JavaでJOptionPaneメッセージダイアログの長いテキストを実装するにはどうすればよいですか？

例

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class JOptionPaneScrollTextMessage extends JFrame {
   private JButton btn;
   String msg;
   public JOptionPaneScrollTextMessage() {
      setTitle("JOptionPaneScrollTextMessage Test");
      msg = " Java is a programming language that produces software for multiple platforms.\n When a       programmer writes a Java application, the compiled code\n" + "(known as bytecode) runs on most       operating systems (OS), including \n Windows, Linux and Mac OS. Java derives much of its syntax       \n from the C and C++" + "programming languages.\n Java was developed in the mid-1990s by James       A. Gosling, a former computer scientist with Sun Microsystems.";
      btn = new JButton("Show Dialog");
      btn.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent ae) {
            JTextArea jta = new JTextArea(5, 15);
            jta.setText(msg);
            jta.setEditable(false);
            JScrollPane jsp = new JScrollPane(jta);
            JOptionPane.showMessageDialog(null, jsp);
         }
      });
      add(btn, BorderLayout.NORTH);
      setSize(400, 300);
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setLocationRelativeTo(null);
      setVisible(true);
   }
   public static void main(String[] args) {
      new JOptionPaneScrollTextMessage();
   }
}