Java: How to find Unique Values in ArrayList (using TreeSet, HashSet)

This tutorial gives you simple way to find unique values in ArrayList using TreeSet and HashSet. HashSet is much faster than TreeSet (constant-time versus log-time for most operations like add, remove and contains) but offers no ordering guarantees like TreeSet.

If you have any of below questions then you are at right place.

• Get unique values from arraylist in java
• How to get unique values in List
• Create an ArrayList of unique values
• How to Remove Duplicates from ArrayList in Java
• Distinct value from ArrayList in JAVA
• How to create an ArrayList of unique values in Java

Let’s get started:

• Create a class CrunchifyUniqueArrayList.java.

Here is a what we will use in our program:

• HashSet
• TreeSet
• Create your own Distinct Utility: crunchifyPrintUniqueValues();

package crunchify.com.tutorials;

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

/**
 * @author Crunchify.com
 * How to find Unique Values in ArrayList.
 * Create your own utility to find unique elements in ArrayList.
 */

public class CrunchifyUniqueArrayList {

    public static void main(String[] args) {
        List<String> crunchifyStringList = Arrays.asList("Facebook", "Twitter", "Google", "Facebook", "Google", "Twitter", "Google");
        System.out.printf("\n====== Initial list: %s%n", crunchifyStringList);
        sortList(crunchifyStringList);

        // Let's create our own utility to find unique elements in ArrayList :)
        crunchifyPrintUniqueValues(crunchifyStringList, crunchifyStringList.size());
    }

    static void crunchifyPrintUniqueValues(List<String> crunchifyArray, int crunchifySize) {
        // iterate through all elements
		System.out.print ("\n\n====== From crunchifyPrintUniqueValues() Method: ");
        for (int externalLoop = 0; externalLoop < crunchifySize; externalLoop++) {
            int internalLoop;

            for (internalLoop = 0; internalLoop < externalLoop; internalLoop++)
                if (crunchifyArray.get(externalLoop) == crunchifyArray.get(internalLoop))
                    break;

            // Print only if it's not printed before
            if (externalLoop == internalLoop)
                System.out.print(crunchifyArray.get(externalLoop) + " ");
        }
    }

    public static void sortList(List<String> myList) {

        // HashSet() constructs a new set containing the elements in the specified collection.
        // The HashMap is created with default load factor (0.75) and an initial capacity sufficient to contain the elements in the specified collection.
        Set<String> hashSetList = new HashSet<String>(myList);
        System.out.printf("\n====== Unique values using HashSet: %s", hashSetList);

        // TreeSet() Constructs a new tree set containing the elements in the specified collection, sorted according to the natural ordering of its elements.
        // All elements inserted into the set must implement the Comparable interface.
        // Furthermore, all such elements must be mutually comparable: e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the set.
        Set<String> treeSetList = new TreeSet<String>(myList);
        System.out.printf("\n====== Unique values using TreeSet: %s", treeSetList);
    }
}

Output:

Here is a Eclipse Console Output. Just run an application as a Java program.

====== Initial list: [Facebook, Twitter, Google, Facebook, Google, Twitter, Google]

====== Unique values using HashSet: [Google, Twitter, Facebook]
====== Unique values using TreeSet: [Facebook, Google, Twitter]

====== From crunchifyPrintUniqueValues() Method: Facebook Twitter Google 
Process finished with exit code 0

Let me know if you face any issue running this java program.