策略.md

策略 Strategy

重点等级：:star::star::star:

定义一个算法组，封装每一个算法，并使其可互换。策略让算法独立于使用它的客户端而独立地变化。

在有多种算法相似的情况下，避免过多if else语句的尴尬。

示例代码

以一个支付场景为例，支付是可以使用 Paypal、信用卡等等，可以使用不同的策略来进行代码设计。

//支付接口
public interface PaymentStrategy {

	public void pay(int amount);
}

//信用卡支付
public class CreditCardStrategy implements PaymentStrategy {

	private String name;
	private String cardNumber;
	private String cvv;
	private String dateOfExpiry;

	public CreditCardStrategy(String nm, String ccNum, String cvv, String expiryDate){
		this.name=nm;
		this.cardNumber=ccNum;
		this.cvv=cvv;
		this.dateOfExpiry=expiryDate;
	}
	@Override
	public void pay(int amount) {
		System.out.println(amount +" paid with credit/debit card");
	}

}

//Paypal 支付
public class PaypalStrategy implements PaymentStrategy {

	private String emailId;
	private String password;

	public PaypalStrategy(String email, String pwd){
		this.emailId=email;
		this.password=pwd;
	}

	@Override
	public void pay(int amount) {
		System.out.println(amount + " paid using Paypal.");
	}

}

//购物车
public class ShoppingCart {

	//List of items
	List<Item> items;

	public ShoppingCart(){
		this.items=new ArrayList<Item>();
	}

	public void addItem(Item item){
		this.items.add(item);
	}

	public void removeItem(Item item){
		this.items.remove(item);
	}

	public int calculateTotal(){
		int sum = 0;
		for(Item item : items){
			sum += item.getPrice();
		}
		return sum;
	}

	public void pay(PaymentStrategy paymentMethod){
		int amount = calculateTotal();
		paymentMethod.pay(amount);
	}
}


public class ShoppingCartTest {

	public static void main(String[] args) {
		ShoppingCart cart = new ShoppingCart();

		Item item1 = new Item("1234",10);
		Item item2 = new Item("5678",40);

		cart.addItem(item1);
		cart.addItem(item2);

		//pay by paypal
		cart.pay(new PaypalStrategy("myemail@example.com", "mypwd"));

		//pay by credit card
		cart.pay(new CreditCardStrategy("Pankaj Kumar", "1234567890123456", "786", "12/15"));

    //50 paid using Paypal.
    //50 paid with credit/debit card
	}

}

枚举避免ifelse

public enum ChannelRuleEnum {

    /**
     * 头条
     */
    TOUTIAO("TOUTIAO",new TouTiaoChannelRule()),
    /**
     * 腾讯
     */
    TENCENT("TENCENT",new TencentChannelRule()),
    ;

    public String name;

    public GeneralChannelRule channel;

    ChannelRuleEnum(String name, GeneralChannelRule channel) {
        this.name = name;
        this.channel = channel;
    }

  //匹配
    public static ChannelRuleEnum match(String name){
        ChannelRuleEnum[] values = ChannelRuleEnum.values();
        for (ChannelRuleEnum value : values) {
            if(value.name.equals(name)){
                return value;
            }
        }
        return null;
    }
    public String getName() {
        return name;
    }

    public GeneralChannelRule getChannel() {
        return channel;
    }
}

public static void main(String[] args) {
    String sign = "TOUTIAO";
    ChannelRuleEnum channelRule = ChannelRuleEnum.match(sign);
    GeneralChannelRule rule = channelRule.channel;
    rule.xxx();
}