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
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.
*/
}
}
}
# 1 楼答案
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:
# 2 楼答案
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强>
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:
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!;)
# 3 楼答案
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:
# 4 楼答案
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