title: java.lang.NumberFormatException: empty String
body: <p>The code below keeps giving a <code>java.lang.NumberFormatException: empty String</code>:</p>
  
  <pre><code>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 &amp;&amp; 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;
  }
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>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)
  </code></pre>