How to Prevent the Addition of Duplicate Elements to the Java ArrayList?

Widely used Java ArrayLists are data structures that offer dynamic arrays, enabling simple element manipulation. It is sometimes necessary to stop duplicate elements from being added to an ArrayList, though. Duplicate parts can cause your programme to behave unexpectedly, produce erroneous results, and use wasteful algorithms. This article will examine two methods to avoid adding duplicate components to a Java ArrayList, arming you with the information and resources you need to maintain data integrity and write cleaner code.

Multiple disadvantages may result from adding duplicate elements to an array list. First, it might result in redundant data, which would use up more memory and perhaps have an effect on performance. If duplicate items are not appropriately managed, they might potentially lead to inaccurate calculations or analysis. Duplicate entries, for instance, can result in conflicts and inaccurate results when searching, sorting, or performing other actions on the ArrayList when using unique IDs or keys.

We will examine two practical approaches to stop the addition of duplicate elements to a Java ArrayList to allay these worries. These methods will assist you in preserving the integrity of your data, enhancing the effectiveness of your code, and guaranteeing accurate outcomes for your applications.

Approaches

To prevent duplicate elements in Java ArrayList, we can follow the two methods:

• Utilizing the contains() method.

• Utilizing HashSet for Deduplication.

Let us look into both approaches:-

Approach-1: Utilizing the contains() method.

The first way involves determining whether an element already exists in the list before adding it using the contains() method offered by the ArrayList class.

Algorithm

The steps to prevent the addition of duplicate elements of the Java ArrayList are as follows:

Step-1: Make an object called ArrayList.

Step-2: Utilizing the contains() method, determine whether the element to be added already exists in the list.

Step-3: Utilize the add() method to add the element to the ArrayList if it isn't already there.

Step-4: As needed, repeat steps 2 as well as 3.

Example

import java.util.ArrayList;

public class Main {

    public static void main(String[] args) {
        ArrayList<String> myList = new ArrayList<>();

        addUniqueElement(myList, "Pen");
        addUniqueElement(myList, "Book");
        addUniqueElement(myList, "Pen"); // This will not be added
        addUniqueElement(myList, "Pencil");
        System.out.println(myList); 
    }

    private static void addUniqueElement(ArrayList<String>list, String element) {
        if (!list.contains(element)) {
            list.add(element);
        }
    }
}

Output

[Pen, Book, Pencil]

Approach-2: Utilizing the HashSet for Deduplication.

Utilizing a HashSet, a collection that forbids duplicate elements constitutes the second strategy. By adding members to the HashSet and then copying the HashSet back to the ArrayList, we can take advantage of this property.

Algorithm

The steps to prevent the addition of duplicate elements of the java ArrayList are as follows:

Step-1: Make a HashSet object and an ArrayList.

Step-2: Go through the elements one by one.

Step-3: Verify the HashSet to see if the element is already there.

Step-4: Add it to the HashSet if it doesn't already exist.

Step-5: Clear the ArrayList after going through each entry in turn.

Step-6: Utilize the addAll() function to return the elements from the HashSet to the ArrayList.

Example

//import the required package
import java.util.ArrayList;
import java.util.HashSet;

public class Main {

    public static void main(String[] args) {
        ArrayList<String> myList = new ArrayList<>();
//Invoke addUniqueElements()
        addUniqueElements(myList, "Pen");
        addUniqueElements(myList, "Pencil");
        addUniqueElements(myList, "Pen"); // This will not be added
        addUniqueElements(myList, "Book");
//Display unique elements
        System.out.println(myList);
    }

    private static void addUniqueElements(ArrayList<String> list, String element) {
        if (!list.contains(element)) {
            list.add(element);
        }
    }
}

Output

[Pen, Pencil, Book]

Conclusion

This article looked at two methods for preventing the inclusion of duplicate elements in a Java ArrayList. You may make sure that your ArrayList only contains unique elements by using the contains() function or by using a HashSet for deduplication, which will increase the correctness and effectiveness of your code. You can select the strategy that best meets your demands based on your requirements and the volume of your data. When determining which approach to utilize, keep in mind the trade-offs between memory utilization, performance, and simplicity of implementation. By using these methods, you can optimize your ArrayList operations while maintaining data integrity.