java - map 中的增量值(JAVA)

Question

我对这项家庭作业有疑问。我可以处理语法，但不能处理逻辑。你能给我一些提示吗？

我想要实现的是 add 方法将通过使用 increaseAmount 方法来增加产品的数量。现在，每次我调用该方法时，它都会将 amount 的值重置为“1”。使这变得复杂的是我不允许使用任何其他已经使用过的私有(private)变量。

private Map<String, Purchase> shoppingCart = new HashMap<String, Purchase>();

public void add (String product, int price) {
        Purchase purchase = new Purchase (product, 1, price); 
                  //the line abowe returns the value back to 1 which I don't want.

        if(shoppingCart.containsKey(product)) {

            shoppingCart.put(product, purchase);
                purchase.increaseAmount();

        }
        else {
             shoppingCart.put(product, purchase);

产品构造函数:

public Ostos(String product, int amount, int price) {

increaseAmount 方法的代码:

private int amount;

public void increaseAmount() {
    this.amount = (this.amount + 1);

Answer 1

不要在开始时创建新的购买，只有在它不存在时才创建

public void add (String product, int price) {

        if(shoppingCart.containsKey(product)) {
            Purchase purchase = shoppingCart.get(product);
            purchase.increaseAmount();
            //You might have to put the purchase back into the cart I'm not sure
        }
        else {
             Purchase purchase = new Purchase (product, 1, price);
             shoppingCart.put(product, purchase);
        }