When JTextArea.setWrapStyleWord() is set to false, which is by default, it does not wrap supplementary characters properly. With the attached example, it appears that the high and lo surrogate gets separated as separate characters when doing the character wrap.

Once you've launched the application, resize the width of the window until you see 2 square boxes, one on the one line and the other in the next. It's assumed that this indicates that JTextArea is treating the high and lo surrogates as separate characters rather than as one.

This may be related to bug# 4904691, however, line wrapping is specific to JTextArea so it may be a different problem.

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

public class SupplementaryTest extends JFrame {

    JTextArea textArea;
    JScrollPane scrollPane;
    JPanel panel;

    public static void main(String[] args) {
        String s = "hello there world I am the best dri\\uD800\\uDFFFer period";
        new SupplementaryTest(processLine(s));
    }

    public SupplementaryTest(String text) {
        textArea = new JTextArea(text, 5, 5);
        textArea.setLineWrap(true);

        setContentPane(textArea);
        pack();
        show();
    }

    private static String processLine(String line) {
        int index = 0;

        // Process UTF-16 characters until there are no more.
        while ((index = line.indexOf("\\u")) != -1) {
            StringBuffer temp = new StringBuffer(line);
            String value = temp.substring(index+2, index+6);
            char aChar = (char)Integer.parseInt(value, 16);
            String unicodeChar = "" + aChar;
            temp.replace(index, index+6, unicodeChar);
            line = temp.toString();
        }

        return line;
    }
}
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