java - 输入数组列表时遇到问题，尝试了一切

Question

我正在尝试将数据输入到包含股票对象的股票数组列表中。股票由代码、股票数量和每股成本组成。这是我的代码，我已经被困了几个小时，无法弄清楚为什么我的输入没有进入数组列表。这是我的代码:

import java.util.*;
import java.util.Scanner;

public class stock {

 String sym;
 int amt;
 double cost;

 public stock(String sym, int amt, double cost){
  sym = this.sym;
  amt = this.amt;
  cost = this.cost;
 }

 public String getSym() {
  return sym;
 }


 public int getAmt() {
  return amt;
 }


 public double getCost() {
  return cost;
 }

    @Override
    public String toString() {
         return ("sym: "+this.getSym()+
                     " amt : "+ this.getAmt() +
                     " cost: "+ this.getCost());
    }


public static void main(String[] args) {

 int choice = 0;
 ArrayList<stock> Stocks = new ArrayList<stock>();

 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();

   stock list = new stock(sym, amt, cost);

   Stocks.add(list);

   System.out.println(Stocks.toString());

}
}
}

这是我的输出:

[sym: null amt : 0 cost: 0.0]

Answer 1

您的字段分配是从右到左

sym = this.sym;

应该是

this.sym = sym;

其他Stock字段也是如此