面板按钮测试出现的问题

2014-09-10 09:40:42 145 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

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package Tx;



import java.awt.*;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;



import javax.swing.*;



public class ButtonTestOne {

	public static void main(String [] args){

		EventQueue.invokeLater(new Runnable(){

			public void run()

			{

				ButtonFrame frame = new ButtonFrame();

				frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

				frame.setVisible(true);

			}

		});

	}

}



class ButtonFrame extends JFrame{

	public ButtonFrame(){

		setTitle("ButtonTestOne");

		setSize(width, height);



		makeButton("yellow", Color.YELLOW);

		makeButton("blue", Color.BLUE);

		makeButton("red", Color.RED);

		

		add(buttonPanel);

	}

	

	public void makeButton(String name, final Color backgroundColor){

		JButton button = new JButton(name);

		buttonPanel.add(button);

		button.addActionListener(new ActionListener() {

			public void actionPerformed(ActionEvent e){

				buttonPanel.setBackground(backgroundColor);

			}

		});

	}

	

	private JPanel buttonPanel;

	private static final int width = 300;

	private static final int height = 200;

}

以下为测试时出现的异常，该怎么解决？

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

	at Tx.ButtonFrame.makeButton(ButtonTestOne.java:36)

	at Tx.ButtonFrame.<init>(ButtonTestOne.java:27)

	at Tx.ButtonTestOne$1.run(ButtonTestOne.java:14)

	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)

	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)

	at java.awt.EventQueue.access$000(EventQueue.java:101)

	at java.awt.EventQueue$3.run(EventQueue.java:666)

	at java.awt.EventQueue$3.run(EventQueue.java:664)

	at java.security.AccessController.doPrivileged(Native Method)

	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)

	at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)

	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)

	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)

	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)

	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)

	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)

	at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)