队列——Java实现

package struct;
 
interface IQueue{
    //入队列
    void add(Object obj);
    //出队列
    Object remove();
    //队列中元素个数（栈大小）
    int size();
    //判断队列是否为空
     boolean isEmpty();
     //取队头元素
     Object getQueueHead();
     //取队尾元素
     Object getQueueTail();
     //清空队列
     void clear();
}
class Factory3{
    private Factory3(){}
    public static IQueue getIQueueInstance(){
        return new LinkQueueImpl();
    }
}
class LinkQueueImpl implements IQueue{
    Node head;//队列的头
    Node tail;//队列的尾
    int size;
    class Node{
        Node prev;
        Node next;
        Object data;
        public Node(Object data) {
            super();
            this.data = data;
        }
    }
    //入队列(头插)
    public void add(Object obj) {
        Node newNode = new Node(obj);
        //空队列
        if(head == null){
            head = newNode;
            tail = newNode;
            size++;
        }else{
            Node node  = tail;
            newNode.next = node;
            node.prev = newNode;
            tail = newNode;
            size++;
        }
    }
    //出队列（尾删）
    public Object remove() {
        if(isEmpty()){
            return "无要删除元素";
        }else if(head == tail){
            //只有一个元素的队列
            size--;
            return head.data;
        }else{
            Node node = head;
            head = node.prev;
            node.prev = null;
            size--;
            return head.data;
        }
    }
    //求队列长度
    public int size() {
        return size;
    }
    //求队列是否为空
    public boolean isEmpty() {
        return (size()==0);
    }
    //取队首元素
    public Object getQueueHead() {
        return head.data;
    }
    //取对尾元素
    public Object getQueueTail() {
        return tail.data;
    }
    //打印队列
    public void print(){
        myPrint(head);
    }
    //队首到对尾打印元素
    private void myPrint(Node head){
        for(Node node = head;node!=null;node = node.prev){
            System.out.print(node.data+" ");
        }
    }
    //置空队列
    public void clear() {
        if(head == null){
            System.out.println("空队列");
        }else{
            //非空队列
            Node node1 = tail;
            Node node = head;
            for(node = head;head!=tail;){
                head = head.prev;
                node.prev = null;
                node.data = null;
                size--;
            }
            node1.next = null;
            node1.data = null;
            size--;
        }
    }
}
public class LinkQueue {
    public static void main(String[] args) {
        IQueue queue = Factory3.getIQueueInstance();
        //向下转型
        LinkQueueImpl queue1 = (LinkQueueImpl)queue;
        System.out.println("以下为空队列测试情况");
        System.out.println("================remove测试函数==================");
        System.out.println(queue.remove());
        System.out.println("================size测试函数==================");
        System.out.println(queue.size());
        System.out.println("================isEmpty测试函数==================");
        System.out.println(queue.isEmpty());
        System.out.println("以下为非空队列测试情况");
        System.out.println("================add和print测试函数==================");
        queue.add("hello");
        queue.add("world!");
        queue.add("hi");
        queue.add("陕科大!");
        queue.add("today");
        queue.add("is");
        queue.add("4月18号!");
        queue1.print();
        System.out.println();
        System.out.println("================getQueueHead测试函数==================");
        System.out.println(queue.getQueueHead());
        System.out.println("================getQueueTail测试函数==================");
        System.out.println(queue.getQueueTail());
        System.out.println("================remove测试函数==================");
        System.out.println(queue.remove());
        System.out.println(queue.remove());
        System.out.println("================remove后print测试函数==================");
        queue1.print();
        System.out.println();
        System.out.println("================size测试函数==================");
        System.out.println(queue.size());
        System.out.println("================isEmpty测试函数==================");
        System.out.println(queue.isEmpty());
        System.out.println("================clear测试函数==================");
        queue.clear();
        System.out.println(queue.size());
    }
}