CopyOnWriteArrayList difference with normal ArrayList

CopyOnWriteArrayList was introduced in JDK5, Which will be used to avoid the java.util.ConcurrentModificationException while modifying List by multiple threads or inside loop.

below sample will show the difference.

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Find Number of duplicates present in a ArrayList

To find the number of occurrences of duplicate integer present in List, first we will create temp List which will have no duplicates and then use collection frequecy() function to get the occurrence of duplicate number in original list.

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