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Java Java Objects Harnessing the Power of Objects Abstraction at Play

Jack McClelland
Jack McClelland
1,356 Points
Posted by Jack McClelland
Jack McClelland
1,356 Points

!isEmpty() was used to determine if dispenser was full - not being empty is not the same thing as being full though?

This logic doesn't make sense to me: "if the container isn't empty, then print out 'dispenser is full'" Because the dispenser could have 3 pez in it for example, which is not empty but also not full.

Also why print this out right after filling the dispenser, when it's clear that the dispenser is full?

3 Answers

Sean M
Sean M
7,344 Points
Sean M
Sean M
7,344 Points

if you're referring to this code below:

  public boolean dispense() {
        boolean wasDispensed = false;
        if (!isEmpty()) {
            pezCount--;
            wasDispensed = true;
        }
        return wasDispensed;
    }

The !isEmpty is checking if it's not empty, not if it's full. If it's not empty, it will decrement the pezCount.

Anastasios Poursaitedes
Anastasios Poursaitedes
10,491 Points
Anastasios Poursaitedes
Anastasios Poursaitedes
10,491 Points

Hey Jack, before we check if the dispenser is not empty we fill the dispenser with the fill() method. I think Graig just illustrated that if we do the check again we will see that the dispenser has been filled and it's no longer empty.

Luis Marsano
Luis Marsano
21,425 Points
Luis Marsano
Luis Marsano
21,425 Points

Right, it's a domain logic error to infer from the condition alone that the dispenser is full. If we're including previous statements and the condition to justify the assertion, then the condition serves no purpose, since the assertion follows from previous statements alone. You could call it a poor example.