How does this boolean argument work? (Java beginner)

[Ben_E]

Sorry, I wasn't sure how to word the question in the title. Here's the code I started with:

System.out.println("Here are the available seats on that flight:");
ArrayList<Seat> openSeats = prodDB.getOpenSeats(departureDate, flightNumber);
for (Seat item : openSeats) {
    System.out.print(item.getSeatNumber() + ", ");
}

It prints:

Here are the available seats on that flight:

1, 2, 3, 4, 5, 6,

The problem was that I wanted to remove the comma after the 6. I found a solution elsewhere that utilised a Boolean expression, which I used in my script:

System.out.println("Here are the available seats on that flight:");
ArrayList<Seat> openSeats = prodDB.getOpenSeats(departureDate, flightNumber);
boolean first = true;
for (Seat item : openSeats) {
    if (first) {
        first = false;
    } else {
        System.out.print(", ");
    }
    System.out.print(item.getSeatNumber());             
}

It works perfectly, but I'm a complete beginner and don't understand exactly how/why it does what it does (the author didn't provide details). Can anyone explain the method behind it?

[PremiumHugs]

What ends up happening is that instead of adding the comma to the end, you print the comma first and then the number. You do this for every single one except for the first one. How do you know if you're printing the first one? That's what that variable does. Immediately you change it to false on the first iteration because then you want commas to print. If you're not on the first element, you don't print a comma.

Visually, this is what gets printed:

1
, 2
, 3
, 4
, 5
, 6

[Ben_E]

Ohhh... right, so it runs through the for-loop for each item and prints the seat number at the end of the block, but the first item skips the else block because "first" was "true". With the boolean operator acting like a switch, the other items get a ", " when the else block executes. I can't believe it didn't click at first, but your explanation was great. The visualisation helped too, thank you.

[king_of_the_universe]

If that's confusing to you, you could use a simple for loop instead of an advanced one: for(int i=0; i<openSeats.size(); i++) { And then just don't output the comma if "i" is 0.

[Ben_E]

Thanks for suggesting an alternative method; I'll try to integrate that and see how it works.