java - 创建无限数量的项目

Question

我的代码有什么问题吗？具体来说，对象项 item2[count] 的数组最初我试图将 item1 插入队列中，但遇到了一个问题，即对象 Item 的先前值存储在队列中被新插入的内容覆盖。我的解决方案是声明一个对象数组 item2[count] 并递增 int count ，现在我收到了 insertFront Exception 的异常在线程“main”中 java.lang.ArrayIndexOutOfBoundsException: 0 和 insertRear 线程“main”中的异常 java.lang.ArrayIndexOutOfBoundsException: 0

主要:

public class MyDequeApp {

    public static void main(String[] args) {
        //variables
        String userinNum;
        double userinPrice;
        int queOp=0;

        //???
        int count=0;

        //creating new Item
        Item item1 = new Item();
        //array of items!!!????
        Item[] item2=new Item[count];

        //creating new Scanner      
        Scanner scan1=new Scanner(System.in);

        //user input number of elements in the deque
        System.out.println("Enter the number of elements in the que");
        int queElm=scan1.nextInt();     
        MyDeque theQueue=new MyDeque(queElm);
        //MyDeque theStack=new MyDeque(queElm);

        //do/while so while user selects 1-7 they stay in the switch/case
        do {
            //switch/case menu
            System.out.println("1. Insert to front");
            System.out.println("2. Insert to rear");
            System.out.println("3. Remove from front");
            System.out.println("4. Remove from rear");
            System.out.println("5. Peek front");
            System.out.println("6. Peek rear");
            System.out.println("7. Display deque");
            System.out.println("Anything else to Quit");

            //user input the case number
            queOp=scan1.nextInt();
            scan1.nextLine();

            //for(int i=0; i<100; i++) {  //for start
                switch(queOp) {     
                    //insert to front
                    case 1:
                        System.out.println("Enter an item number");
                        userinNum=scan1.nextLine();
                        item1.setNum(userinNum);
                        System.out.println("Enter a price");
                        userinPrice=scan1.nextDouble();
                        scan1.nextLine();
                        item1.setPrice(userinPrice);
                        System.out.println(item1.toString());
                        item2[count]=item1;
                        theQueue.insertFront(item2[count]);
                        count++;
                        break;                  
                    //insert to rear
                    case 2:
                        System.out.println("Enter an item numbeR");
                        userinNum=scan1.nextLine();
                        item1.setNum(userinNum);
                        System.out.println("Enter a pricE");
                        userinPrice=scan1.nextDouble();
                        scan1.nextLine();
                        item1.setPrice(userinPrice);
                        System.out.println(item1.toString());
                        //item2[count]=item1;
                        theQueue.insertRear(item2[count]);
                        count++;
                        break;
                }
          //}
        }
    }
}

类MyDeque中的方法

public class MyDeque {

    private int maxSize;
    private Item[] queArray;
    private int front;
    private int rear;
    private int nItems;

    //constructor
    public MyDeque(int s) {
        maxSize = s;
        queArray = new Item[maxSize];
        front = 0;
        rear = -1;
        nItems = 0;
    }

    //insertFront()
    //For an insertion operation, you have to prompt the user to type in the item#
    //and the price. Create an object of the Item and then pass the object as the
    //argument to the insertion method
    public void insertFront(Item x) {
        if(front==maxSize)
        front=0;
        queArray[front++]=x;
        nItems++;
    }

    //insertRear()
    public void insertRear(Item y) {
        if(rear==maxSize-1) //wraparound
            rear=-1;
        queArray[++rear]=y; //CHANGED TO ++rear increment rear and insert
        nItems++;   //one more item
    }
}

Answer 1

你的问题很简单。

当您循环获取用户输入以将另一个 Item 插入队列或数组时，您需要创建一个新的 Item 对象:

Item newItem = new Item();

如果您不创建新项目，那么您只是更改队列中现有项目的值，从而有效地覆盖它们的值。

您也不需要该数组。

根据我们可能的输入，逻辑应类似于:queueOp 是一个 int，因此您应该调用 scan1.nextInt()

Get queueOp from user
switch(queueOp)
 case 1:
    create new Item and set values (`new Item()`)
    call method insertFront(pass new Item)
 case 2: 
    create new Item and set values
    call method insertRear(pass new Item)