MyList5 + addAfter()

Launcher.java

package lesson7.mylist;


public class Launcher {

    public static void main(String[] args) {

        SimpleLinkedList sl = new SimpleLinkedList();

        sl.addFirst("object1");
        sl.printList();
        sl.addFirst("object2");
        sl.printList();
        sl.addFirst("object3");

        sl.printList();
        System.out.println(sl.getSize());

        sl.addLast("object4");
        sl.printList();
        sl.addLast("object5");
        sl.printList();
        System.out.println(sl.getSize());

        sl.addAfter("object4", "fff");
        sl.printList();
        System.out.println(sl.getSize());

        sl.addAfter("object5", "aaa");
        sl.printList();
        System.out.println(sl.getSize());
    }
}

SimpleLinkedList.java

package lesson7.mylist;


public class SimpleLinkedList {

    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() {

        Node n = root;

        if (n == null) {
            System.out.println("List is empty");
        }

        else {
            while (n.node != null) {
                System.out.print(n.object + ", ");
                n = n.node;
            }
            System.out.println(n.object);
        }
    }

    private class Node {

        private Object object;
        private Node node;

        public Node() {
        }
    }
}