);
            dis(fnt[i] + " Italic");
            try {
                Thread.sleep(75);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        jta.setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
    }

    public void dis(String s) {
        _count++;
        _lenght = jta.getText().length();
        try {
            doc.insertString(cp, s, mas);
            doc.insertString(cp, "\n", mas);
        } catch (Exception bla_bla_bla_bla) {
            bla_bla_bla_bla.printStackTrace();
        }
        if (_count % 2 == 0) {
            try {
                jta.getHighlighter().addHighlight(1, _lenght - 1, cyanPainter);
            } catch (BadLocationException bla_bla_bla_bla) {
            }
        } else if (_count % 3 == 0) {
            try {
                jta.getHighlighter().addHighlight(1, _lenght - 1, redPainter);
            } catch (BadLocationException bla_bla_bla_bla) {
            }
        } else {
            try {
                jta.getHighlighter().addHighlight(1, _lenght - 1, whitePainter);
            } catch (BadLocationException bla_bla_bla_bla) {
            }
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                Fonts fs = new Fonts();
            }
        });
    }
}

JTextArea is meant to entertain Plain Text. The settings applied to a single character applies to whole of the document in JTextArea. But with JTextPane or JEditorPane you have the choice, to colour your String Literals as per your liking. Here with the help of JTextPane, you can do it like this :

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

import javax.swing.border.*;

import javax.swing.text.AttributeSet;
import javax.swing.text.SimpleAttributeSet;
import javax.swing.text.StyleConstants;
import javax.swing.text.StyleContext;

public class TextPaneTest extends JFrame
{
    private JPanel topPanel;
    private JTextPane tPane;

    public TextPaneTest()
    {
        topPanel = new JPanel();        

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);            

        EmptyBorder eb = new EmptyBorder(new Insets(10, 10, 10, 10));

        tPane = new JTextPane();                
        tPane.setBorder(eb);
        //tPane.setBorder(BorderFactory.createLineBorder(Color.DARK_GRAY));
        tPane.setMargin(new Insets(5, 5, 5, 5));

        topPanel.add(tPane);

        appendToPane(tPane, "My Name is Too Good.\n", Color.RED);
        appendToPane(tPane, "I wish I could be ONE of THE BEST on ", Color.BLUE);
        appendToPane(tPane, "Stack", Color.DARK_GRAY);
        appendToPane(tPane, "Over", Color.MAGENTA);
        appendToPane(tPane, "flow", Color.ORANGE);

        getContentPane().add(topPanel);

        pack();
        setVisible(true);   
    }

    private void appendToPane(JTextPane tp, String msg, Color c)
    {
        StyleContext sc = StyleContext.getDefaultStyleContext();
        AttributeSet aset = sc.addAttribute(SimpleAttributeSet.EMPTY, StyleConstants.Foreground, c);

        aset = sc.addAttribute(aset, StyleConstants.FontFamily, "Lucida Console");
        aset = sc.addAttribute(aset, StyleConstants.Alignment, StyleConstants.ALIGN_JUSTIFIED);

        int len = tp.getDocument().getLength();
        tp.setCaretPosition(len);
        tp.setCharacterAttributes(aset, false);
        tp.replaceSelection(msg);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
            {
                public void run()
                {
                    new TextPaneTest();
                }
            });
    }
}

here is the Output :