Java Linked List Implementation: Essential Methods

Java Linked List Implementation

Inserting Elements at Positions

public void insertPos() {
    if (isEmpty()) {
        throw new EmptyCollectionException("Lista");
    } else {
        LinearNode actual = first;
        LinearNode nuevo = null;
        int posActual = 1;
        while (actual != null) {
            nuevo = new LinearNode(posActual);
            nuevo.next = actual.next;
            actual.next = nuevo;
            actual = nuevo.next;
            nElements++;
            posActual++;
        }
    }
}

Skipping Iterator Implementation

private class SkippingIteratorImpl implements Iterator<T> {
    private Node<T> current;

    public SkippingIteratorImpl() {
        current = first;
        if (first != null) {
            current = first.next;
        }
    }

    @Override
    public boolean hasNext() {
        return (current != null);
    }

    @Override
    public T next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        T elemento = current.element;
        current = current.next;
        if (current != null) {
            current = current.next;
        }
        return elemento;
    }
}

Removing the Penultimate Element

public T eliminarPenult() throws EmptyCollectionException {
    T result;
    if (first == null) {
        throw new EmptyCollectionException("Lista vacia");
    } else if (first.next == null) {
        result = first.element;
        first = null;
    } else if (first.next.next == null) { // 2 elementos
        result = first.element;
        first = first.next;
    } else { // Tiene mas de dos elementos
        Node<T> antepenul = first;
        Node<T> penultimo = first.next;
        while (penultimo.next.next != null) {
            antepenul = antepenul.next;
            penultimo = penultimo.next;
        }
        result = penultimo.element;
        antepenul.next = penultimo.next;
    }
    return result;
}

Reordering the First Element

public void recolocaPrim() throws EmptyCollectionException {
    if (header == null) throw new EmptyCollectionException("");
    if (header != tail) {
        if (header.next == tail) {
            // Dos elementos
            tail = header;
            header = header.next;
            header.next = tail;
            header.previous = null;
            tail.previous = header;
            tail.next = null;
        } else {
            // Caso general
            DoubleNode aux = header;
            header = header.next;
            header.previous = null;
            DoubleNode penultimo = tail.previous;
            aux.next = tail;
            aux.previous = penultimo;
            tail.previous = aux;
            penultimo.next = aux;
        }
    }
}