Double nested for loop iteration (ArrayList)

Question

I have a system that involves loading 'PlayerValue' Objects. The objects are formatted as such: [Header] value. I have these saved in a text file and whenever I save or read from the file, I want to remove duplicate headers. So I did this:

first, I load all of the PlayerValues from the file into an ArrayList called 'array', then:

for (PlayerValue v : array) {
            for (PlayerValue v1 : array) {
                if (v1.header.equals(v.header)) {
                    array.remove(v1);
                }
            }
        }

Here you can see, it goes through each item of the array, then for each item, it searches the array again for the same header.

This would effectively remove duplicate headers, except for the fact that it throws a ConcurrentModificationException.

Any help for a work around?

Use a Set such as a HashSet rather than an ArrayList. Sets do not allow duplicates. Otherwise to remove from a collection while iterating, use an Iterator. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Oct 12, 2013 at 21:31
I could deal with duplicate entries, but two PlayerValues could have the same header with different values (thus making them unequal) and the ArrayList.contains method would ignore it. — zfollette
– zfollette, Commented Oct 12, 2013 at 21:34
@HovercraftFullOfEels The only issue is that he wants to remove duplicates based on some attribute, not just based on whether the objects are equal. — arshajii
– arshajii, Commented Oct 12, 2013 at 21:35

arshajii · Accepted Answer · 2013-10-12 21:42:02Z

2

Even if this worked, it would be a bad way to remove duplicates. A better option would be to have a Map<Header, PlayerValue>:

Map<String, PlayerValue> map = new HashMap<>();

for (PlayerValue v : array)
    map.put(v.header, v);

Now you can iterate through this map's entries, which will not contain duplicate keys (headers):

array.clear();

for (Entry<?, PlayerValue> e : map.entrySet())
    array.add(e.getValue());

edited Oct 12, 2013 at 21:42

answered Oct 12, 2013 at 21:33

arshajii

130k26 gold badges246 silver badges293 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

zfollette Over a year ago

Header isn't a separate object, it is an attribute of PlayerValue.

arshajii Over a year ago

@LegendOfFailure What is it, a String?

zfollette Over a year ago

Yes, it is. so you couldn't use 'Header' in the Object input of a Map<>

zfollette Over a year ago

Thats what I was doing, I completely forgot about HashMap.

zfollette Over a year ago

If I wanted to go further, I could edit the rest of the method to use only the map, instead of the ArrayList

|

Collectives™ on Stack Overflow

Double nested for loop iteration (ArrayList)

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related