Delete entry from HashMap

Question

I have a HashMap:

public static Map<String, Set<String>> adjMap = new HashMap<String, Set<String>>();
adjMap.put(title, new HashSet<String>());
adjMap.get(title).add(cutTitle(graphLink));

Now I want do delete all entries from the values (HashSet), which does not contains as a key.

Here is my code so far:

for(String s: adjMap.keySet()){
    for(Set<String> s1: adjMap.values()){
        for(String s2: s1){
            if(!s.contains(s2)){
                s1.remove(s2);
            }
        }
    }
}

But I get an exception:

Exception in thread "main" java.util.ConcurrentModificationException

You are trying to modify the Hashset in Foreach loop apart from it's using it's own iterator. — Ankit Tripathi, Nov 16 '16 at 10:11

score 2 · Answer 1 · answered Nov 16 '16 at 10:11

2

Iterate your Map

Iterator it = adjMap.entrySet().iterator();
    while (it.hasNext())
    {
       Entry item = it.next();
       map.remove(item.getKey());
    }

answered Nov 16 '16 at 10:11

Sangram Badi

4,054
9
45
78

score 0 · Answer 2 · edited May 23 '17 at 11:53

0

I think for-each loops are not allowed to alter the iterated object. To remove entries you should use an iterator.

Compare to map-Iteration for an example.

edited May 23 '17 at 11:53

Community

1
1

answered Nov 16 '16 at 10:08

Jannek S.

365
3
16

score 0 · Answer 3 · answered Nov 16 '16 at 10:11

0

You can use ConcurrentHashMap instead, or create a copy of your HashMap and make any changes to the copy.

answered Nov 16 '16 at 10:11

D. Krauchanka

264
3
15

Delete entry from HashMap

3 Answers3