数据结构-链表(二、底层实现---源码)

package LinkedList;


public class LinkedList<E> {
    //内部类
    private class Node {
        public E e;
        public Node next;

        //      用户传来e 和 next
        public Node(E e, Node next) {
            this.e = e;
            this.next = next;
        }

        //      用户传来只传来e
        public Node(E e) {
            this(e, null);
        }

        //      用户没有传任何参数
        public Node() {
            this(null, null);
        }


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

    //虚拟头结点
    private Node dummyhead;
    //记录链表中有多少个元素
    private int size;


    //对于一个空的链表来说 他是存在一个空的节点的，这个节点就是唯一的虚拟头结点
    public LinkedList() {
        dummyhead = new Node(null, null);
        size = 0;
    }

    //获取当前链表中元素的个数
    public int getSize() {
        return size;
    }

    //返回链表是否为空
    public boolean isEmpty() {
        return size == 0;
    }


    //在链表的index(0-based)位置添加新的元素e
    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一直向前移动  直到移动到index-1的位置
            prev = prev.next;
        }
        //新插入的node    prev.next = new Node(e, prev.next);  与下面三句话等价
        Node node = new Node(e);
        node.next = prev.next;
        prev.next = node;
        size++;
    }

    //在链表的头插入新的元素
    public void addFirst(E e) {
        add(0, e);
    }

    //在链表的尾插入新的元素
    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
    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;
    }

    //获取列表的第一个元素
    public E getFirst() {
        return get(0);
    }

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

    // 修改链表的第index(0-based)个位置的元素为e
    // 在链表中不是一个常用的操作
    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;
    }

    // 查找链表中是否有元素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e
    public E remove(int index) {

        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Remove failed. Illegal index");
        }
        Node prev = dummyhead;
        for (int i = 0; i < index; i++) {
            prev = prev.next;
        }
        Node retNode = prev.next;
        prev.next = retNode.next;
        retNode.next= null;
        size--;
        return retNode.e;
    }

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

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

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

        Node cur = dummyhead.next;
        while (cur != null) {
            res.append(cur + "->");
            cur = cur.next;
        }

//        与上面等价
//        for (Node cur = dummyhead.next; cur != null; cur = cur.next) {
//            res.append(cur + "->");
//        }
        res.append("NULL");
        return res.toString();
    }

    public static void main(String[] args) {
        LinkedList<Integer> linkedList = new LinkedList<Integer>();
        for (int i = 0; i < 5; i++) {
            linkedList.addFirst(i);
            System.out.println(linkedList);
        }
        linkedList.add(2,666);
        System.out.println(linkedList);

        linkedList.remove(2);
        System.out.println(linkedList);


        linkedList.removeFirst();
        System.out.println(linkedList);


        linkedList.removeLast();
        System.out.println(linkedList);
    }
}

测试结果：