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Class Calculator.OpButtonObj

java.lang.Object
   |
   +----Calculator.ButtonObj
           |
           +----Calculator.OpButtonObj

public class OpButtonObj

extends ButtonObj

See Also:

Calculator

NO_OP_BUTTON_OBJ

The one and only NOOP button.

OpButtonObj(int, ButtonObj, CalcTextGUI, CalculatorState)

How to make one: Make a ButtonObj (i.e., my superclass) and also remember which operation I am (Calculator.OP_ADD, etc.), and always remember that equals button!

doOperation(double, double)

This method is called when it is actually time to calculate the result of this operation (i.e., by = button).

handleButton()

This method is called by the ButtonHandler whenever the decimal point button is pressed.

 public static final OpButtonObj NO_OP_BUTTON_OBJ

The one and only NOOP button. It exists mostly to not be one of the other objects, so the most important thing about it is that it isn't one of the others. However, it isn't null, either, in case its handleButton ever gets called. (If its handleButton does get called, it doesn't do anything. Kind-of like a NOOP, no?)

Initialized here, can't change. Note: static, so it belongs to the class: OpButtonObj.NO_OP_BUTTON_OBJ. It IS an instance of the class, though.

 public OpButtonObj(int op,
                    ButtonObj equalButton,
                    CalcTextGUI gui,
                    CalculatorState stateObj)

How to make one: Make a ButtonObj (i.e., my superclass) and also remember which operation I am (Calculator.OP_ADD, etc.), and always remember that equals button!

Parameters:

op - Which buttonID for whichever operation I am.

equalButton - The equal ButtonObj for this calculator.

gui - The CalcTextGUI to keep track of.

stateObj - The CalculatorState to keep track of.

 public void handleButton()

This method is called by the ButtonHandler whenever the decimal point button is pressed.

How to handle (my button) being pressed?

• We're not reading a number any more. Notify state.
• If there's already a pending operation, resolve it by pretending that the = button was pressed.
• Remember the number that will (eventually) be the left-hand operand to this operation.

Overrides:

handleButton in class ButtonObj

 public double doOperation(double leftOperand,
                           double rightOperand)

This method is called when it is actually time to calculate the result of this operation (i.e., by = button). It does the appropriate numeric calculation on its operands and returns the result, i.e., leftOperand + - * / rightOperand as appropriate.

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