sun公司官方购物车类

ShoppingCart 类

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import java.util.*;

public class ShoppingCart {
    HashMap items = null;
int numberOfItems = 0;

public ShoppingCart() {
      items = new HashMap();
}

public synchronized void add(String mid, Merchandise m) {
    if(items.containsKey(mid)) {
        ShoppingCartItem scitem = (ShoppingCartItem) items.get(mid);
        scitem.incrementQuantity();
    } else {
        ShoppingCartItem newItem = new ShoppingCartItem(m);
        items.put(mid, newItem);
    }

    numberOfItems++;
}

public synchronized void remove(String bookId) {
    if(items.containsKey(bookId)) {
        ShoppingCartItem scitem = (ShoppingCartItem) items.get(bookId);
        scitem.decrementQuantity();

        if(scitem.getQuantity() <= 0)
            items.remove(bookId);

        numberOfItems--;
    }
}

public synchronized Collection getItems() {
      return items.values();
}

protected void finalize() throws Throwable {
      items.clear();
}

public synchronized int getNumberOfItems() {
      return numberOfItems;
}
public synchronized double getTotal() {
    double amount = 0.0;

    for(Iterator i = getItems().iterator(); i.hasNext(); ) {
        ShoppingCartItem item = (ShoppingCartItem) i.next();
        Merchandise merch = (Merchandise) item.getItem();

        amount += item.getQuantity() * merch.getPrice();
    }
    return roundOff(amount);
}

private double roundOff(double x) {
      long val = Math.round(x*100); // cents
      return val/100.0;
}

public synchronized void clear() {
      items.clear();
      numberOfItems = 0;
}

}

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ShoppingCartItem 类

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public class ShoppingCartItem {
    Object item;
    int quantity;

    public ShoppingCartItem(Object anItem) {
        item = anItem;
        quantity = 1;
    }

    public void incrementQuantity() {
        quantity++;
    }

    public void decrementQuantity() {
        quantity--;
    }

    public Object getItem() {
        return item;
    }

    public int getQuantity() {
        return quantity;
    }

}