Removing elements from collections in java

in this tutorial lets discuss how to remove objects from collections list,Maps for the tutorial uses Array List

everybody knows how to iterate over a list or map my  .even though lots of way are there my favorite was for each. to iterate over a List of String

for(String iter:listname){

}

 so if we try to modify that is add or modify while iterating over it will throw concurrent modification exception So how to modify a collection while we iterate over it

ok  here we have a list

    

List<String> database = new ArrayList<String>();
        database.add("mysql");
        database.add("oracle");
        database.add("postgrade");
        database.add("mongodb");
        database.add("couchdb");

 there is two ways to remove a element while iterating over it 

1. iterating for loop backwards and removing them

for (int i = database.size() - 1; i >= 0; i--) {
            System.out.println("inside for loop" + database.get(i));
            if (database.get(i).equals("mongodb")) {
                System.out.println("sorry bitches you dont belong here you need to be kicked out");
                database.remove(i);
            }
        }

2nd way using the iterator

while (iterator.hasNext()) {
            String dbname = iterator.next();
            System.out.println("the iterator element is" + dbname);
            if (dbname.equals("couchdb")) {
                System.out.println("YOU too dont belong here you too will be kicked out");
                iterator.remove();
            }
        }

and the output