Java 如何让我的程序从一个输入字段计算两个方程式?
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Java 如何让我的程序从一个输入字段计算两个方程式?,java,eclipse,swing,events,equation-solving,Java,Eclipse,Swing,Events,Equation Solving,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 Strin
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.
*/
}
}
}
这一行:
answerOne=Double.parseDouble(输入);
正在引发异常,因为输入为空
如果您在此处查看:
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:
位于java.lang.Double.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();
input=extfield.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!;) 考虑以下代码。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);
}
}
}
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.
*/
}
}
}
异常堆栈显示从java.lang.Double.parseDouble方法继承的java.lang.NumberFormatException:空字符串出现。 Java文档()写到,如果字符串不包含可解析的双精度,则会抛出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;
}
//...
}
使用JFormatterTextField(带数字实例)或JSpinner,请参阅Oracle教程中的工作代码示例谢谢您的回复,但我希望用户输入一个数字并用两个不同的公式计算。计算后,数字本身和数字*(数字+1.0)/2.0将显示在一个框中。使用此JOptionPane.showMessageDialog(null,“您的答案是”+Double.parseDouble(ExTextField.getText());但是如果你把你知道的(非数字字符串)放进去,你会遇到麻烦…这是正确的答案。
actionPerformed
方法中引用的ExtTextField
不是用户在屏幕上看到的字段,因为它是在main()
方法对buildPanel()的调用中重新创建的。接得好。@DavidMoles谢谢。确切地说,这是一个棘手的问题,花了20分钟才发现该方法被调用了两次:PThank you that that。我以为主播在它被调用时创建了它。我把这里的很多事情弄糊涂了,但慢慢地,它们都被弄清楚了。@ngcarabajal没问题!挥杆很难,但对学习很有帮助。如果您认为有效,请将其标记为答案;)祝你好运!:)非常感谢您的回复。我必须将'num_ent'中的'int'改为double,这样它才能正确编译。我遇到的最大问题是定义用户输入的整数,通过这段代码,我可以更好地看到它。不客气:)我更正了我的答案,以反映同样的情况。如果我的回答能帮你解决问题,请