LinkedListDummyHead.java

public class LinkedListDummyHead<E> {

    private class Node {
        public E e;
        public Node next;

        public Node(E e, Node next) {
            this.e = e;
            this.next = next;
        }

        public Node(E e) {
            this(e, null);
        }

        public Node() {
            this(null, null);
        }

        @Override
        public String toString() {
            return e.toString();
        }
    }

    private Node dummyHead;
    int size;

    public LinkedListDummyHead() {
        dummyHead = new Node(null, null);
        size = 0;
    }

    // 获取链表中的元素个数
    public int getSize() {
        return size;
    }


    public boolean isEmpty() {
        return size == 0;
    }

    public void add(int index, E e) {
        if (index < 0 || index > size) {
            throw new IllegalArgumentException("Add failed. Illegal index.");
        }
        Node prev = dummyHead;
        for (int i = 0; i < index; i++) {
            prev = prev.next;
        }

        prev.next = new Node(e, prev.next);
        size++;
    }

    // 在链表头添加新的元素e
    public void addFirst(E e) {
//        Node node = new Node(e);
//        node.next = head;
//        head = node;
        add(0, e);

        size++;
    }

    // 在链表末尾添加新的元素e
    public void addLast(E e) {
        add(size, e);
    }


    // 获得链表的第index(0-based)个位置的元素
    // 在链表中不是一个常用的操作，练习用
    public E get(int index) {
        if (index < 0 || index > size) {
            throw new IllegalArgumentException("Get failed. Illegal index.");
        }
        Node cur = dummyHead.next;
        for (int i = 0; i < index; i++) {
            cur = cur.next;
        }
        return cur.e;
    }

    // 获得链表的第一个元素
    public E getFirst() {
        return get(0);
    }

    // 获取链表的最后一个元素
    public E getLast() {
        return get(size - 1);
    }

    public void set(int index, E e) {
        if (index < 0 || index > size) {
            throw new IllegalArgumentException("Set failed. Illegal index.");
        }

        Node cur = dummyHead.next;
        for (int i = 0; i < index; i++) {
            cur = cur.next;
        }
        cur.e = e;
    }

    public boolean contains(E e) {
        Node cur = dummyHead.next;

        while (cur != null) {
            if (cur.e.equals(e)) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    // 从链表中删除index(0-based)位置的元素，返回删除的元素
    // 在链表中不是一个常用的操作，练习使用: ）
    public E remove(int index) {
        if (index < 0 || index > size) {
            throw new IllegalArgumentException("Remove failed. Illegal index.");
        }
        Node cur = dummyHead;
        for (int i = 0; i < index; i++) {
            cur = cur.next;
        }
        Node retNode = cur.next;
        cur.next = retNode.next;
        retNode.next = null;

        return retNode.e;
    }

    public E removeFirst() {
        return remove(0);
    }

    public E removeLast() {
        return remove(size - 1);
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();

//        Node cur = dummyHead.next;
//        while (cur != null) {
//            res.append(cur + "->");
//            cur = cur.next;
//        }
//        res.append("NULL");
        for (Node cur = dummyHead.next; cur != null; cur = cur.next) {
            res.append(cur + "->");
        }
        res.append("NULL");

        return res.toString();
    }
}