ADVANCED GUIS AND GRAPHICS - Java Programming: From Problem Analysis to Program Design - page 861

int [] listArray = yourChoices.getSelectedIndices();
double localTax = 0.065;
double tax;
double subtotal = 0;
double total;
Note that listArray[0] , listArray[1] ,..., listArray[listArray.length - 1]
contains the indices of the items selected from the menu list. Therefore, the
following for loop computes the total cost of the items selected from the menu:

for ( int index = 0; index < listArray.length; index++)
subTotal = subTotal + yourChoicesPrices[listArray[index]];
Next, we compute the tax and add it to subTotal to get the billing amount:

tax = localTax * subTotal;
total = subTotal + tax;
To display the bill, we append the necessary statements to the JTextArea and invoke
the repaint method to redraw the GUI components. To place another order, we
unselect the selected items. The definition of the method displayBill is:

// method to display the order and total cost
private void displayBill()
{

int [] listArray = yourChoices.getSelectedIndices();
double localTax = 0.065;
double tax;
double subtotal = 0;
double total;

//Set the text area to nonedit mode
//and start with an empty string.
bill.setEditable( false );
bill.setText("");

//Calculate the cost of the items ordered.
for ( int index = 0; index < listArray.length; index++)
subTotal = subTotal + yourChoicesPrices[listArray[index]];

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tax = localTax * subTotal;
total = subTotal + tax;

//Display costs.
bill.append(" JAVA KIOSK A LA CARTE\n\n");
bill.append("--------------- Welcome ----------------\n\n");

for ( int index = 0; index < listArray.length; index++)
{

bill.append(yourChoicesItems[listArray[index]] + "\n");

}