Java 计算器编程 NumberFormatException 的答案

【问题标题】：Java Calculator programming NumberFormatException'sJava 计算器编程 NumberFormatException 的
【发布时间】：2014-09-26 08:20:45
【问题描述】：

我正在尝试用 Java 制作计算器。到目前为止，我已经取得了很大的进步，但是当我尝试在计算器中进行计算时按下等号按钮时，没有任何反应，并且控制台中出现有关异常的错误消息。这些是我尝试进行 2+2 计算时出现的错误消息：

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "2+2"
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1222)
    at java.lang.Double.parseDouble(Double.java:510)
    at Calculator$1Listener.actionPerformed(Calculator.java:124)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
    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:6414)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
    at java.awt.Component.processEvent(Component.java:6179)
    at java.awt.Container.processEvent(Container.java:2084)
    at java.awt.Component.dispatchEventImpl(Component.java:4776)
    at java.awt.Container.dispatchEventImpl(Container.java:2142)
    at java.awt.Component.dispatchEvent(Component.java:4604)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4618)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4279)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4209)
    at java.awt.Container.dispatchEventImpl(Container.java:2128)
    at java.awt.Window.dispatchEventImpl(Window.java:2492)
    at java.awt.Component.dispatchEvent(Component.java:4604)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:717)
    at java.awt.EventQueue.access$400(EventQueue.java:82)
    at java.awt.EventQueue$2.run(EventQueue.java:676)
    at java.awt.EventQueue$2.run(EventQueue.java:674)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:690)
    at java.awt.EventQueue$3.run(EventQueue.java:688)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:687)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

这是我的代码：

import javax.swing.*;//import the packages needed for gui
import java.awt.*;
import java.awt.event.*;
import static java.lang.Math.*;

public class Calculator
{
    public static void main(String[] args)
    {
        JFrame window = new JFrame("Window");// makes a JFrame
        window.setSize(300, 415);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel(new FlowLayout());// makes the panel,
                                                    // textfield and buttons and
                                                    // gives the buttons
                                                    // actioncommands

        final JTextField textField = new JTextField(20);
        JButton openbracket = new JButton("(");
        openbracket.setActionCommand("(");
        JButton closebracket = new JButton(")");
        closebracket.setActionCommand(")");
        JButton clearbutton = new JButton("C");
        clearbutton.setActionCommand("C");
        JButton arcsin = new JButton("arcsin");
        arcsin.setActionCommand("arcsin");
        JButton arccos = new JButton("arccos");
        arccos.setActionCommand("arccos");
        JButton arctan = new JButton("arctan");
        arctan.setActionCommand("arctan");
        JButton sin = new JButton("sin");
        sin.setActionCommand("sin");
        JButton cos = new JButton("cos");
        cos.setActionCommand("cos");
        JButton tan = new JButton("tan");
        tan.setActionCommand("tan");
        JButton log = new JButton("log");
        log.setActionCommand("log");
        JButton seven = new JButton("7");
        seven.setActionCommand("seven");
        JButton eight = new JButton("8");
        eight.setActionCommand("eight");
        JButton nine = new JButton("9");
        nine.setActionCommand("nine");
        JButton four = new JButton("4");
        four.setActionCommand("four");
        JButton five = new JButton("5");
        five.setActionCommand("five");
        JButton six = new JButton("6");
        six.setActionCommand("six");
        JButton one = new JButton("1");
        one.setActionCommand("one");
        JButton two = new JButton("2");
        two.setActionCommand("two");
        JButton three = new JButton("3");
        three.setActionCommand("three");
        JButton zero = new JButton("0");
        zero.setActionCommand("zero");
        JButton radixpoint = new JButton(".");
        radixpoint.setActionCommand("radixpoint");
        JButton plus = new JButton("+");
        plus.setActionCommand("plus");
        JButton subtract = new JButton("-");
        subtract.setActionCommand("subtract");
        JButton multiply = new JButton("x");
        multiply.setActionCommand("multiply");
        JButton divide = new JButton("/");
        divide.setActionCommand("divide");
        JButton equal = new JButton("=");
        equal.setActionCommand("equal");

        final String values = " ";

        class Listener implements ActionListener
        {
            String out = "";

            public void actionPerformed(ActionEvent e)
            {
                String output = e.getActionCommand();
                if (output == "(")
                {
                    out = out + "(";
                    textField.setText(out);
                }
                else if (output == ")")
                {
                    out = out + ")";
                    textField.setText(out);
                }
                else if (output == "C")
                {
                    textField.setText(" ");
                    out = "";
                }
                else if (output == "arcsin")
                {
                    out = out + "asin(";
                    textField.setText(out);
                }
                else if (output == "arccos")
                {
                    out = out + "acos(";
                    textField.setText(out);
                }
                else if (output == "arctan")
                {
                    out = out + "atan(";
                    textField.setText(out);
                }
                else if (output == "log")
                {
                    out = out + "log(";
                    textField.setText(out);
                }
                else if (output == "seven")
                {
                    out = out + "7";
                    textField.setText(out);
                }
                else if (output == "eight")
                {
                    out = out + "8";
                    textField.setText(out);
                }
                else if (output == "nine")
                {
                    out = out + "9";
                    textField.setText(out);
                }
                else if (output == "four")
                {
                    out = out + "4";
                    textField.setText(out);
                }
                else if (output == "five")
                {
                    out = out + "5";
                    textField.setText(out);
                }
                else if (output == "six")
                {
                    out = out + "6";
                    textField.setText(out);
                }
                else if (output == "one")
                {
                    out = out + "1";
                    textField.setText(out);
                }
                else if (output == "two")
                {
                    out = out + "2";
                    textField.setText(out);
                }
                else if (output == "three")
                {
                    out = out + "3";
                    textField.setText(out);
                }
                else if (output == "zero")
                {
                    out = out + "0";
                    textField.setText(out);
                }
                else if (output == "radixpoint")
                {
                    out = out + ".";
                    textField.setText(out);
                }
                else if (output == "equal")
                {
                    double val = Double.parseDouble(out);
                    String str = String.valueOf(val);
                    textField.setText(str);
                }
                else if (output == "plus")
                {
                    out = out + "+";
                    textField.setText(out);
                }
                else if (output == "subtract")
                {
                    out = out + "-";
                    textField.setText(out);
                }
                else if (output == "multiply")
                {
                    out = out + "*";
                    textField.setText(out);
                }
                else if (output == "divide")
                {
                    out = out + "/";
                    textField.setText(out);
                }
            }
        }

        Listener listener = new Listener(); // makes an object of the
                                            // actionlistener
        panel.add(textField);// adding all the things
        window.add(panel);
        openbracket.addActionListener(listener);
        panel.add(openbracket);
        closebracket.addActionListener(listener);
        panel.add(closebracket);
        clearbutton.addActionListener(listener);
        panel.add(clearbutton);
        arcsin.addActionListener(listener);
        panel.add(arcsin);
        arccos.addActionListener(listener);
        panel.add(arccos);
        arctan.addActionListener(listener);
        panel.add(arctan);
        sin.addActionListener(listener);
        panel.add(sin);
        cos.addActionListener(listener);
        panel.add(cos);
        tan.addActionListener(listener);
        panel.add(tan);
        log.addActionListener(listener);
        panel.add(log);
        nine.addActionListener(listener);
        panel.add(nine);
        eight.addActionListener(listener);
        panel.add(eight);
        seven.addActionListener(listener);
        panel.add(seven);
        six.addActionListener(listener);
        panel.add(six);
        five.addActionListener(listener);
        panel.add(five);
        four.addActionListener(listener);
        panel.add(four);
        three.addActionListener(listener);
        panel.add(three);
        two.addActionListener(listener);
        panel.add(two);
        one.addActionListener(listener);
        panel.add(one);
        zero.addActionListener(listener);
        panel.add(zero);
        radixpoint.addActionListener(listener);
        panel.add(radixpoint);
        plus.addActionListener(listener);
        panel.add(plus);
        subtract.addActionListener(listener);
        panel.add(subtract);
        multiply.addActionListener(listener);
        panel.add(multiply);
        divide.addActionListener(listener);
        panel.add(divide);
        equal.addActionListener(listener);
        panel.add(equal);
        window.setVisible(true);
    }
}

我怀疑这是因为我的编码错误。谁能告诉我我的代码有什么问题以及为什么会发生这些异常？

【问题讨论】：

寻求调试帮助的问题（“为什么这段代码不起作用？”）必须包括所需的行为、特定的问题或错误以及在问题本身中重现它所需的最短代码。没有明确问题陈述的问题对其他读者没有用处。
了解如何读取 StackTrace 很重要。它说“2+2”不是一个数字。你同意吗？如果你这样做了，你应该明白你的错误。
您知道异常是java.lang.NumberFormatException 的一个实例，带有消息For input string: "2+2"。为什么不查看 NumberFormatException 的 javadoc？
请把所有这些代码提取成 2 或 3 个更小的方法！！！！
0.02 -> 你重复了很多不必要的东西。对于if/else 链中的每种情况，只需使用out="theString"; 将适当的字符串分配给out（不需要out=out+"someString";）。然后在链结束后做textField.setText(out); 除非需要，否则总是尽量避免重复。此外，如果您使用的是 Java 7+，您可以switch 字符串。

标签： java user-interface exception-handling calculator

【解决方案1】：

您不能将该 TextBox 中的所有内容解析为双精度。您只能解析仅包含数字的字符串..

试着这样做。

double num1 = Double.parseDouble(number1);

double num2 = Double.parseDouble(number2);

double val = num1 + num2;

【讨论】：

【解决方案2】：

double val = Double.parseDouble(out);

如果您先将数字解析为双倍然后执行+ 之类的数学运算，这可能会更好。解析器不知道如何将 String 2+2 解析为 double。

【讨论】：