The way to Take away Duplicates from ArrayList in Java [Example]

ArrayList is the preferred implementation of the Checklist interface from Java’s Assortment framework, but it surely permits duplicates. Although there may be one other assortment referred to as Set which is primarily designed to retailer distinctive components, there are conditions while you obtain a Checklist like ArrayList in your code and it is advisable to make sure that it does not comprise any duplicate earlier than processing. Since with ArrayList you can’t assure uniqueness, there isn’t any different selection however to take away repeated components from ArrayList. 

There are a number of methods to do that, you’ll be able to observe the method we used for eradicating duplicates from array in Java, the place we loop by way of array and inserting every factor in a Set, which ensures that we discard duplicate as a result of Set does not enable them to insert, or you may as well use take away technique of ArrayList to do away with them, when you discovered that these are duplicates.

Btw, the only method to take away repeated objects from ArrayList is to repeat them to a Set e.g. HashSet after which copy it again to ArrayList. This can take away all duplicates with out writing any extra code.

One factor to famous is that, if unique order of components in ArrayList is vital for you, as Checklist maintains insertion order, it is best to use LinkedHashSet as a result of HashSet does not present any ordering assure.

If you’re utilizing deleting duplicates whereas iterating, be sure you use Iterator’s take away() technique and never the ArrayList one to keep away from ConcurrentModificationException.  On this tutorial we’ll see this method to take away duplicates.

Java Program to Take away duplicates from ArrayList

Right here is our pattern program to discover ways to take away duplicates from ArrayList. The steps adopted within the under instance are:

• Copying all the weather of ArrayList to LinkedHashSet. Why we select LinkedHashSet? As a result of it removes duplicates and maintains the insertion order.
• Emptying the ArrayList, you should use clear() technique to take away all components of ArrayList and begin contemporary. 
• Copying all the weather of LinkedHashSet (non-duplicate components) to the ArrayList. 

Please discover under the whole code :

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.Checklist;
import java.util.Set;


/**
 * Java Program to take away repeated components from ArrayList in Java.
 *
 * @creator WINDOWS 8
 */

public class ArrayListDuplicateDemo{
 
   
    public static void major(String args[]){
   
        // creating ArrayList with duplicate components
        Checklist<Integer> primes = new ArrayList<Integer>();
       
        primes.add(2);
        primes.add(3);
        primes.add(5);
        primes.add(7);  //duplicate
        primes.add(7);
        primes.add(11);
       
        // let's print arraylist with duplicate
        System.out.println("record of prime numbers : " + primes);
       
        // Now let's take away duplicate factor with out affecting order
        // LinkedHashSet will assured the order and because it's set
        // it is not going to enable us to insert duplicates.
        // repeated components will robotically filtered.
       
        Set<Integer> primesWithoutDuplicates
                   = new LinkedHashSet<Integer>(primes);
       
        // now let's clear the ArrayList in order that we are able to 
        // copy all components from LinkedHashSet
        primes.clear();
       
        // copying components however with none duplicates
        primes.addAll(primesWithoutDuplicates);
       
        System.out.println("record of primes with out duplicates : " + primes);
       
    }
 
}

Output
record of prime numbers : [2, 3, 5, 7, 7, 11]
record of primes with out duplicates : [2, 3, 5, 7, 11]