How to find Duplicate Entry of Elements (numbers) in ArrayList in java

How to find Duplicate Entry of Elements (numbers) in ArrayList in java

SOURCE : NumDuplicate.java

import java.util.ArrayList;
import java.util.List;

public class NumDuplicate {

	static void dups(List ls) {

		List lst = new ArrayList<>();

		for (Integer i : ls) {

			if (lst.contains(i)) {

				System.out.println("duplicate " + i);
			} else

				lst.add(i);

		}
	}

	public static void main(String[] args) {
		List ls = new ArrayList<>();
		for (int i = 0; i < 30; i++) {
			ls.add(i);
		}
		ls.add(15);
		ls.add(22);
		dups(ls);

	}

}

INPUT

number from 1 to 30 and 
added 15 and 22 as duplicate 

OUTPUT

 duplicate 15
duplicate 22

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