You could do something simple like this:
private boolean additionPerformed;
public Calculation() {
this.additionPerformed = false;
mOperand = 0;
mWaitingOperand = 0;
mWaitingOperator = "";
mCalculatorMemory = 0;
}
protected void performWaitingOperation() {
if (mWaitingOperator.equals(ADD) && additionPerformed == false) {
mOperand = mWaitingOperand + mOperand;
additionPerformed = true;
} else if (mWaitingOperator.equals(SUBTRACT)) {
mOperand = mWaitingOperand - mOperand;
} else if (mWaitingOperator.equals(MULTIPLY)) {
mOperand = mWaitingOperand * mOperand;
} else if (mWaitingOperator.equals(DIVIDE)) {
if (mOperand != 0) {
mOperand = mWaitingOperand / mOperand;
}
}
}
Of course, you would have to work your logic around to not affect the flow of the calculator.