ArrayList<Integer> list = new ArrayList<>();
        Set<Integer> resultCrossing = new HashSet<>();
        list.addAll(A);
        list.addAll(B);

package Epam2;
public class Task4 {

    static Set<Integer> A = new HashSet<>();
    static Set<Integer> B = new HashSet<>();
    Random rand = new Random();

    void crossingMultiplicity() {
        ArrayList<Integer> list = new ArrayList<>();
        Set<Integer> resultCrossing = new HashSet<>();
        list.addAll(A);
        list.addAll(B);
        System.out.println(list);
    
        for(int i = 0; i < list.size(); i++){
            for(int j = 0; j < list.size(); j++){
                if(list.get(i)==list.get(j)){
                    resultCrossing.add(list.get(i));
                }
            }
        }
//        for (Integer n : list) {
//            for (Integer num : list) {
//                if (num == n) {
//                    resultCrossing.add(num);
//                }
//            }
//        }
        System.out.println("Пересечение множеств: " + resultCrossing + "\n");

    }
    void addMultiplicity() {
        for (int i = 0; i < 30; i++) {
            A.add(rand.nextInt(20));
            B.add(rand.nextInt(20));
        }
    }

    public static void main(String[] args) {
        Task4 task = new Task4();
        task.addMultiplicity();
        task.crossingMultiplicity();
    }
}