I'm trying to remove a particular element from Arraylist, it throws an ConcurrentModificationException
ArrayList<String> ar = new ArrayList<String>();
ar.add("a");
ar.add("b");
ar.add("c");
ar.add("a");
ar.add("e");
for(String st: ar){
System.out.println("st="+st);
if(st.equals("a")){
ar.remove(st);
}
}
any comments, what am I doing wrong?
Only remove an element from the array while iterating by using Iterator.remove().
The line for(String st: ar) { is a bit misleading. You're actually creating an iterator behind the scenes which is being used for this iteration. If you need to remove elements from within the iteration, you need to explicitly use an iterator so that you can call iterator.remove().
ArrayList<String> ar = new ArrayList<String>();
ar.add("a");
ar.add("b");
ar.add("c");
ar.add("a");
ar.add("e");
Iterator<String> it = ar.iterator();
while (it.hasNext()) {
String st = it.next();
System.out.println("st="+st);
if (st.equals("a")) {
it.remove();
}
}
Iterator.remove() to delete an element from an ArrayList while using ArrayList.forEach()?you are modifing the array you are iterating on. I suggest you to use the Iterator to do similar things.
remove() method, so what maVVamaldo said is good advice if it is interpreted as "use an explicit operator", since that would allow safe deletion via Iterator.remove().You're removing an element from a collection while you're iterating over that collection, without using the iterator to do it. Don't do that. There are lots of alternatives, primarily:
Use indexes instead (get, remove(int)) being careful about your counts so that you don't skip over items
for (int i = 0; i < ar.size(); i++) {
String st = ar.get(i);
System.out.println("st="+st);
if(st.equals("a")) {
ar.remove(i);
i--; // We want to use this index again
}
}
Build up a collection of items to remove, then remove them all afterwards
List<String> elementsToRemove = new ArrayList<String>();
for(String st: ar){
System.out.println("st="+st);
if(st.equals("a")){
elementsToRemove.add(st);
}
}
ar.removeAll(elementsToRemove);
Remove using the iterator, if the iterator supports removal (as ArrayList's does)
for (Iterator<String> it = ar.iterator(); it.hasNext(); ) {
String st = it.next();
System.out.println("st="+st);
if(st.equals("a")) {
it.remove();
}
}
