是哪里出了问题

Question

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.plaf.basic.BasicArrowButton;public class ButtonsDemo extends JFrame
{
private JButton jb = new JButton("JButton");
private BasicArrowButton up = new BasicArrowButton(BasicArrowButton.NORTH)
down = new BasicArrowButton(BasicArrowButton.SOUTH);
right = new BasicArrowButton(BasicArrowButton.EAST);
left = new BasicArrowButton(BasicArrowButton.WEST);

public ButtonsDemo(String title)
{
super(title);
Container contentPane = getContentPane();
contentPane.setLayout(new FlowLayout());
contentPane.add(jb);
contentPane.add(new JToggleButton("JToggleButton"));
contentPane.add(new JCheckBox("JCheckBox"));
contentPane.add(new JRadioButton("JRadioButton"));
JPanel jp = new JPanel();
jp.setBorder(new TitledBorder("Directions"));
jp.add(up);
jp.add(down);
jp.add(left);
jp.add(right);
contentPane.add(jp);

pack();
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}
public static void main(String[] args)
{
new ButtonsDemo("Hello");
}
}报错：Exception in thread "main" java.lang.Error: Unresolved compilation problem:  at ButtonsDemo.main(ButtonsDemo.java:38)

Answer 1

private BasicArrowButton up = new BasicArrowButton(BasicArrowButton.NORTH) ；

Answer 2

楼上指出了一个错误。
down = new BasicArrowButton(BasicArrowButton.SOUTH);
right = new BasicArrowButton(BasicArrowButton.EAST);
left = new BasicArrowButton(BasicArrowButton.WEST); 
三个变量也没有定义。

Answer 3

import java.awt.*; 
import java.awt.event.*; 
import java.util.*; 
import javax.swing.*; 
import javax.swing.border.Border; 
import javax.swing.border.TitledBorder;
import javax.swing.plaf.basic.BasicArrowButton; public class ButtonDemo extends JFrame 
{ 
private JButton jb = new JButton("JButton"); 
private BasicArrowButton up = new BasicArrowButton(BasicArrowButton.NORTH), 
down = new BasicArrowButton(BasicArrowButton.SOUTH), 
right = new BasicArrowButton(BasicArrowButton.EAST), 
left = new BasicArrowButton(BasicArrowButton.WEST); public ButtonDemo(String title) 
{ 
super(title); 
Container contentPane = getContentPane(); 
contentPane.setLayout(new FlowLayout()); 
contentPane.add(jb); 
contentPane.add(new JToggleButton("JToggleButton")); 
contentPane.add(new JCheckBox("JCheckBox")); 
contentPane.add(new JRadioButton("JRadioButton")); 
JPanel jp = new JPanel(); 
jp.setBorder(new TitledBorder("Directions")); 
jp.add(up); 
jp.add(down); 
jp.add(left); 
jp.add(right); 
contentPane.add(jp); pack(); 
setVisible(true); 
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } 
public static void main(String[] args) 
{ 
new ButtonDemo("Hello"); 
} 
}