Question

在这个程序中，我想输入虚假股票并用股票代码搜索它们，并打印最后买入的250只股票的平均成本。这是我到目前为止的地方，每当我输入2时，程序崩溃而没有任何错误消息。

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

您检查用户是否输入了＆＃34; 2＆＃34;在if块中检查用户是否输入＆＃34; 1＆＃34;。而且因为if (choice == 1)阻止你的程序离开while循环后选择仍然是2。

应该是这样的（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
}

而不是

while (choice == 0) {
   // ...
   if (choice == 1) {

      choice = 0;

      // choice 2 will never be true 
      if (choice == 2) {
      }

   }
}

无法在arraylist中搜索hashmap和平均对象

1 个答案: