private boolean isStackEmpty() {
return stack.isEmpty();
}
private void resetStack() {
stack.reset();
}
private void push(double x) throws RrdException {
stack.push(x);
}
private double peek() throws RrdException {
return stack.peek();
}
@Override
public void execute(RpnStack values) {
values.push(values.pop().multiply(NEGATIVE_ONE));
}