居然传递的值为Null

zhao9302 2008-07-10 12:31:39

这是一个计算器的程序用swing写的框架



MainFrame.java

(代码太长 截取关键的)

...

public MainFrame(Control ct)

	{

		this.ct = ct;

		getFrame();

	}

...



//其中一个按钮的代码，其他按钮代码类似

private JButton getBackSpaceButton()

	{

		if (BackSpaceButton == null)

		{

			BackSpaceButton = new JButton();

			BackSpaceButton.setBounds(new Rectangle(22, 102, 112, 43));

			BackSpaceButton.setText("BackSpace");

			BackSpaceButton.addActionListener(new ActionListener()

			{



				public void actionPerformed(ActionEvent e)

				{

					// TODO Auto-generated method stub

//					System.out.println(ct.s.empty());

					if(!ct.s.empty())

						System.out.println(ct.s.pop());	

				}

				

			});

		}

		return BackSpaceButton;

	}





Control.java

//这个类用来控制整个计算器，其中有一个栈

import java.util.Stack;



public class Control

{



	public Stack<Object> s = null;

	

	public static void main(String ag[])

	{

		Control ct = new Control();

		ct.programStart();

	}

	

	public void programStart()

	{		

		s = new Stack<Object>();

		new MainFrame(this);

		s.empty();

//这里 如果将new MainFrame（this）给不要的话 s.empty()不报NullPOINT错

//否则报错NULLPOINT;

//而且按BackSpace按钮也报错NULLPOINT

	}

}

...全文

200 18 打赏收藏转发到动态举报

写回复

用AI写文章

18 条回复

切换为时间正序

请发表友善的回复…

发表回复

zhao9302 2008-07-11

打赏
举报

我知道了，我在后面有个地方没写 addActionListener 所以导致执行了那句话。。。还是谢谢哈

zhao9302 2008-07-10

打赏
举报

没有修改哦。。new MainFrame(this);就是为了传进去
这是getFrame（）
private Frame getFrame()
{
if (Frame == null)
{
ShowLabel = new Label();
ShowLabel.setBounds(new Rectangle(29, 47, 354, 44));
ShowLabel.setText("");
ShowLabel.setAlignment(Label.RIGHT);

Frame = new Frame();
Frame.setLayout(null);
Frame.setSize(new Dimension(406, 409));
Frame.setTitle("计算器");
Frame.add(getBackSpaceButton(), null);
Frame.add(getMCButton(), null);
Frame.add(getMRButton(), null);
Frame.add(getMSButton(), null);
Frame.add(getMPlusButton(), null);
Frame.add(getOneButton(), null);
Frame.add(getTwoButton(), null);
Frame.add(getThreeButton(), null);
Frame.add(getFourButton(), null);
Frame.add(getFiveButton(), null);
Frame.add(getSixButton(), null);
Frame.add(getSevenButton(), null);
Frame.add(getEightButton(), null);
Frame.add(getNineButton(), null);
Frame.add(getZeroButton(), null);
Frame.add(getSignButton(), null);
Frame.add(getDotButton(), null);
Frame.add(getPlusButton(), null);
Frame.add(getMinusButton(), null);
Frame.add(getMultiplyButton(), null);
Frame.add(getDivideButton(), null);
Frame.add(getSqrtButton(), null);
Frame.add(getPercentButton(), null);
Frame.add(getReciproalButton(), null);
Frame.add(getEqualButton(), null);
Frame.add(getCEButton(), null);
Frame.add(getCButton(), null);
// Frame.add(getShowTextField(), null);
Frame.add(ShowLabel, null);

Frame.setVisible(true);
Frame.setResizable(false);
Frame.setLocation(450, 150);
Frame.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}

});

}
return Frame;
}

ZangXT 2008-07-10

打赏
举报

new MainFrame(this);
this把当前的Control作为参数传了进去。我怀疑你getFrame里面对Control的成员s做了修改导致的问题。

叶涛网站推广优化 2008-07-10

打赏
举报

getFrame（）
private Frame getFrame()
{
if (Frame == null)
{
ShowLabel = new Label();
ShowLabel.setBounds(new Rectangle(29, 47, 354, 44));
ShowLabel.setText("");
ShowLabel.setAlignment(Label.RIGHT);

ph215405357 2008-07-10

打赏
举报

ding

zhao9302 2008-07-10

打赏
举报

。？？~

zhao9302 2008-07-10

打赏
举报

恩恩是啊。。我郁闷但是getFrame（）的程序我也贴出来了没发现有什么问题啊

ZangXT 2008-07-10

打赏
举报

public MainFrame(Control ct)
{
System.out.println(ct.s);
this.ct = ct;
System.out.println(ct.s);
getFrame();
System.out.println(ct.s);
}
我这样改了
输出结果是：
[]
[]
null
getFrame()之后s就为null了.

zhao9302 2008-07-10

打赏
举报

import java.util.Stack;

public class Control
{

public Stack<Object> s = null;

public static void main(String ag[])
{
Control ct = new Control();
ct.programStart();
}

public void programStart()
{
s = new Stack<Object>();
new MainFrame(this);
s.empty(); //是这句话只是作为测试的时候加上的其实这里如果我用的是 s.pop()或者s.push(1)之类的也是报错同样的错误也就是说只要我运行了new MainFrame（this）这句话就是这个样子。如果我不用这句话，我后面的是可以正常不报错的
}}

ZangXT 2008-07-10

打赏
举报

at Control.programStart(Control.java:18)
看看这是哪句

zhao9302 2008-07-10

打赏
举报

public MainFrame(Control ct)
{
System.out.println(ct.s);
this.ct = ct;
System.out.println(ct.s);
getFrame();
System.out.println(ct.s);
}
我这样改了
输出结果是：
[]
[]
null
Exception in thread "main" java.lang.NullPointerException
at Control.programStart(Control.java:18)
at Control.main(Control.java:11)

如果我再按一个按钮BackSpace的话
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at MainFrame$2.actionPerformed(MainFrame.java:147)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6038)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
at java.awt.Component.processEvent(Component.java:5803)
at java.awt.Container.processEvent(Container.java:2058)
at java.awt.Component.dispatchEventImpl(Component.java:4410)
at java.awt.Container.dispatchEventImpl(Container.java:2116)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
at java.awt.Container.dispatchEventImpl(Container.java:2102)
at java.awt.Window.dispatchEventImpl(Window.java:2429)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

ZangXT 2008-07-10