策略模式
策略模式(Strategy Pattern):定义一系列算法类,将每一个算法封装起来,并让它们可以相互替换,此模式让算法的变化不会影响到使用算法的用户。 如果代码中有很多的if..else.. 就可以使用策略模式来解决这些问题。
适用场景
系统有很多类,而他们的区别仅仅在于他们的行为不同
一个系统需要动态地在几种算法中选择一种
优点
对开闭原则完美地支持
避免使用多重条件转移语句
提高算法地保密性和安全性
缺点
客户端必须知道所有的策略类,并自行决定使用哪一个策略类
产生很多的策略类
下面我们引入一种业务场景,超市在店庆的时候,会进行促销,但是促销的策略有多种,满减,立减,返现等不同的方式。
Golang Demo
package strategy
import "fmt"
type Strategy interface {
doPromotion()
}
type Activity struct {
strategy Strategy
}
func NewActivity(strategy Strategy) *Activity {
return &Activity{strategy: strategy}
}
func (a Activity) executeStrategy() {
a.strategy.doPromotion()
}
type FanXianStratege struct {
}
func NewFanXianStratege() *FanXianStratege {
return &FanXianStratege{}
}
func (FanXianStratege) doPromotion() {
fmt.Println("返现促销")
}
type LiJianStrategy struct {
}
func NewLiJianStrategy() *LiJianStrategy {
return &LiJianStrategy{}
}
func (LiJianStrategy) doPromotion() {
fmt.Println("立减促销")
}
type ManJianStrategy struct {
}
func NewManJianStrategy() *ManJianStrategy {
return &ManJianStrategy{}
}
func (ManJianStrategy) doPromotion() {
fmt.Println("满减促销")
}
package strategy
import "testing"
func Test(t *testing.T) {
activity618 := NewActivity(NewFanXianStratege())
activity1111 := NewActivity(NewLiJianStrategy())
activity618.executeStrategy()
activity1111.executeStrategy()
}
Java Demo
package tech.selinux.design.pattern.behavioral.strategy;
public interface Strategy {
void doPromotion();
}
package tech.selinux.design.pattern.behavioral.strategy;
public class Activity {
private Strategy strategy;
public Activity(Strategy strategy) {
this.strategy = strategy;
}
public void executeStrategy() {
strategy.doPromotion();
}
}
package tech.selinux.design.pattern.behavioral.strategy;
public class FanXianStrategy implements Strategy {
@Override
public void doPromotion() {
System.out.println("返现促销");
}
}
package tech.selinux.design.pattern.behavioral.strategy;
public class LiJianStrategy implements Strategy {
@Override
public void doPromotion() {
System.out.println("立减促销");
}
}
package tech.selinux.design.pattern.behavioral.strategy;
public class ManJianStrategy implements Strategy {
@Override
public void doPromotion() {
System.out.println("满减促销");
}
}
package tech.selinux.design.pattern.behavioral.strategy;
public class Test {
public static void main(String[] args) {
Activity activity618 = new Activity(new LiJianStrategy());
Activity activity1111 = new Activity(new FanXianStrategy());
activity618.executeStrategy();
activity1111.executeStrategy();
}
}
上面的案例中就是策略模式的最简单的应用。但是这并不能满足我们复杂的开发。例如,如果我们在Test类中有这样一段代码的话。
package tech.selinux.design.pattern.behavioral.strategy;
import org.apache.commons.lang3.StringUtils;
public class Test {
public static void main(String[] args) {
// Activity activity618 = new Activity(new LiJianStrategy());
// Activity activity1111 = new Activity(new FanXianStrategy());
//
// activity618.executeStrategy();
// activity1111.executeStrategy();
final String strategy = "LIJIAN";
if (StringUtils.equals(strategy, "LIJIAN")) {
Activity activity = new Activity(new LiJianStrategy());
activity.executeStrategy();
} else if (StringUtils.equals(strategy, "MANJIAN")) {
Activity activity = new Activity(new ManJianStrategy());
activity.executeStrategy();
}
}
}
这样话,我们还是避免不了大量的if..else..的使用。此时,我们就可以结合工厂模式,或者享元模式来进行进一步的优化
UML

补充另一个版本的Java/Scala Demo 以及源码解析
Java Demo_
Scala Demo
UML_
源码解析
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