数据结构学习（五） Java链表实现队列

package queue;

/**
 * @Title: LinkedListQueue
 * @ProjectName demo
 */
public class LinkedListQueue<E> implements Queue<E> {

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

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

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

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

    private int size;
    private Node head, tail;

    public LinkedListQueue() {
        size = 0;
        head = null;
        tail = null;
    }

    @Override
    public int getSize() {
        return size;
    }

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

    @Override
    public void enqueue(E e) {
        if (tail == null) {
            tail = new Node(e);
            head = tail;
        }else{
            tail.next = new Node(e);
            tail = tail.next;
        }
        size ++;
    }

    @Override
    public E dequeue() {
        if (isEmpty()){
            throw new IllegalArgumentException("dequeue error..");
        }
        Node cur = head;
        head = head.next;
        cur.next = null;
        if (head == null){
            tail = null;
        }
        size--;
        return cur.e;
    }

    @Override
    public E getFront() {
        if (isEmpty()){
            throw new IllegalArgumentException("GetFront error..");
        }
        return head.e;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("front:");
        Node h = head;
        while (h != null) {
            sb.append("--->"+h.e);
            h = h.next;
        }
        sb.append("tail");
        return sb.toString();
    }
}