“线程中的异常”；AWT-EventQueue-0“；简单计算器（JAVA）

我正在尝试用java做一个简单的计算器。它只需要考虑基本的四个操作。我认为逻辑是正确的，但是当我运行它时，我得到以下错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at simpleCalc$1equalsListener.actionPerformed(simpleCalc.java:118)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$400(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

有人能帮我吗？我对这个错误信息做了一些研究，但无法缩小代码中的问题范围。这是我的密码：

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class simpleCalc extends JFrame {
    /**
     * 
     */
    private boolean firstNum = true;
    private String numstr1 = " ";
    private String numstr2 = " ";
    private double num1;
    private double num2;
    private String opused;
    private double ans;
    private String finalans;
    public static void main(String[] args) {
        simpleCalc window = new simpleCalc();
    }

public simpleCalc() {

    setSize(400, 400);
    setTitle("Calculator");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    int width = 10;
    JPanel panel = new JPanel();
    JTextField textField = new JTextField(width);
    Container contentPane = getContentPane();
    contentPane.setLayout(new BorderLayout());
    panel.add(textField);
    contentPane.add(panel, BorderLayout.NORTH);

    String[] calcnumbers = { "0", "1", "2", "3", "4", "5", "6", "7", "8",
            "9" };
    JPanel numpanel = new JPanel();// number for calc start point
    numpanel.setLayout(new GridLayout(2, 2));

    for (int i = 0; i < calcnumbers.length; i++) {
        JButton calcButton = new JButton(calcnumbers[i]);
        class cbListener implements ActionListener {
            public void actionPerformed(ActionEvent event) {
                JButton thebutton = (JButton) event.getSource();
                if (firstNum) {
                    String currentText = textField.getText();
                    String newText = currentText + thebutton.getText();
                    textField.setText(newText);
                    numstr1 = numstr1 + thebutton.getText();
                } else {
                    textField.setText(" ");
                    String currentText = textField.getText();
                    String newText = currentText + thebutton.getText();
                    textField.setText(newText);
                    numstr2 = numstr2 + thebutton.getText();

                }
            }

        }

        cbListener cb = new cbListener();
        calcButton.addActionListener(cb);// end calcbuttons
        numpanel.add(calcButton);
        contentPane.add(numpanel, BorderLayout.CENTER);

    }

    String[] calcoperators = { "*", "+", "-", "/", };

    JPanel oppanel = new JPanel();
    oppanel.setLayout(new GridLayout(2, 2));
    for (int c = 0; c < calcoperators.length; c++) {
        JButton opButton = new JButton(calcoperators[c]);
        oppanel.add(opButton);
        contentPane.add(oppanel, BorderLayout.EAST);
        class opListener implements ActionListener {
            public void actionPerformed(ActionEvent event) {
                JButton theOP = (JButton) event.getSource();
                String opused = theOP.getText();
                firstNum = false;

                // String currentText = textField.getText();
                // String newText = currentText + theOP.getText();
                // textField.setText(newText);

            }
        }
        opListener ob = new opListener();
        opButton.addActionListener(ob);

    }
    JButton clear = new JButton("C");
    oppanel.add(clear);
    class clearListener implements ActionListener {
        public void actionPerformed(ActionEvent event) {
            JButton theClear = (JButton) event.getSource();
            textField.setText("");
        }
    }
    clearListener cl = new clearListener();
    clear.addActionListener(cl);

    JButton equals = new JButton("=");
    oppanel.add(equals);
    class equalsListener implements ActionListener {
        public void actionPerformed(ActionEvent event) {
            JButton theEquals = (JButton) event.getSource();
            textField.setText(" ");
            num1 = Double.parseDouble(numstr1);
            num2 = Double.parseDouble(numstr2);
            if (opused.equals("*")){
                ans = (num1 * num2 );
            }
            else if (opused.equals("/")){
                ans = (num1 / num2);
            }
            else if (opused.equals("+")){
                ans = (num1 + num2);
            }
            else if (opused.equals("-")){
                ans = (num1 - num2);
            }

            textField.setText(Double.toString(ans));
        }
    }
    equalsListener el = new equalsListener();
    equals.addActionListener(el);
    pack();
    setVisible(true);

}

导入java.awt.BorderLayout；
导入java.awt.Container；
导入java.awt.GridLayout；
导入java.awt.event.ActionEvent；
导入java.awt.event.ActionListener；
导入javax.swing.JButton；
导入javax.swing.JFrame；
导入javax.swing.JPanel；
导入javax.swing.JTextField；
公共类simpleCalc扩展了JFrame{
/**
* 
*/
私有布尔值firstNum=true；
私有字符串numstr1=“”；
私有字符串numstr2=“”；
私人双num1；
私人双num2；
私有字符串的使用；
私人双ans；
私有字符串finalans；
公共静态void main（字符串[]args）{
simpleCalc window=新的simpleCalc（）；
}
公共simpleCalc（）{
设置大小（400400）；
setTitle（“计算器”）；
setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）；
整数宽度=10；
JPanel面板=新的JPanel（）；
JTextField textField=新的JTextField（宽度）；
容器contentPane=getContentPane（）；
setLayout（新的BorderLayout（））；
panel.add（textField）；
添加（面板，BorderLayout.NORTH）；
字符串[]calcnumbers={“0”、“1”、“2”、“3”、“4”、“5”、“6”、“7”、“8”，
"9" };
JPanel numpanel=new JPanel（）；//计算起点的编号
设置布局（新的网格布局（2,2））；
对于（int i=0；i

---

}

您没有检查

是否设置为未初始设置，初始值为
null

你应该：


检查
equalListener.actionPerformed
（推荐）中的
opuser
是否为空
在类初始化时将
opuser
设置为空字符串

您还应该检查为什么此时
opuser
可能为
null
。

可能的情况是，用户输入一个数字，然后按
=
，而不按
操作符
按钮（这是一个有效的情况）。
在
simpleCalc$1equalListener.ActionExecuted（simpleCalc.java:118）
处有东西是
null
。