java - Java中的GUI计算按钮编码错误

Question

好吧，首先我正在做的项目有两个包，第一个是 murach.business，其中包含发票Calculations.java 第二个是 murach.forms，其中包含 InvoiceForm.java(JFrame) 和 SwingValidator.java

我需要为计算按钮的actionPerformed 事件添加一个事件处理程序。向此事件处理程序添加代码，从表单中获取客户类型和小计，使用 InvoiceCalculations 类中的calculateDiscountPct 方法根据这些值计算折扣百分比，计算折扣金额和总计，并在表单上设置值的格式和显示值。

该表单有 5 行，例如第一个客户类型、小计、折扣百分比、折扣金额和总计，下面是计算和退出按钮。

这是堆栈跟踪:

run:
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "R"
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1222)
    at java.lang.Double.parseDouble(Double.java:510)
    at murach.forms.InvoiceForm.calculateButtonActionPerformed(InvoiceForm.java:183)
    at murach.forms.InvoiceForm.access$300(InvoiceForm.java:15)
    at murach.forms.InvoiceForm$4.actionPerformed(InvoiceForm.java:81)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
    at javax.swing.AbstractButton$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:6382)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
    at java.awt.Component.processEvent(Component.java:6147)
    at java.awt.Container.processEvent(Container.java:2083)
    at java.awt.Component.dispatchEventImpl(Component.java:4744)
    at java.awt.Container.dispatchEventImpl(Container.java:2141)
    at java.awt.Component.dispatchEvent(Component.java:4572)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210)
    at java.awt.Container.dispatchEventImpl(Container.java:2127)
    at java.awt.Window.dispatchEventImpl(Window.java:2489)
    at java.awt.Component.dispatchEvent(Component.java:4572)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:704)
    at java.awt.EventQueue.access$400(EventQueue.java:82)
    at java.awt.EventQueue$2.run(EventQueue.java:663)
    at java.awt.EventQueue$2.run(EventQueue.java:661)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
    at java.awt.EventQueue$3.run(EventQueue.java:677)
    at java.awt.EventQueue$3.run(EventQueue.java:675)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:674)
    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)
BUILD SUCCESSFUL (total time: 25 seconds)

到目前为止，当我点击代码的计算按钮时，我收到错误。这是我当前的代码，您能告诉我需要对代码进行哪些更改以及原因吗？

private void calculateButtonActionPerformed(java.awt.event.ActionEvent evt) {                                                
      // TODO add your handling code here:
   double c = Double.parseDouble(customertypeTextField.getText());
   double s = Double.parseDouble(subtotalTextField.getText());
   pct d = Percent.parsepct(discountpercentTextField.getText());
   double a = Double.parseDouble(discountamountTextField.getText());
   double total = InvoicCalculations.calculateTotal(c, s, d);
   NumberFormat currecny = NumberFormat.getCurrencyInstance();
   totalTextField.setText(currency.format(total));
}                                               

Answer 1

其中一个文本字段包含一个字母，导致 Double.parseDouble 由于无效而失败。来自 documentation :

Throws:

NullPointerException - if the string is null

NumberFormatException - if the string does not contain a parsable double.

为了防止这种情况，您可以:

• 确保当您点击计算按钮时，字段仅包含有效数据。您可以使用 InputVerifier 来完成此操作.
• 或在解析输入之前验证输入是否有效，如果无效，则显示弹出窗口或错误消息。

其他人也提到过，这里强调一下:do not use Double for representing money .