Lista

public class ListaLigada {

    private class Node {

        public int element;
        public Node next, previous;

        public Node(int nValue) {
            element = nValue;
            next = null;
            previous = null;
        }
    }

    private Node head;
    private int tamanho;

    public ListaLigada() {
        head = null;
        tamanho = 0;
    }

    public boolean isEmpty() {
        return head == null;
    }

    public boolean remove(int i) {
        if (isEmpty()) {
            return false;
        }

        Node delete = head, previous = null;
        while (delete != null && delete.element != i) {
            previous = delete;
            delete = delete.next;
        }

        if (delete == head) {
            head = head.next;
            head.previous = null;
        } else if (delete != null) {
            previous.next = delete.next;
            delete.next.previous = previous;
        } else if (delete == null) {
            return false;
        }

        tamanho--;
        return true;
    }

    public boolean add(int i) {
        Node newNode = new Node(i);
        Node actual = head, previous = null;

        while (actual != null && i > actual.element) {
            previous = actual;
            actual = actual.next;
        }

        if (previous == null) {
            newNode.next = head;
            head = newNode;
        } else {
            if (actual == null) {
                newNode.previous = previous;
                previous.next = newNode;
            } else {
                newNode.next = actual;
                actual.previous = newNode;
                previous.next = newNode;
                newNode.previous = previous;
            }
        }
        tamanho++;
        return true;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        Node actual = head;
        if (head == null) {
            return "Lista vazia!";
        }

        sb.append("Lista:\n");

        while (actual.next != null) {
            sb.append("" + actual.element + " -> ");
            actual = actual.next;
        }
        sb.append("" + actual.element + "\n");

        sb.append("\nLista reversa:\n");

        while (actual.previous != null) {
            sb.append("" + actual.element + " <- ");
            actual = actual.previous;
        }
        sb.append("" + actual.element + "\n");

        return sb.toString();
    }

    public static void main(String[] args) {
        ListaLigada ll = new ListaLigada();
        ll.add(5);
        ll.add(7);
        ll.add(3);
        ll.add(4);
        ll.remove(5);
        System.out.println(ll);
    }
}