Java.Collections.Implement a symmetric difference of two collections using Collection methods (addAll(…), removeAll(…), retainAll(…)).

🔄 Let’s implement the symmetric difference of two collections in Java using only standard Collection methods like addAll(), removeAll(), and retainAll() — no custom loops, no streams, just pure Java Collections API.

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✅ What is symmetric difference?

The symmetric difference between two sets A and B is the set of elements that are in either A or B, but not in both:

A △ B = (A ∪ B) - (A ∩ B)

Or in Java terms:

(A + B) - (A.retainAll(B))

💡 Java Implementation:

import java.util.*;

public class SymmetricDifferenceExample {
    public static void main(String[] args) {
        Collection<String> setA = new ArrayList<>(List.of("apple", "banana", "cherry"));
        Collection<String> setB = new ArrayList<>(List.of("banana", "date", "cherry"));

        // Step 1: Union of A and B
        Collection<String> result = new ArrayList<>(setA);
        result.addAll(setB); // result = A ∪ B

        // Step 2: Intersection of A and B
        Collection<String> intersection = new ArrayList<>(setA);
        intersection.retainAll(setB); // intersection = A ∩ B

        // Step 3: Remove intersection from union to get symmetric difference
        result.removeAll(intersection);

        System.out.println("Symmetric Difference: " + result);
        // Output: [apple, date]
    }
}

🧠 Explanation:

Step	Collection	Contents
addAll()	result = A ∪ B	[apple, banana, cherry, banana, date, cherry]
retainAll()	intersection = A ∩ B	[banana, cherry]
removeAll()	result - intersection	[apple, date]

✔️ Duplicates will be handled correctly based on the underlying collection type (e.g. Set vs List).