How to Perform Intersection and Union Operations on ArrayLists in Java?

Intersecting and Uniting ArrayLists in Java

Question:

How to perform intersection and union operations on ArrayLists in Java? Extension to the question is regarding the applicability of ArrayLists for file filtering in the context of set theory.

Answer:

ArrayLists offer no built-in methods for intersection or union. A straightforward implementation is provided below:

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

public class ArrayListOperations {

    public static void main(String[] args) {
        List<string> list1 = new ArrayList(Arrays.asList("A", "B", "C"));
        List<string> list2 = new ArrayList(Arrays.asList("B", "C", "D", "E", "F"));

        System.out.println(intersection(list1, list2));
        System.out.println(union(list1, list2));
    }

    public static <t> List<t> intersection(List<t> list1, List<t> list2) {
        List<t> list = new ArrayList();

        for (T t : list1) {
            if (list2.contains(t)) {
                list.add(t);
            }
        }

        return list;
    }

    public static <t> List<t> union(List<t> list1, List<t> list2) {
        Set<t> set = new HashSet();

        set.addAll(list1);
        set.addAll(list2);

        return new ArrayList(set);
    }
}</t></t></t></t></t></t></t></t></t></t></string></string>

Regarding File Filtering:

Using ArrayLists for file filtering is appropriate if the number of files is relatively small. However, for larger datasets, considering a more efficient data structure like a HashSet or TreeSet would be beneficial for optimized runtime performance.

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