Question

Ok, so I have an ArrayList (arrBok), which is full of book objects (the code is in Norwegian, so pay no attention to that please). I want to make a public method which iterates through all the objects in the `ArrayList’.

When I execute the code, it just seems to run in an infinite loop, not producing any return values.

Here is the relevant (I hope, because there are a couple of other classes involved) part of the code;

public String listAll()
{
    itr = arrBok.iterator();
    while (itr.hasNext())
    {
        i++;
    }
    return "lol";
}

This code does nothing useful, but I just want to see if it can iterate through it successfully.

What I have tried so far;

• Tested if the bokArr (ArrayList) is empty, which it’s not. It has 4 objects inside of it.

• Return the toString() method of the itr, with the following result;

java.util.AbstractList$Itr@173a10f // <– not sure if this would be relevant to anything

• return itr.next().toString(); <– // which seems to return the first object in the array, does that make sense?

Answer 1

That code as quoted won’t compile, you’re missing a couple of declarations. But I think I get the gist.

hasNext tells you that the iterator has a next value, but doesn’t take you to it. To do that, you use next. So that is an endless loop because you’re never calling next.

With any recent compiler, you can use the much simpler notation for this:

for (Object book : arrBok) {
    // ...do something with 'book' (or just increment your counter)...
}

That iterates through the collection (list, in this case) for you.