下面的代码不断给出一个java.lang.NumberFormatException: empty String:

private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) {
    double AText = Double.parseDouble(angleAField.getText());
    double BText = Double.parseDouble(angleBField.getText());
    double CText = Double.parseDouble(angleCField.getText());
    double aText = Double.parseDouble(sideaField.getText());
    double bText = Double.parseDouble(sidebField.getText());
    double cText = Double.parseDouble(sidecField.getText());

    if (getMissing(angleAField.getText()) == false && getMissing(angleCField.getText()) == false) { //doesnt have angle C ,find Angle A
        double angleA = Math.round(Math.asin((Math.sin(BText) / bText) * aText));
        angleAField.setText("" + angleA);
    }
}

public boolean getMissing(String Field) {
    try {
        if (Field.equals("")) {
            return false; // has number
        }
    } catch (NumberFormatException e) {}

    return true;
}

错误:

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1011)
at java.lang.Double.parseDouble(Double.java:540)
at sowhatstrig.trigFrame.jButton4ActionPerformed(trigFrame.java:520)
at sowhatstrig.trigFrame.access$300(trigFrame.java:20)
at sowhatstrig.trigFrame$4.actionPerformed(trigFrame.java:353)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
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:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:696)
at java.awt.EventQueue$4.run(EventQueue.java:694)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

最佳答案

你应该在解析 double 之前检查你的字段:

private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) {
   double AText = ParseDouble(angleAField.getText());
   double BText = ParseDouble(angleBField.getText());
   double CText = ParseDouble(angleCField.getText());
   double aText = ParseDouble(sideaField.getText());
   double bText = ParseDouble(sidebField.getText());
   double cText = ParseDouble(sidecField.getText());

// other code here same
}

double ParseDouble(String strNumber) {
   if (strNumber != null && strNumber.length() > 0) {
       try {
          return Double.parseDouble(strNumber);
       } catch(Exception e) {
          return -1;   // or some value to mark this field is wrong. or make a function validates field first ...
       }
   }
   else return 0;
}

关于java.lang.NumberFormatException : empty String 异常，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21542079/