jbutton鼠标放上去显示说明怎么实现啊？

有这个方法
JButton button=new JButton();
button.setToolTipText("this is a tip");

//运行下吧~
import javax.swing.JButton;
import javax.swing.JFrame;

public class TipTest extends JFrame {

private static final long serialVersionUID = 5638996572665148343L;
JButton b = new JButton("移动鼠标到我");
public void init(){
this.setLayout(null);
b.setBounds(50, 50, 150, 25);
b.setToolTipText("我知道了");//here
this.add(b);
this.setBounds(200, 200, 400, 300);
this.setResizable(false);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setVisible(true);
}

public static void main(String[] args) {
new TipTest().init();
}

}