用策略模式实现购物车，策略模式实现购物车,public class

用策略模式实现购物车，策略模式实现购物车,public class

public class ShoppingCart {  private final List<Item> items;  public ShoppingCart() {    items = new ArrayList<Item>();  }  public void addItem(Item item) {    items.add(item);  }  public double calcTotalCost() {    double total = 0.0;    for (Item item : items) {      total += item.getPrice();    }    return total;  }  public boolean pay(PaymentMethod method) {    double totalCost = calcTotalCost();    return method.pay(totalCost);  }}

我们可以看到上面的pay方法的参数是一个PaymentMethod实例，这就意味着我们可以根据需要切换不同的支付策略。

public interface PaymentMethod {  public boolean pay(double amount);}

这样你就可以定义任意支付方式的PaymentMethod了。

public class Visa implements PaymentMethod {  private final String name;  private final String cardNumber;  private final Date expires;  public Visa(String name, String cardNumber, Date expires) {    super();    this.name = name;    this.cardNumber = cardNumber;    this.expires = expires;  }  @Override  public boolean pay(double amount) {    // Open Comms to Visa    // Verify connection    // Paybill using these details    return true; // if payment goes through  }}

public class MasterCard implements PaymentMethod {  private final String name;  private final String cardNumber;  private final Date expires;  public MasterCard(String name, String cardNumber, Date expires) {    super();    this.name = name;    this.cardNumber = cardNumber;    this.expires = expires;  }  @Override  public boolean pay(double amount) {    // Open Comms to Mastercard    // Verify connection    // Paybill using these details    return true; // if payment goes through  }}