Java LinkedHashSet retainAll() Method

The LinkedHashSet.retainAll() method in Java is used to retain only the elements in the LinkedHashSet that are contained in the specified collection. 

Table of Contents

1. Introduction
2. retainAll Method Syntax
3. Examples
   • Retaining Common Elements in LinkedHashSet
   • Handling Collections with No Common Elements
4. Conclusion

Introduction

The LinkedHashSet.retainAll() method is a member of the LinkedHashSet class in Java. It allows you to modify the LinkedHashSet so that it retains only those elements that are also contained in the specified collection. This method is useful for finding the intersection of two collections.

retainAll() Method Syntax

The syntax for the retainAll method is as follows:

public boolean retainAll(Collection<?> c)

• The method takes a single parameter c of type Collection<?>, which represents the collection containing elements to be retained in the LinkedHashSet.
• The method returns a boolean value:
  • true if the LinkedHashSet changed as a result of the call.
  • false if the LinkedHashSet did not change (i.e., it already contained only the elements in the specified collection).

Examples

Retaining Common Elements in LinkedHashSet

The retainAll method can be used to retain only the elements in the LinkedHashSet that are also in the specified collection.

Example

import java.util.ArrayList;
import java.util.LinkedHashSet;

public class RetainAllExample {
    public static void main(String[] args) {
        // Creating a LinkedHashSet of Strings
        LinkedHashSet<String> animals = new LinkedHashSet<>();

        // Adding elements to the LinkedHashSet
        animals.add("Lion");
        animals.add("Tiger");
        animals.add("Elephant");

        // Creating a list of animals to retain
        ArrayList<String> animalsToRetain = new ArrayList<>();
        animalsToRetain.add("Lion");
        animalsToRetain.add("Giraffe");

        // Retaining only the elements that are also in the list
        boolean isChanged = animals.retainAll(animalsToRetain);

        // Printing the result of retainAll and the LinkedHashSet
        System.out.println("Was the LinkedHashSet changed? " + isChanged);
        System.out.println("LinkedHashSet after retainAll: " + animals);
    }
}

Output:

Was the LinkedHashSet changed? true
LinkedHashSet after retainAll: [Lion]

Handling Collections with No Common Elements

If the specified collection has no common elements with the LinkedHashSet, the retainAll method will remove all elements from the set.

Example

import java.util.ArrayList;
import java.util.LinkedHashSet;

public class RetainAllNoCommonExample {
    public static void main(String[] args) {
        // Creating a LinkedHashSet of Strings
        LinkedHashSet<String> animals = new LinkedHashSet<>();

        // Adding elements to the LinkedHashSet
        animals.add("Lion");
        animals.add("Tiger");
        animals.add("Elephant");

        // Creating a list of animals to retain with no common elements
        ArrayList<String> animalsToRetain = new ArrayList<>();
        animalsToRetain.add("Giraffe");
        animalsToRetain.add("Monkey");

        // Retaining only the elements that are also in the list
        boolean isChanged = animals.retainAll(animalsToRetain);

        // Printing the result of retainAll and the LinkedHashSet
        System.out.println("Was the LinkedHashSet changed? " + isChanged);
        System.out.println("LinkedHashSet after retainAll: " + animals);
    }
}

Output:

Was the LinkedHashSet changed? true
LinkedHashSet after retainAll: []

Conclusion

The LinkedHashSet.retainAll() method in Java provides a way to retain only those elements in a LinkedHashSet that are contained in another collection. By understanding how to use this method, you can efficiently find the intersection of two collections and manage the elements in your sets. This method is useful for filtering collections based on specific criteria, making it a valuable tool for collection management in your Java applications.