java如何让我的程序从一个输入字段计算两个方程式？

Question

我需要从用户那里计算两个函数，我想知道如何使用相同的输入字段在对话框中显示这两个答案。我已经上了商科sci课程的第四个星期了，我觉得自己有点麻烦了。我们被要求使用JOptionPane做这个程序，但我想做得更多，并创建了自己的程序

到目前为止，我所做的是，程序在JGrasp和Eclipse中正确编译，但在运行应用程序时显示了这一点

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
    at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
    at java.lang.Double.parseDouble(Double.java:538)
    at Nicolas_Carabajal_Assignment3$CalcButtonListener.actionPerformed(Nicolas_Carabajal_Assignment3.java:57)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6525)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3322)
    at java.awt.Component.processEvent(Component.java:6290)
    at java.awt.Container.processEvent(Container.java:2234)
    at java.awt.Component.dispatchEventImpl(Component.java:4881)
    at java.awt.Container.dispatchEventImpl(Container.java:2292)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
    at java.awt.Container.dispatchEventImpl(Container.java:2278)
    at java.awt.Window.dispatchEventImpl(Window.java:2739)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:751)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:702)
    at java.awt.EventQueue$3.run(EventQueue.java:696)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:724)
    at java.awt.EventQueue$4.run(EventQueue.java:722)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:721)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

守则：

 /**
 * 
 *@author ngc5043
 *@version 1.0 
 */

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

public class Nicolas_Carabajal_Assignment3 extends JFrame
{
private JPanel panel;
private JLabel messageLabel;
private JTextField ExTextField;
private JButton calcButton;
private final int WINDOW_WIDTH = 310;
private final int WINDOW_HEIGHT = 100;


 public static void main(String[] args)
  {
      Nicolas_Carabajal_Assignment3 main = new Nicolas_Carabajal_Assignment3();
      main.buildPanel();
  }
  public Nicolas_Carabajal_Assignment3()
  {
    setTitle("Expressions Window");
    setSize(WINDOW_WIDTH,WINDOW_HEIGHT);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    buildPanel();
    add(panel);
    setVisible(true);
  }

   private void buildPanel()
   {
       messageLabel = new JLabel("Please Enter a Number");
       ExTextField = new JTextField(10);
       calcButton = new JButton("Calculate");
       calcButton.addActionListener(new CalcButtonListener());
       panel = new JPanel();
       panel.add(messageLabel);
       panel.add(ExTextField);
       panel.add(calcButton);
   }

   private class CalcButtonListener implements ActionListener
  {
      public void actionPerformed(ActionEvent e)
       {
           String input;
           int num_ent = 0;
           double answerOne;


           input = ExTextField.getText();
           answerOne = Double.parseDouble(input);
           answerOne = num_ent * num_ent;
           JOptionPane.showMessageDialog(null, "Your Answer Is" + answerOne);

        /**
        * here i would like to add another function. input*(n+1.0)/2.0
        *Getting the same number from the user and calculating this aswell. 
        */ 



       }

   }


}

Answer 1

您调用了buildpanel方法两次，这就是字符串为空的原因，现在它将字符串转换为双精度并打印出来：

     /**
 * 
 *@author ngc5043
 *@version 1.0 
 */

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

public class Nicolas_Carabajal_Assignment3 extends JFrame
{
    private JPanel panel;
    private JLabel messageLabel;
    private JTextField ExTextField;
    private JButton calcButton;
    private final int WINDOW_WIDTH = 310;
    private final int WINDOW_HEIGHT = 100;


 public static void main(String[] args)
  {
      Nicolas_Carabajal_Assignment3 main = new Nicolas_Carabajal_Assignment3();

  }
  public Nicolas_Carabajal_Assignment3()
  {
      buildPanel();
    setTitle("Expressions Window");
    setSize(WINDOW_WIDTH,WINDOW_HEIGHT);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    add(panel);
    setVisible(true);
  }

   private void buildPanel()
   {
       messageLabel = new JLabel("Please Enter a Number");
       ExTextField = new JTextField(10);
       calcButton = new JButton("Calculate");

       panel = new JPanel();
       panel.add(messageLabel);
       panel.add(ExTextField);
       panel.add(calcButton);
       calcButton.addActionListener(new CalcButtonListener());
   }

   private class CalcButtonListener implements ActionListener
  {
      public void actionPerformed(ActionEvent e)
       {
           String input;
           int num_ent = 0;


           input = ExTextField.getText();

           System.out.println(input);

           double answerOne = Double.parseDouble(input);
           System.out.println(answerOne);
           answerOne = num_ent * num_ent;
           JOptionPane.showMessageDialog(null, "Your Answer Is" + answerOne);

        /**
        * here i would like to add another function. input*(n+1.0)/2.0
        *Getting the same number from the user and calculating this aswell. 
        */ 



       }

   }


}

Answer 2

这一行： 答案一=双。解析双精度（输入）； 正在引发异常，因为输入为空

如果您在此处查看： http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html 搜索parseDouble，您将在文档中找到以下内容： NumberFormatException-如果字符串不包含可解析双精度

如果您检查stacktrace，您将看到： 在爪哇。朗，双人。parseDouble（Double.java:538）

这就是你知道问题出在哪里的原因

我的建议是使用NetBeans或Eclipse之类的工具来帮助您在代码引发异常时定位行号，并逐行调试它，以查看变量的内容发生变化

在管线周围使用Try/Catch：

input = ExTextField.getText();

或者在输入中进行检查，如isNumber（输入）

这样，您将避免这种意外错误

我希望这有帮助！；）

Answer 3

异常堆栈显示一个java。NumberFormatException：出现从java继承的空字符串。朗，双人。parseDouble方法。 Java文档（public static double parseDouble(String s) throws NumberFormatException）写到，如果字符串不包含可解析的双精度，则会引发NumberFormatException

因此，问题是调用了按钮的操作处理程序，但textbox不包含任何可解析的值。要解决这个问题，您必须处理抛出的异常。一种可能的解决方案如下：

public void actionPerformed(ActionEvent e)
{
    String input;
    int num_ent = 0;
    double answerOne;

    input = ExTextField.getText();
    try
    {
        answerOne = Double.parseDouble(input);
    }
    catch (NumberFormatException ex)
    { 
       JOptionPane.showMessageDialog(null, "Bad or empty input field");
       return;
    }
    //...
}

Answer 4

考虑下面的代码。它做两件事：如果输入不是数字，则捕获NumberFormatException，并添加一个answerTwo变量，该变量将被计算并连接到应答显示字符串

private class CalcButtonListener implements ActionListener
{
  public void actionPerformed(ActionEvent e)
  {
    String input = ExTextField.getText();
    try  {
      double num_ent = Double.parseDouble(input);
      double answerOne = num_ent * num_ent;
      double answerTwo = num_ent * (num_ent + 1.0) / 2.0;
      JOptionPane.showMessageDialog(null, "Your Answers are " + answerOne + " and " + answerTwo);
    } catch (NumberFormatException e) {
      JOptionPane.showMessageDialog(null, "Invalid input " + input);
    }
  }
}