菜鸟求助！做了个简易计算器，但是运行结果异常！实在想不通什么问题造成的！

[wainiyitao2010]

如图，已经做好的程序，Ecilpse里也没有报错！但是点了按钮“+”就出现问题了！


异常问题：
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
at sun.misc.FloatingDecimal.parseDouble(Unknown Source)
at java.lang.Double.parseDouble(Unknown Source)
at com.Frame.MyFrame9.actionPerformed(Example9Test.java:65)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

这里显示了是65行的问题，我看了我的65行是这样的：z = Double.parseDouble(s3);
完整的显示是这样：
public void actionPerformed(ActionEvent e) {
String s1, s2, s3;
s1 = fieldName1.getText();
s2 = fieldName2.getText();
s3 = fieldResult.getText();
double x, y, z;
x = Double.parseDouble(s1);// 调用Double工具类的方法
y = Double.parseDouble(s2);
z = Double.parseDouble(s3); //出错的这一句？？？

if (e.getSource() == sum) {
z = x + y;
s3 = String.valueOf(z); // 转回String字符串
fieldResult.setText(s3);// 在结果里显示转的字符串
}

我觉得Z值没有什么问题，把获取到的结果存到Z，然后在JTextField文本框里用字符串显示出来，这逻辑没有啥问题，就是想不通为什么会报异常！求大神拯救！

[李德胜1995]

java.lang.NumberFormatException: empty String报错很明显了。。。 z = Double.parseDouble(s3); //出错的这一句？？？s3是空字符串“”

[wainiyitao2010]

引用 1 楼 pany1209 的回复:

java.lang.NumberFormatException: empty String报错很明显了。。。 z = Double.parseDouble(s3); //出错的这一句？？？s3是空字符串“”

但是我到了后面用了String.valueOf将数字转成字符串，然后赋值到s3里了阿，s3就应该不是空字符串了吧？

[李德胜1995]

引用 2 楼 wainiyitao2010 的回复:

[quote=引用 1 楼 pany1209 的回复:] java.lang.NumberFormatException: empty String报错很明显了。。。 z = Double.parseDouble(s3); //出错的这一句？？？s3是空字符串“”

但是我到了后面用了String.valueOf将数字转成字符串，然后赋值到s3里了阿，s3就应该不是空字符串了吧？[/quote] z = Double.parseDouble(s3); //出错的这一句？？？这一句删掉。。。

[wainiyitao2010]

引用 1 楼 pany1209 的回复:

java.lang.NumberFormatException: empty String报错很明显了。。。 z = Double.parseDouble(s3); //出错的这一句？？？s3是空字符串“”

好吧！原来是这样子！s3是不用再赋值给z，此刻是空字符串呀！然后刚刚我把这句话注释掉就没有问题了！

[wainiyitao2010]

引用 3 楼 pany1209 的回复:

[quote=引用 2 楼 wainiyitao2010 的回复:] [quote=引用 1 楼 pany1209 的回复:] java.lang.NumberFormatException: empty String报错很明显了。。。 z = Double.parseDouble(s3); //出错的这一句？？？s3是空字符串“”

但是我到了后面用了String.valueOf将数字转成字符串，然后赋值到s3里了阿，s3就应该不是空字符串了吧？[/quote] z = Double.parseDouble(s3); //出错的这一句？？？这一句删掉。。。[/quote] 嗯嗯！对！我也刚刚明白这么回事！谢谢啦~