字符串和变量连接出现JOptionPane错误

Question

我正在尝试为我所在的一个编程类制作一个计算器，它结合了用户输入，然后进行数学运算。我选择使用JOptionPane作为这个赋值的用户输入部分，一切都很顺利，直到我要求Java将字符串与之前在JOptionPane消息对话框中定义的一些变量连接起来。我正在使用DrJava。

我收到以下错误：

Error: unexpected type
  required: class
  found:    value

下面是我的代码：

(Line 1) JOptionPane.showMessageDialog(null, "Thank you! Here are your results:\n"+

(2)               "The addition of "+fnum+" and "+snum+" is "(fnum+snum)"\n"+

(3)               "The subtraction of "+fnum+" and "+snum+" is "+(5-3));

我在第二行收到错误，光标位于fnum和+ in (fnum+snum)之间

变量已经定义好了，这个过程使用System.out.println方法可以正常工作。

有什么建议吗？

Answer 1

OptionPane.showMessageDialog(null, "Thank you! Here are your results:\n"+
"The addition of "+fnum+" and "+snum+" is "+(fnum+snum)+"\n"+
"The subtraction of "+fnum+" and "+snum+" is "+(5-3));

Answer 2

这一行是的罪魁祸首，

(2) "The addition of "+fnum+" and "+snum+" is "(fnum+snum)"\n"+

不是这样，而是使用这个

(2) "The addition of "+fnum+" and "+snum+" is "+(fnum+snum)+"\n"+