What is the purpose or main idea behind this PezDispenser code?

Hi

Let take the Pez as an example to discuss the need for public and private designation

Let say this object (the pez) needs to be reloaded after you consumed all the goodies in the pez.

so I have (pseudo code ... and just for demo):

Class PzDespenserClass(){
  public maxNumberOfPezToReload;
  public numberOfPezInDespenser;

  //and down here I have a method 
  public reloadPz(){
      numberOfPezInDespenser = maxNumberOfPezToReload

  }
}

//here is a fake main()
public static void main(String[] args){
   PzDespenserClass myDespenser = new PzDespenserClass();
   myDespenser.maxNumberOfPezToReload = 1000;
   myDespenser.reloadPz();   <<<<<<<<<<<<<<<< I just put 1000 pez in a despenser that can takes 20 only????
}

Certainly YOU wouldn't load 1000 pez, because you know that a dispenser can only takes 20 pez. But you are not writing the class for your self ... I am the user ... and I have no clue what the max capacity of a dispenser... so I may put 500, 1000, who know ... the more the merrier. The key to understand ... a class with everything having public access .. is a disaster in making.

Noe let refactor the class.

Class PzDespenserClass(){
  private static final maxNumberOfPezToReload=20;
  private numberOfPezInDespenser;

  public void setNumberOfPezInDespenser(int pezToAdd){
     if (pezToAdd > maxNumberOfPezToReload ) {
         FatWarining();
     }
     else if(maxNumberOfPezToReload  < 1){
         StarvingWarning();
    } 
    else
         numberOfPezInDespenser = pezToAdd;
  }
  //
  private void FatWarning(){
     System.out.Println("Hey ... you are making me too fat.   Too many pez");
  }

  private void StarvingWarning(){
     System.out.Println("Comon man... some pez please.   TI am starving");
  }
}

//here is a fake main()
public static void main(String[] args){
   PzDespenserClass myDespenser= new PzDespenserClass();
   //  myDespenser.maxNumberOfPezToReload = 1000;           <<<<<<<<<<<<< and to that any more
   //myDespenser.reloadPz();   <<<<<<<<< no more direct access
   //
   // what you can do is
   myDespenser.setNumberOfPezInDespenser(1000); // <<<<<<<< you will get the message from FatWarning
   myDespenser.setNumberOfPezInDespenser(-500); // <<<<<<<< you will get the message from StarvingWarning
   myDespenser.setNumberOfPezInDespenser(10) // works, and now you / I got 10 pez to enjoy.

this is all pseudo code typed in very cumbersome text area, but I hope it conveys the concept. Class attributes must be private modifier as much as possible (if not in all cases), and access to them should be done via public setters and getters.

Hope this helps. If this answers your question, please mark question as answered.

I just finished this exercise, so I might not quite get it either, but I understood it less like "secret blueprints" and more like a warning. Like, for example your PC has some really important system files that can brick your machine if you edit or delete them, and if you were to try, Microsoft (on PC of course) will tell you "NO!"

You know that the files are there, and if you really want to, you could force your way in (administrator) and delete your system32 or something, but Microsoft makes it abundantly clear that you really shouldn't do that. Likewise, a private class warns the consumer that that bit of the class is really important and really shouldn't be touched. If the consumer wants to, they can just go in and change it (if they know how to edit the file directly, like an administrator), but they really shouldn't.

Is that right?

EDIT: Just noticed this post is 6 months old, sorry for necro.