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 restart when the contents of the two text boxes are empty to start a new one round operation