在java中怎样把文本区域里的内容保存成txt格式的文件

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextArea;

public class Test extends JFrame {

private static final long serialVersionUID = 1L;
private JTextArea txtArea;

private BufferedWriter buf;

public static void main(String args[]) {
try {
Test frame = new Test();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}

public Test() {
super();
getContentPane().setLayout(null);
setName("frame");
setResizable(false);
setTitle("Test");
setBounds(100, 100, 300, 300);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

txtArea = new JTextArea();