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Get Unique Values from ArrayList in Java

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  • Last Updated : 11 Dec, 2020

Let’s see how to get unique values from ArrayList. Convert ArrayList to HashSet to insert duplicate values in ArrayList but on the other hand, HashSet is not allowing to insert any duplicate value. While converting ArrayList to HashSet all the duplicate values are removed and as a result, unique values are obtained.

Example:

INPUT : ArrayList = [a, b, c, b, d, a, c]
OUTPUT: Unique = [a, b, c, d]

INPUT : ArrayList = [1, 5, 2, 4, 3, 4, 5]
OUTPUT: Unique = [1, 2, 3, 4, 5]

Approach:

  • Create a ArrarList.
  • Add elements in ArrayList.
  • Create HashSet and pass in HashSet constructor.
  • Print HashSet object.

Below is the implementation of the above approach:

Java




// Get Unique Values from ArrayList in Java
import java.util.ArrayList;
import java.util.HashSet;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        // Create ArrayList
        ArrayList<String> ArrList = new ArrayList<String>();
  
        // add values in ArrayList
        ArrList.add("a");
        ArrList.add("b");
        ArrList.add("c");
        ArrList.add("b");
        ArrList.add("d");
        ArrList.add("a");
        ArrList.add("c");
  
        // display original ArrayList
        System.out.println("Original ArrayList is : "
                           + ArrList);
  
        // convert ArrayList to HastSet.
        HashSet<String> hset = new HashSet<String>(ArrList);
  
        // display HastSet
        System.out.println("ArrayList Unique Values is : "
                           + hset);
    }
}


Output

Original ArrayList is : [a, b, c, b, d, a, c]
ArrayList Unique Values is : [a, b, c, d]

Time Complexity: O(n), where n is the length of the original ArrayList.

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