Find Unique Elements In List Java

Chapter: Miscellaneous Last Updated: 07-10-2023 07:15:01 UTC

Program:

            /* ............... START ............... */
                
// Using a Set:

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class UniqueElementsInList {
    public static void main(String[] args) {
        List<Integer> myList = new ArrayList<>();
        myList.add(1);
        myList.add(2);
        myList.add(2);
        myList.add(3);
        myList.add(4);
        myList.add(4);
        
        Set<Integer> uniqueSet = new HashSet<>(myList);
        
        System.out.println("Unique elements in the list: " + uniqueSet);
    }
}


// Using a LinkedHashSet (Preserving Order):

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

public class UniqueElementsInList {
    public static void main(String[] args) {
        List<Integer> myList = new ArrayList<>();
        myList.add(1);
        myList.add(2);
        myList.add(2);
        myList.add(3);
        myList.add(4);
        myList.add(4);
        
        Set<Integer> uniqueSet = new LinkedHashSet<>(myList);
        
        System.out.println("Unique elements in the list (preserving order): " + uniqueSet);
    }
}

// Using Java Streams (Java 8 and later):

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class UniqueElementsInList {
    public static void main(String[] args) {
        List<Integer> myList = new ArrayList<>();
        myList.add(1);
        myList.add(2);
        myList.add(2);
        myList.add(3);
        myList.add(4);
        myList.add(4);
        
        List<Integer> uniqueList = myList.stream().distinct().collect(Collectors.toList());
        
        System.out.println("Unique elements in the list: " + uniqueList);
    }
}


                /* ............... END ............... */
        

Notes:

  • In first program You can use a Set data structure to store the unique elements from the list because a Set does not allow duplicate values.
  • In second program if you want to maintain the order of elements while removing duplicates, you can use a LinkedHashSet, which is an ordered version of the Set.
  • In last program we have used Java streams to filter out the unique elements from a list:
  • Any of these methods will give you a list or set containing only the unique elements from the original list, depending on your preference for preserving order or not.
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