创建了一个具有股票持有情况功能的 Stock 类和 Dividend Stock 类作为一个简化的实现去掉了对参数的有效性验证等细节

    public class Stock {
    private String symbol;
    private int totalShares;
    private double totalCost;
    
    // Initializes a new Stock with no shares purchased.
    public Stock(String theSymbol) {
    symbol = theSymbol;
    totalShares = 0;
    totalCost = 0.0;
     }
    
    // Returns the total shares purchased of this stock.
    public int getTotalShares() {  return totalShares; }
    // Returns the total profit or loss earned on this stock.
    public double getProfit(double currentPrice) {
    double marketValue = totalShares * currentPrice;
    return  marketValue - to