Java : AbstractSet with Examples

class MySet extends AbstractSet<String> {

    private final String[] elements;

    MySet(String e1, String e2, String e3) {
        if (Objects.equals(e1, e2) || Objects.equals(e1, e3) || Objects.equals(e2, e3)) {
            throw new IllegalArgumentException("duplicate element");
        }

        elements = new String[]{e1, e2, e3};
    }

    @Override
    public Iterator<String> iterator() {
        return new Iterator<>() {
            private int index;

            @Override
            public boolean hasNext() {
                return elements.length != index;
            }

            @Override
            public String next() {
                final var value = elements[index];
                index++;
                return value;
            }
        };
    }

    @Override
    public int size() {
        return elements.length;
    }
}

final var set = new MySet("aaa", "bbb", "ccc");
System.out.println(set); // [aaa, bbb, ccc]
System.out.println(set.size()); // 3

System.out.println("-- elements --");
for (final var element : set) {
    System.out.println(element);
}

// Result
// ↓
//-- elements --
//aaa
//bbb
//ccc

AbstractSet ()

Sole constructor.

For invocation by subclass constructors, typically implicit. Therefore, the code example is omitted.

boolean equals (Object o)

Compares the specified object with this set for equality.

final AbstractSet<String> set = new HashSet<>();
Collections.addAll(set, "a", "b", "c");
System.out.println(set); // [a, b, c]

System.out.println(set.equals(Set.of("a"))); // false
System.out.println(set.equals(Set.of("a", "b"))); // false
System.out.println(set.equals(Set.of("a", "b", "c"))); // true
System.out.println(set.equals(Set.of("c", "b", "a"))); // true

final AbstractSet<String> set = new HashSet<>();
Collections.addAll(set, "a", "b", "c");
System.out.println(set); // [a, b, c]

final Set<String> hashSet = new HashSet<>(set);
System.out.println(hashSet); // [a, b, c]
System.out.println(set.equals(hashSet)); // true

final Set<String> treeSet = new TreeSet<>(set);
System.out.println(treeSet); // [a, b, c]
System.out.println(set.equals(treeSet)); // true

final var list = new ArrayList<>(set);
System.out.println(list); // [a, b, c]
System.out.println(set.equals(list)); // false

int hashCode ()

Returns the hash code value for this set.

final AbstractSet<String> set1 = new HashSet<>();
Collections.addAll(set1, "a", "b", "c");
System.out.println(set1.hashCode()); // 294

final AbstractSet<Integer> set2 = new HashSet<>();
Collections.addAll(set2, 1, 2, 3);
System.out.println(set2.hashCode()); // 6

final AbstractSet<String> set1 = new LinkedHashSet<>();
set1.add("a");
set1.add("b");
set1.add("c");

System.out.println(set1); // [a, b, c]
System.out.println(set1.hashCode()); // 294

final AbstractSet<String> set2 = new LinkedHashSet<>();
set2.add("c");
set2.add("b");
set2.add("a");

System.out.println(set2); // [c, b, a]
System.out.println(set2.hashCode()); // 294

boolean removeAll (Collection<?> c)

Removes from this set all of its elements that are contained in the specified collection (optional operation).

final var src = Set.of("a", "b", "c");

{
    final AbstractSet<String> set = new HashSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of())); // false
    System.out.println(set); // [a, b, c]
}
{
    final AbstractSet<String> set = new HashSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("a"))); // true
    System.out.println(set); // [b, c]
}
{
    final AbstractSet<String> set = new HashSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("a", "b"))); // true
    System.out.println(set); // [c]
}
{
    final AbstractSet<String> set = new HashSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("b", "a"))); // true
    System.out.println(set); // [c]
}
{
    final AbstractSet<String> set = new HashSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("a", "b", "c"))); // true
    System.out.println(set); // []
}
{
    final AbstractSet<String> set = new HashSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("X", "Y"))); // false
    System.out.println(set); // [a, b, c]
}
{
    final AbstractSet<String> set = new HashSet<>(src);
    System.out.println(set); // [a, b, c]

    System.out.println(set.removeAll(Set.of("a", "X"))); // true
    System.out.println(set); // [b, c]
}

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, retainAll, toArray, toArray, toString

Please see the link below.

• Java API Examples : AbstractCollection

parallelStream, removeIf, stream, toArray

Please see the link below.

• Java API Examples : Collection

forEach

Please see the link below.

• Java API Examples : Iterable

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, retainAll, size, spliterator, toArray, toArray

Please see the link below.

• Java API Examples : Set