MyList5 + Iterator

Launcher.java

package lesson7.mylist;

public class Launcher {

    public static void main(String[] args) {

        SimpleLinkedList sl = new SimpleLinkedList();

        sl.addFirst("object1");
        sl.addFirst("object2");
        sl.addFirst("object3");
        sl.addLast("object4");
        sl.addLast("object5");
        sl.addAfter("object4", "fff");
        sl.addAfter("object5", "aaa");
        sl.addLast("object4");

        for (Object o : sl) {
            System.out.println(o);
        }
    }
}

SimpleLinkedList.java

package lesson7.mylist;


import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;

public class SimpleLinkedList implements Iterable<Object> {

    private Node root;
    private int size;

    public SimpleLinkedList() {
        size = 0;
    }

    public void addFirst(Object o) {

        Node node = new Node();
        node.object = o;
        if(root != null) {
            node.node = root;
        }
        root = node;

        size++;
    }

    public void addLast(Object o) {

        Node nodeNew = new Node();
        nodeNew.object = o;

        if (root != null) {
            Node gapNode = root.node;
            Node gap = root.node;

            while (gapNode != null) {
                gap = gapNode;
                gapNode = gapNode.node;
            }

            gap.node = nodeNew;
            size++;
        }
        else addFirst(o);
    }

    public void addAfter(Object after, Object newObj) throws IllegalStateException {

        Node nodeNew = new Node();
        nodeNew.object = newObj;

        if (root != null) {
            Node gapNode = root.node;
            Node gap = root.node;
            boolean isTrueObject = false;

            while (gapNode != null) {

                if (gapNode.object.equals(after)) {
                    isTrueObject = true;
                    break;
                }
                gap = gapNode;
                gapNode = gapNode.node;
            }

            if (isTrueObject == false) {
                throw new IllegalStateException("There is not such element");
            }
            else if (gap.node == null) {
                addLast(newObj);
            }
            else {
                Node afterNew = gapNode.node;
                gapNode.node = nodeNew;
                nodeNew.node = afterNew;

                size++;
            }
        }
        else addFirst(newObj);
    }

    public int getSize() {
        return size;
    }

    public void printList(Iterator iterator) {

        while(iterator.hasNext()) {
            System.out.println(iterator.next());
        }

    }

    @Override
    public Iterator<Object> iterator() {

        return new SLLIterator();
    }

    private class Node {

        private Object object;
        private Node node;

        public Node() {
        }
    }

    private class SLLIterator implements Iterator<Object> {

        private Node n;

        public SLLIterator() {
            n = new Node();
            n.node = root;
        }

        @Override
        public boolean hasNext() {

            if (n.node != null) {
                return true;
            }
            else {
                return false;
            }
        }

        @Override
        public Object next() {

            if (hasNext()) {
                n = n.node;
                return n.object;
            }
            else {
                throw new NoSuchElementException();
            }
        }

        @Override
        public void remove() {

        }
    }
}