编写一个具有如下布局的小应用程序，要求当在上面的文本区中输入若干数时，下面的文本框同时对输入的数进行求和运算并求出平均数。即随着输入的变化，文本框不断更新求和及平均值。 实验源代码-Write an application with the following layout required, the following text box above the text area, enter a number on the number of input summation and calculated the average number of With the changes in the input text box to continue to update the sum and average values​ ​ .