在数组列表中查找hashmap和平均对象时遇到问题

Question

在这个程序中，我想输入假股票并按股票代码搜索它们，并打印最近购买的250只股票的平均成本。这里是我到目前为止的地方，每当我输入2，程序崩溃，没有任何错误消息。

package stocks;
import java.util.*;
public class Stocks {
    private String sym;
    private List<Purchase> purchases;
    public Stocks(final String symbol) {
        this.sym = symbol;
        purchases = new ArrayList<Purchase>();
    }
    public void addPurchase(final int amt, final double cost) {
        purchases.add(new Purchase(amt, cost));
    }
    public String getSym() {
        return sym;
    }
    public void setSym() {
        this.sym = sym;
    }
    public double getAvg250() {
        int i = 0;
        int total = 0;
        int shares = 0;
        while (i < purchases.size()) {
            Purchase p = purchases.get(i);
            if (shares + p.getAmt() >= 250) {
                total += (250 - shares) * p.getCost();
                shares = 250;
                break;
            }
            shares += p.getAmt();
            i++;
        }
        return total * 1.0 / shares;
    }
    public class Purchase {
        private int amt;
        private int cost;
        public Purchase(int amt, double cost) {
        }
        public int getAmt() {
            return amt;
        }
        public void setAmt(int amt) {
            this.amt = amt;
        }
        public int getCost() {
            return cost;
        }
        public void setCost(int cost) {
            this.cost = cost;
        }
    }
    public static void main(String[] args) {
        int choice = 0;
        ArrayList<Stocks> StocksList = new ArrayList<Stocks>();
        Map<String, Stocks> stocks = new HashMap<String, Stocks>();
        while (choice == 0) {
            System.out.println("Enter 1 to input a new stock, or 2 to query a stock's price, 3 to quit: ");
            Scanner sc1 = new Scanner(System.in);
            choice = sc1.nextInt();
            if (choice == 1) {
                Scanner sc2 = new Scanner(System.in);
                System.out.println("Please enter the stock symbol: ");
                String sym = sc2.next();
                System.out.println("Please enter the number of shares: ");
                int amt = sc2.nextInt();
                System.out.println("Please enter the price per share: ");
                double cost = sc2.nextDouble();
                Stocks s = stocks.get(sym);
                if (s == null) {
                    s = new Stocks(sym);
                    stocks.put(sym, s);
                }
                s.addPurchase(amt, cost);
                choice = 0;
                if (choice == 2) {
                    Scanner sc3 = new Scanner(System.in);
                    System.out.println("Please enter the symbol of the stock you wish to see: ");
                    String search = sc3.next();
                    if (stocks.containsKey(search)) {
                        System.out.println(search + "'s LIFO price is " + s.getAvg250());
                        choice = 0;
                    }
                }
                if (choice == 3) {
                }
            }
        }
    }
}

Answer 1

检查用户是否在if块中输入了"2"，以检查用户是否输入了"1"。因为在if (choice == 1)块之后选择仍然是2，你的程序离开while循环。

应该类似于(如果你保持这种编程风格)

while (choice == 0) {
   // ...
   if (choice == 1) {
   } 
   if (choice == 2) {
   }
   if (choice == 3) {
     break;
   }
   // ...
   choice = 0
}

代替

while (choice == 0) {
   // ...
   if (choice == 1) {
      choice = 0;
      // choice 2 will never be true 
      if (choice == 2) {
      }
   }
}