java - 读取Orders并填充ArrayList

Question

我正在尝试读取这样的数据文件:

N 1000.0 NY              R 2000.0 CA 0.09            R 500.0 GA 0.07           N 2000.0 WY             O 3000.0 Japan 0.11 20.0            N 555.50 CA            O 3300.0 Ecuador 0.03 30.0          R 600.0 NC 0.06 

and use it to fill an arrayList

My program consists of a abstract class and three classes to implement it:

1. NonProfitOrder

public class NonProfitOrder extends Order {

public NonProfitOrder(double price, String location) {
    super(price, location);
}
public double calculateBill() {
    return getPrice();
}
public String printOrder(String format){
    String Long = "Non-Profit Order" + "\nLocation: " + getLocation() +  "\nTotal Price: " + getPrice();
    String Short = "Non-Profit Order-Location: " + getLocation() + ", " + "Total Price: " + getPrice();
    if (format.equals("Long")){
        return Long;
    }
    else{
        return Short;
    }
}
}

2。常规订单

public class RegularOrder extends Order {
double taxRate;

public RegularOrder(double price, String location, double taxRate) {
    super(price, location);
    this.taxRate = taxRate;
}
private double calcTax() {
    double tax;
    tax = getPrice() * taxRate;
    return tax;
}
public double calculateBill() {
    double bill;
    bill = price + calcTax();
    return bill;
}
public String printOrder(String format){
    String Long = "Regular Order" + "\nLocation: " + getLocation() +  "\nPrice: " + getPrice() + 
            "\nTax: " + calcTax() + "\nTotal Price: " + calculateBill();
    String Short = "Regular Order-Location: " + getLocation() + ", " + "Total Price: " + calculateBill();
    if (format.equals("Long")){
        return Long;
    }
    else{
        return Short;
    }
}
}

另一个与 RegularOrder 非常相似

我的问题主要出在我的身上。我必须使用一个方法 readOrders(fileName:string):ArrayList<Order>

public static ArrayList<Order> readOrders (String fileName) throws FileNotFoundException{
    String type;
    Scanner s = new Scanner(new File("orders.txt"));
    ArrayList<Order> orders = new ArrayList<Order>();
    while (s.hasNext()){
        type = s.nextLine();
    }
    switch(type) {
        case 1: type = NonProfitOrder();
            break;
        case 2: type = RegularOrder();
            break;
        case 3: type = OverseasOrder();
    return orders;
}

}

我不知道如何正确执行此操作，因为它仍然显示

readOrders can't be resolved to a type.

以及第一个 readOrders 的其他问题.

我用某种开关状态更新了我的代码，但这不起作用。我应该使用 N、O、R 而不是情况 1、2、3，或者我将如何引用每种类型的订单？另外，我遇​​到了“类型不匹配”错误，但我无法修复它。

Answer 1

您没有正确初始化 ArrayList 和读取订单方法。这里的代码不正确，该方法在 ; 之后结束，并且不执行任何操作，其余部分无效

ArrayList<Order> readOrders (String fileName); {
    ArrayList<Order> orders2 = new readOrders("orders.txt");
}

您需要做的是创建一个方法readOrder，如下所示See this post on how to read in the file 。除了您的情况之外，您需要在循环中做更多工作来创建 Order 对象

public static ArrayList<Order> readOrders (String fileName){
     ArrayList<Order> orders = new ArrayList<Order>();
     //Read in lines from your file
     //Decide which type of order it is and create it
     //Add it to the list
     //Repeat until end of file
     return orders
}

然后在你的主要方法中

public static void main(String[] args) {
     ArrayList<Order> loadedOrders = readOrders("orders.txt");
     //... rest of your code
}

额外编辑

要将它们插入列表中，请执行以下操作

char firstChar =  //Read in the first character of the line from the file
Order anOrder;
switch(firstChar)
{
    case 'N':
       anOrder = new NonProfitOrder();  //adding arguments to construtor as needed
       break;
    case 'R':
       anOrder = new RegularOrder();
       break;
    default:
       anOrder = new Order();
       break;
 }
 loadedOrders.add(anOrder);

然后在阅读时，根据您需要对顺序执行的操作，您可能需要使用 instanceof 和强制转换。但是，如果在基类中声明了方法并且仅在子类中重写它们，则可以避免这种情况，然后当您从列表中读取时，首先在子类中查找该方法，如果找不到，则查找在基类中，那么如果它不在基类中显然你会得到一个错误。拥有抽象基类非常有用，这意味着您可以避免这样做

Order ord = orders.get(anIndex)

if(ord instanceof NonProfitOrder)
    ((NonProfitOrder)ord).aNonprofitOrderSpecificMethod()
else if (ord instanceof RegularOrder())
    ((RegularOrder)ord).aRegularOrderSpecificMethod();
//.....