java中JTextfield怎样使它有提示内容，就是文本框默认有内容，鼠标点进去内容消失这样的

package com;import java.awt.FlowLayout;import java.awt.event.FocusAdapter;import java.awt.event.FocusEvent;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JTextField;public class Kyo extends JFrame{ public Kyo() { setSize(100,100)