Remove question wtih iterator

Question about the task

Set of cats

Java Syntax, Level 8, Lesson 11

Under discussion

Why can't I pass the test when I remove a cat with this code:

Iterator<Cat> iterator = cats.iterator();
        while (iterator.hasNext()) {
            Cat cat = iterator.next();
            if (cat.name.equals("Gringasho"))
                iterator.remove();
        }

But when I use a for each loop it passed the test.

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Renat Mukhametshin

Level 16 , Pervouralsk, Russain Federation

8 May 2019, 09:58

if you want to remove one cat: you can use iterator for this problem -

cats.remove(cats.iterator().next());

this code will remove the first cat that iterator return

Guadalupe Gagnon

Level 37 , Tampa, United States

20 January 2019, 17:17

https://stackoverflow.com/questions/223918/iterating-through-a-collection-avoiding-concurrentmodificationexception-when-re

Multivac

Level 13 , Lima, Perú

20 January 2019, 20:07

The link most voted answers say I should use iterator instead of a for loop. That's why I am so confused: I had to used the for loop in order to pass the test, but when I used the Iterator it didn't pass it. Even though I run it and it works fine, without ConcurrentModificationException.

Guadalupe Gagnon

Level 37 , Tampa, United States

21 January 2019, 14:37

There are some quirks in the verification system where superfluous code can fail what should otherwise be passable. The people at CodeGym are always fixing things every update (in my experience so far). Looking at the task and the code that you posted, the task only calls for you to make a blank cat class, the proper code would be:

public static class Cat {
}

I see that you have a name property in you cat class. I couldn't tell you if this was or was not causing your problem, or i cant tell you why one method failed but the other passed. My original solution to the task had a foreach loop like so:

for(Cat x:cats){
   cats.remove(x);
   break;
}

Guadalupe Gagnon

Level 37 , Tampa, United States

9 May 2019, 16:27

@ Ungureanu: The tasks calls for you to use a Set. HashSets do not allow you to access individual indices as Lists do, so the code you shared would work if the Set was of type Integer and contained 0, like this:

HashSet<Integer> temp = new HashSet<>();
temp.add(1);
temp.add(2);
temp.add(0);
temp.remove(0);
System.out.println(temp);

This would output "[1, 2]" because it removed 0 from the set and not the first thing added to the set. The point here is that cats.remove(0); will not do anything because you need to pass it a Cat object to remove but you are trying to pass it an int. In my code above, my foreach loop breaks after the first iteration so that it only removes 1 value.