增加地图中的值（JAVA）

Question

我的家庭工作任务有问题。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方法会通过使用increaseAmount方法增加产品数量。现在，每次调用方法时，它都会将amount的值重置为“1”。使这种复杂化的原因是我不允许使用任何其他私有变量。

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，只有在它尚未存在的情况下创建它

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);
        }

Answer 2

您必须从shoppingCart检索值，然后增加金额。您永远不会致电shoppingCart.get，因此您每次都会盲目地put将新的购买对象添加到地图中来替换该值。