链式队列

同样有两个引用，第一个front引用指向队列第一个元素，rear引用指向最后一个引用

class LinkQueue {
	//节点
    class Entry {
        int data;
        Entry next;

        public Entry() {
            this.data = -1;
            this.next = null;
        }
        public Entry(int val) {
            this.data = val;
            this.next = null;
        }
    }
    Entry front;
    Entry rear;
    int userSize;
    public LinkQueue() {
        this.userSize = 0;
    }
    //是否为空
    public boolean isEmpty() {
        return userSize == 0;
    }
    //  入队
    public void push(int val) {
        Entry cur = new Entry(val);
        if (isEmpty()) {
            front = cur;
            rear = cur;
        } else {
            rear.next = cur;
            rear = rear.next;
        }
        userSize++;
    }
    //出队
    public void pop() {
        if (isEmpty()) {
            throw new UnsupportedOperationException("空空如也");
        } else {
            front = front.next;
            userSize--;
        }
    }
    public void show() {
        Entry cur = front;
        while (cur != null) {
            System.out.print(cur.data + "  ");
            cur = cur.next;
        }
        System.out.println();
    }
}