Using Java

In this method, we use HashSet to remove duplicate elements from an ArrayList. As you know, HashSet doesn’t allow duplicate elements. We use this property of HashSet to remove duplicate elements from already constructed ArrayList. But, there is one disadvantage of this method. That is, it erases the insertion order of ArrayList elements. That means, after removing the duplicate elements, elements will not be in the insertion order. Let’s see one example.

import java.util.ArrayList;
import java.util.HashSet;
 
public class MainClass
{
    public static void main(String[] args)
    {
        //Constructing An ArrayList
 
        ArrayList<String> listWithDuplicateElements = new ArrayList<String>();
 
        listWithDuplicateElements.add("JAVA");
 
        listWithDuplicateElements.add("J2EE");
 
        listWithDuplicateElements.add("JSP");
 
        listWithDuplicateElements.add("SERVLETS");
 
        listWithDuplicateElements.add("JAVA");
 
        listWithDuplicateElements.add("STRUTS");
 
        listWithDuplicateElements.add("JSP");
 
        //Printing listWithDuplicateElements
 
        System.out.print("ArrayList With Duplicate Elements :");
 
        System.out.println(listWithDuplicateElements);
 
        //Constructing HashSet using listWithDuplicateElements
 
        HashSet<String> set = new HashSet<String>(listWithDuplicateElements);
 
        //Constructing listWithoutDuplicateElements using set
 
        ArrayList<String> listWithoutDuplicateElements = new ArrayList<String>(set);
 
        //Printing listWithoutDuplicateElements
 
        System.out.print("ArrayList After Removing Duplicate Elements :");
 
        System.out.println(listWithoutDuplicateElements);
    }
}

Output:-
ArrayList With Duplicate Elements :[JAVA, J2EE, JSP, SERVLETS, JAVA, STRUTS, JSP]
ArrayList After Removing Duplicate Elements :[JAVA, SERVLETS, JSP, J2EE, STRUTS]