package queue;/** * @Title: LinkedListQueue * @ProjectName demo */public class LinkedListQueue
     
       implements Queue
      
        {    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();    }}