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Class Calculator.CalculatorState

java.lang.Object
   |
   +----Calculator.CalculatorState

public class CalculatorState

extends Object

• Am I (in the middle of) reading a number?
• Have I seen the decimal point yet?
• Have I seen an operation that I'll do (just as soon as I get its second operand)?
• What was its first operand, anyway?

See Also:

Calculator

CalculatorState()

doneReadingNumber()

Should be called whenever a non-digit (non-dot) is seen.

getPendingOperation()

Accessor ("getter") method for pending operation.

getPreviousOperand()

Accessor ("getter") method for previous operand.

justSawDot()

Should be called when a dot is seen.

noDotYet()

A test to see if we've seen a decimal place in the number we're currently reading.

notReadingNumber()

A test to see if state is in middle of reading number.

reset()

Restores the CalculatorState to its pristine start state.

resetPendingOperation()

Should be called when no operations are pending, e.g., after = or reset.

setPendingOperation(OpButtonObj)

Should be called whenever an operation is seen.

setPreviousOperand(double)

Mutator ("setter") method for previous operand.

startReadingNumber()

Should be called whenever a first digit is seen.

 public CalculatorState()

 public void reset()

Restores the CalculatorState to its pristine start state.

• No pending operation.
• No previously seen operand (use 0).
• Haven't seen first digit.
• Haven't seen dot.

Aesthetic note: this should really be called by the constructor instead of initializing each field separately. That way, "default" is defined in a single place.

 public void startReadingNumber()

Should be called whenever a first digit is seen. Updates state to start composing numbers and a (single) decimal point.

 public void doneReadingNumber()

Should be called whenever a non-digit (non-dot) is seen. Updates state to reflect that number is done, i.e., new digit starts new number.

 public boolean notReadingNumber()

A test to see if state is in middle of reading number.

Returns:

s false if called when in middle of reading number, true otherwise.

 public boolean noDotYet()

A test to see if we've seen a decimal place in the number we're currently reading.

Returns:

s true if called after a decimal place has been seen in this number, false if number is integral.

 public void justSawDot()

Should be called when a dot is seen. Modifies state to indicate that a decimal place has already been seen in this number.

 public void setPendingOperation(OpButtonObj currOp)

Should be called whenever an operation is seen. Records that operation for future use (after second operand is seen).

Parameters:

currOp - the operation button seen.

 public void resetPendingOperation()

Should be called when no operations are pending, e.g., after = or reset. Makes pendingOperation NOOP.

This should be the sole place that this default is set, so really reset() should call this method. That way, if we ever want to change the Calculator's default state, this is the one place we'd have to make the change.

 public OpButtonObj getPendingOperation()

Accessor ("getter") method for pending operation.

Returns:

s the currently pending operation (waiting to be done).

 public void setPreviousOperand(double num)

Mutator ("setter") method for previous operand. Remembers this operand until after the operation, second operand are available and the result can be computed.

Parameters:

num - the operand to remember.

 public double getPreviousOperand()

Accessor ("getter") method for previous operand.

Returns:

s the remembered left-hand operand (waiting to be operated upon).

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