计算器GUI ActionPerformed方法，并包装另一个类

Question

我试图将一个计算器GUI包装在我构建的类上，以不同的方式计算值（不是正常的方式，反向波兰表示法）。

我只是想知道两件事：

1）如何编写actionPerformed方法，以便在单击按钮或操作时，它会显示在显示中

2）如何使用GUI和计算方法（比如如何使用GUI，当你按下GUI上的所有数字或运算符时，它会在我的计算类中注册）。基本上如何将GUI包装在它上面？

**编辑，我编辑了我的代码，但是当它编译时它给了我一个空指针异常，怎么回事？

到目前为止我的GUI类：

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;

public class GUI extends JFrame implements ActionListener
{
JPanel buttonPanel, topPanel, operationPanel;
JTextField display;

doMath math = new doMath();

JButton Num1;
JButton Num2;
JButton Num3;
JButton Num4;
JButton Num5;
JButton Num6;
JButton Num7;
JButton Num8;
JButton Num9;
JButton Num0;

JButton Add;
JButton Sub;
JButton Mult;
JButton Div;
JButton Eq;
JButton Clr;
public GUI()
{
    super("Calculator");
    setSize(400,400);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel mainPanel = new JPanel();
    mainPanel.setLayout(new GridLayout (2,1));

    buttonPanel = new JPanel();        
    buttonPanel.setLayout(new GridLayout(4, 4));
    buttonPanel.add(Num1 = new JButton("1"));
    buttonPanel.add(Num2 = new JButton("2"));
    buttonPanel.add(Num3 = new JButton("3"));
    buttonPanel.add(Num4 = new JButton("4"));
    buttonPanel.add(Num5 = new JButton("5"));
    buttonPanel.add(Num6 = new JButton("6"));
    buttonPanel.add(Num7 = new JButton("7"));
    buttonPanel.add(Num8 = new JButton("8"));
    buttonPanel.add(Num9 = new JButton("9"));
    buttonPanel.add(Num0 = new JButton("0"));        
    buttonPanel.add(Clr = new JButton("C"));
    buttonPanel.add(Eq = new JButton("="));
    buttonPanel.add(Add = new JButton("+"));
    buttonPanel.add(Sub = new JButton("-"));
    buttonPanel.add(Mult = new JButton("*"));
    buttonPanel.add(Div = new JButton("/"));


    Num1.addActionListener(this);
    Num2.addActionListener(this);
    Num3.addActionListener(this);
    Num4.addActionListener(this);
    Num5.addActionListener(this);
    Num6.addActionListener(this);
    Num7.addActionListener(this);
    Num8.addActionListener(this);
    Num9.addActionListener(this);
    Num0.addActionListener(this);
    Clr.addActionListener(this);
    Eq.addActionListener(this);
    Add.addActionListener(this);
    Sub.addActionListener(this);
    Mult.addActionListener(this);
    Div.addActionListener(this);

    topPanel = new JPanel();         
    topPanel.setLayout(new FlowLayout());
    topPanel.add(new JTextField(20));
   //jtfResult.setHorizontalAlignment(JTextField.RIGHT);
   // jtfResult.setEditable(false);  

    add(mainPanel);

    mainPanel.add(topPanel, BorderLayout.NORTH);
    mainPanel.add(buttonPanel, BorderLayout.SOUTH);

    setVisible(true);

}

public void actionPerformed(ActionEvent e) 
{
     if(e.getSource() == Num1)
    {
        s += "1";
        display.setText(s);
    }
    if(e.getSource() == Num2)
    {
        s += "2";
        display.setText(s);
    }
    if(e.getSource() == Num3)
    {
        s += "3";
        display.setText(s);
    }
    if(e.getSource() == Num4)
    {
        s += "4";
        display.setText(s);
    }
    if(e.getSource() == Num5)
    {
        s += "5";
        display.setText(s);
    }
    if(e.getSource() == Num6)
    {
        s += "6";
        display.setText(s);
    }
    if(e.getSource() == Num7)
    {
        s += "7";
        display.setText(s);
    }
    if(e.getSource() == Num8)
    {
        s += "8";
        display.setText(s);
    }
    if(e.getSource() == Num9)
    {
        s += "9";
        display.setText(s);
    }
    if(e.getSource() == Num0)
    {
        s += "0";
        display.setText(s);
    }
    if(e.getSource() == Add)
    {
        s += "+";
        display.setText(s);
    }
    if(e.getSource() == Sub)
    {
        s += "-";
        display.setText(s);
    }
    if(e.getSource() == Mult)
    {
        s += "*";
        display.setText(s);
    }
    if(e.getSource() == Div)
    {
        s += "/";
        display.setText(s);
    }
    if(e.getSource() == Eq)
    {
        String result = "" + math.doMath1(s);
        display.setText(result);
    }

}
}

我的计算类（按预期工作，只需知道如何将GUI包装在其上）：

public class doMath
{
Stack stack = new Stack();

String next = "";

public doMath()
{

}

public int doMath1(String expr)
{
    while( expr.length()  >0) //for(int i = 0; i < expr.length(); i++)
{              
    if(expr.length() == 0)
        return 0;
    if(expr.indexOf(" ")>0)
    {
        next = expr.substring(0,expr.indexOf(" "));

        if(next.equals("+"))
            stack.push(stack.pop() + stack.pop());
        else if(next.equals("-"))
        {
            int x = stack.pop();
            stack.push(stack.pop()- x);
        }
        else if(next.equals("*"))
            stack.push(stack.pop() * stack.pop());
        else if(next.equals("/"))
        {
            int x = stack.pop();
            stack.push(stack.pop()/ stack.pop());
        }
        else 
        stack.push(new Integer(Integer.parseInt(next)));         
         expr = expr.substring(expr.indexOf(" ")+1);
    }        
}

    return stack.pop();
}    
}

错误：

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at GUI.actionPerformed(GUI.java:126)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1849)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2169)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
at     javax.swing.plaf.basic.BasicButtonListener.
    mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:5517)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3129)
at java.awt.Component.processEvent(Component.java:5282)
at java.awt.Container.processEvent(Container.java:1966)
at java.awt.Component.dispatchEventImpl(Component.java:3984)
at java.awt.Container.dispatchEventImpl(Container.java:2024)
at java.awt.Component.dispatchEvent(Component.java:3819)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4212)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3892)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3822)
at java.awt.Container.dispatchEventImpl(Container.java:2010)
at java.awt.Window.dispatchEventImpl(Window.java:1791)
at java.awt.Component.dispatchEvent(Component.java:3819)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
at         java.awt.EventDispatchThread.pumpOneEventForHierarchy
    (EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy
    (EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)

Answer 1

从您的代码中，您似乎有一个可行的模型。

基本上您需要在每个按钮上附加ActionListener。在您的情况下，我将使用同一个侦听器的单个实例...

ActionListener calculatorActionHandler = new CalculatorActionHandler();
Num1.addActionListener(calculatorActionHandler);

在这个处理程序中，我将获取按钮的文本并将它们连接在一起

public class CalculatorActionHandler implements ActionListener {
    private StringBuilder expression = new StringBuilder(32);
    private Gui gui;

    public CalculatorActionHandler(Gui gui) {
        this.gui = gui;
    }

    public void actionPerformed(ActionEvent e) {
        JButton source = (JButton)e.getSource();
        String text = source.getText();
        if (text.equals("=")) {
            doMath math = new doMath();
            int result = math.doMath1(expression.toString());
            expession = new StringBuilder(32);
            // Update the UI
        } else {
            expession.append(text);
            // Update this value to the screen, maybe using a JLabel
        }
    }
}

Answer 2

通过实施ActionListener，您已经有了一个良好的开端。

您需要添加

addActionListener(this)

到您的每个JButton。

然后对于每个按钮，您需要一个if语句，或者在这种情况下可能会更好，但它应该如下所示：

String text = "";

....

if(e.getSource() == Num1)
{
    text += "1"
    display.setText(text);
}

/*continue this pattern for the other
  buttons, adding the character to the 
  text string */

对于你的等号按钮，在输入的表达式上调用doMath方法并将结果写入显示。

上述代码中可能存在错误，您应该查阅我在上述评论中发布的链接。