Exception in thread "main" java.util.ConcurrentModificationException - go through the set and delet

Question

Pls help me with this problem. I have Graph represent by Structure HashMap> graf; and i need to go throught that hashmap and set and remove some edges. How can i do that ? code give me this exception

Exception in thread "main" java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
        at java.util.HashMap$KeyIterator.next(Unknown Source)


      public String vratCestu() {
            String vrat = "";
            for(String s: this.graf.keySet()){
                if (this.graf.get(s).size() != 0)

                    for(String k : this.graf.get(s)){
                            this.graf.get(s).remove(k);
                            this.graf.get(k).remove(s);
                            vrat += k + "; ";

                    }
                }
                return vrat;
            }

possible duplicate of ConcurrentModificationException and a HashMap — Peter Lawrey
– Peter Lawrey, Commented Apr 23, 2014 at 13:40

Mubin · Accepted Answer · 2014-04-23 13:35:10Z

1

Instead of enhanced for loop for(String s: this.graf.keySet()), use an Iterator You cannot modify the collection while iterating over it with the use of enhanced for loop.

answered Apr 23, 2014 at 13:35

Mubin

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2 Comments

user3423578 Over a year ago

i am beginner in java pls can u write me an exaple how can i do it ?

Mubin Over a year ago

Refer the link that @peter-lawrey has suggested in his comment

Denis Kulagin · Accepted Answer · 2014-04-23 13:35:35Z

0

You cannot modify your HashSet directly while iterating over.

answered Apr 23, 2014 at 13:35

Denis Kulagin

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