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Java / List and its implementations

Java collections: How do I identify duplicate elements in a List?

Using HashSet implementation which doesn't allow duplicates can be used to identify the elements that are duplicate at the List. Set has a method add() that return boolean value true if the element already exists else returns false which can be used as a tracker to find the duplicate elements as shown below.

import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class DuplicateElements {

public static void main(String[] args) {
	String[] stringList = { "Javapedia.net", "Javapedia.net", "minim.tk", "weatherman.com" };
	List<String> listwithDuplicates = Arrays.asList(stringList);
	final Set<String> tempSet = new HashSet<>();
	final Set<String> duplicateElements = new HashSet<>();

	for (String element : listwithDuplicates) {
		if (!tempSet.add(element)) {
			duplicateElements.add(element);
		}
	}
	System.out.println(duplicateElements);
}

}

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