我的JScrollPane怎么了，求助

[bbrr]

Java的awt和swing组件的范例程序，我照做了二十二个都全顺利运行，可是到了JScrollPane的时候，不知道错在哪，请前辈耐心指教，代码如下：

import java.awt.*;
import javax.swing.*;
public class JScrollPaneExample
{
public static void main(String args[])
{
JTextArea jta=new JTextArea();
int v_scrollbar=ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
int h_scrollbar=ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;
JScrollPane jsp=new JScrollPane(jta,v_scrollbar,h_scrollbar);
JButton jb1=new JButton("我是按钮");
JButton jb2=new JButton("me too!");
jsp.setColumnHeaderView(jb1);
jsp.setRowHeaderView(jb2);
JPanel jp1=new JPanel();
JPanel jp2=new JPanel();
JPanel jp3=new JPanel();
jp1.setBackground(Color.green);
jp2.add(new JCheckBox("选我"));
jsp.setCorner(JScrollPane.UPPER_RIGHT_CORNER,jp2);
jsp.setCorner(JScrollPane.UPPER_LEFT_CORNER,jp3);
jsp.setCorner(JScrollPane.LOWER_LEFT_CORNER,jp3);
JFrame jf=new JFrame("使用JScrollPane组件");
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jf.getContentPane().add(jsp);
jf.setBounds(0,0,250,200);
jf.setVisible(true);
}
}

编译时的捕捉到的错误如下：

JScrollPaneExample.java:10: cannot resolve symbol
symbol : constructor JScrollPane (javax.swing.JTextArea,int,int)
location: class JScrollPane
JScrollPane jsp=new JScrollPane(jta,v_scrollbar,h_scrollbar);
^
JScrollPaneExample.java:13: cannot resolve symbol
symbol : method setColumnHeaderView (javax.swing.JButton)
location: class JScrollPane
jsp.setColumnHeaderView(jb1);
^
JScrollPaneExample.java:14: cannot resolve symbol
symbol : method setRowHeaderView (javax.swing.JButton)
location: class JScrollPane
jsp.setRowHeaderView(jb2);
^
JScrollPaneExample.java:20: cannot resolve symbol
symbol : variable UPPER_RIGHT_CORNER
location: class JScrollPane
jsp.setCorner(JScrollPane.UPPER_RIGHT_CORNER,jp2);
^
JScrollPaneExample.java:21: cannot resolve symbol
symbol : variable UPPER_LEFT_CORNER
location: class JScrollPane
jsp.setCorner(JScrollPane.UPPER_LEFT_CORNER,jp3);
^
JScrollPaneExample.java:22: cannot resolve symbol
symbol : variable LOWER_LEFT_CORNER
location: class JScrollPane
jsp.setCorner(JScrollPane.LOWER_LEFT_CORNER,jp3);
^
JScrollPaneExample.java:25: cannot resolve symbol
symbol : method add (JScrollPane)
location: class java.awt.Container
jf.getContentPane().add(jsp);
^
.\JScrollPane.java:10: cannot resolve symbol
symbol : constructor JScrollPane (javax.swing.JTextArea,int,int)
location: class JScrollPane
JScrollPane jsp=new JScrollPane(jta,v_scrollbar,h_scrollbar);
^
.\JScrollPane.java:13: cannot resolve symbol
symbol : method setColumnHeaderView (javax.swing.JButton)
location: class JScrollPane
jsp.setColumnHeaderView(jb1);
^
.\JScrollPane.java:14: cannot resolve symbol
symbol : method setRowHeaderView (javax.swing.JButton)
location: class JScrollPane
jsp.setRowHeaderView(jb2);
^
.\JScrollPane.java:20: cannot resolve symbol
symbol : variable UPPER_RIGHT_CORNER
location: class JScrollPane
jsp.setCorner(JScrollPane.UPPER_RIGHT_CORNER,jp2);
^
.\JScrollPane.java:21: cannot resolve symbol
symbol : variable UPPER_LEFT_CORNER
location: class JScrollPane
jsp.setCorner(JScrollPane.UPPER_LEFT_CORNER,jp3);
^
.\JScrollPane.java:22: cannot resolve symbol
symbol : variable LOWER_LEFT_CORNER
location: class JScrollPane
jsp.setCorner(JScrollPane.LOWER_LEFT_CORNER,jp3);
^
.\JScrollPane.java:25: cannot resolve symbol
symbol : method add (JScrollPane)
location: class java.awt.Container
jf.getContentPane().add(jsp);
^
14 errors

[bbrr]

没有问题呀，有时候明明没错却提示错误，把所有窗口关掉重新打开就正常了

[Lucy222]

9494，把分数给我吧