定义如下界面，在用户输入一个非负整数时，当点击 run按钮时把该数的阶乘在第二个文本框中显示出来，当点击restart时把两个文本框的内容都清空开始新一轮的运算-Defined as interface, the user enters a non-negative integer, when you click run button to the factorial of the number in the second text box is displayed when clicking