如何在JFrame中编写total方法，我正在使用netbeans

![***The three text boxes in this program initially disabled. To enter value in the each text box you would check mark the each check box for an item a customer was purchasing. This would enable that item's text field so you can enter the quantity. You would do this for each type of item the customer was purchasing.When you entered the quantities of each item, you would click the Total button. This would show output in the text area similar to that in the image below:![***The three text boxes in this program initi