java - Front 和 Rear 元素只显示当前添加的元素，而不是第一个添加的元素和最后一个添加的元素

Question

我在大学学习 DSA 概念时遇到了一些困难，我正在尝试自己学习。作为我尝试的一部分，我正在创建一个简单的应用程序，系统应在其中接受用户的预订并将它们插入队列。

我为此使用了 JAVA，但问题是输出始终只显示在该代码运行时添加的元素，而不是之前添加的元素，

例子：

我添加了名为 John 和 Steve 的 2 个元素，然后又进行了一轮并添加了一个名为 Peter 的人，根据 FIFO 概念，前面的索引值应该是 Peter，而后面的值应该是 John，因为首先添加了 John。

但是我的代码仅将 Peter 显示为第一和后索引值。

代码块如下。

节点类代码

public class Nodes {
    
    public int BanquetHall_ID;
    public int Reservation_ID;
    public String Customer_Name;
    public int Contact_No;
    public String Reservation_Date;
    public int Menu_Selection;
    public String Customer_Email_Address;
    Nodes next ;
    int data;

    
    public Nodes(int BanquetHall_ID, int Reservation_ID, String Customer_Name, 
            int Contact_No,String Customer_Email_Address ,String Reservation_Date, int Menu_Selection)
    {
        this.BanquetHall_ID=BanquetHall_ID;
        this.Reservation_ID=Reservation_ID;
        this.Customer_Name=Customer_Name;
        this.Contact_No=Contact_No;
        this.Customer_Email_Address=Customer_Email_Address;
        this.Reservation_Date=Reservation_Date;
        this.Menu_Selection=Menu_Selection;
        this.next=null;
    }
}

队列类代码

public class Queue {

Nodes front, rear;

public Queue()
{
    this.front = this.rear = null;
}      
        
    void enQueue(int BanquetHall_ID, int Reservation_ID, String Customer_Name, int Contact_No, 
            String Customer_Email_Address,String Reservation_Date, int Menu_Selection)
    {
        Nodes temp = new Nodes(BanquetHall_ID , Reservation_ID , Customer_Name , Contact_No , 
                Customer_Email_Address , Reservation_Date , Menu_Selection);
            
            if(this.rear == null)
            {                   
                this.front = this.rear = temp;
                return;  
            }
            
            this.rear.next = temp;
            this.rear = temp;
    }

    public void deQueue(int Reservation_ID)
    {
        if (this.front == null)
        {
            return;
        }

        Nodes temp = this.front;
        this.front= this.front.next;
            
        if (this.front == null)
        {
            this.rear=null;
        }
    }

主类代码

    else if(c==2)
    {
          int crun = 1;
            while(crun!=0)
            {
            System.out.println("***** You Have Selected To Make A Reservation *****");
            System.out.println("----- Please Provide The Accurate Details Below -----");
            
            System.out.println("Enter preferred Hall ID : ");
            int id = sc.nextInt();
            
            System.out.println("Enter preferred Reservation ID (Provide An ID In Numbers Which You Can Always Remember) : ");
            int rid=sc.nextInt();
            
            sc.nextLine();
            
            System.out.println("Enter Your Name : ");
            String name = sc.nextLine();
            
            System.out.println("Enter Your Contact Number : ");
            int contact = sc.nextInt();
            
            sc.nextLine();
            
            System.out.println("Enter Your Email Address : ");
            String email = sc.nextLine();
            
            System.out.println("Enter Your Reservation Date (YYYY-MM-DD): ");
            String date = sc.nextLine();
            
            System.out.println("Enter Your Menu Selection : ");
            int menu = sc.nextInt();
            
            Queue nd = new Queue();
            nd.enQueue(id, rid, name, contact, email, date, menu);
            System.out.println("Inserted Element Index : "+ nd.front.Customer_Name);
            System.out.println("Last element Index : "+nd.rear.Customer_Name);
            
            Scanner cs = new Scanner(System.in);
            
            System.out.println("Would you like to rerun this program? 1= Yes, 0 = No");
            crun = cs.nextInt();
            }
    }

标签： javaarraysqueuenodesdsa