策略模式中體現了兩個非常基本的面向對象設計的原則:
1.封裝變化的概念2.編程中使用接口,而不是對接口的實現
策略模式的組成
1.抽象策略角色:策略類,接口或這抽象類
2.具體策略角色:實現或繼承了接口或抽象類的實現類,包裝了相關的算法和行爲
3.環境角色:持有一個策略類的引用,最終給客戶端調用
4.客戶端
策略模式的實現:
環境類負責維持和查詢具體策略類,由於算法和環境獨立開來,算法的修改都不會影響環境和客戶端。
策略模式的編寫步驟:
1.對策略對象定義一個公共接口
2.編寫策略類,實現接口
3.編寫環境類:在使用策略對象的類中保存一個對策略對象的引用
4.在環境類中實現對策略對象的set和get方法,或者使用構造方法完成賦值
5.最後編寫客戶端訪問環境類和策略類
//策略模式的接口
public interface Strategy
{
public int calculate(int a, int b);
}
//加減乘除四個具體策略類
public class AddStrategy implements Strategy
{
public int calculate(int a, int b)
{
return a + b;
}
}
public class SubtractStrategy implements Strategy
{
public int calculate(int a, int b)
{
return a - b;
}
}
public class MultiplyStrategy implements Strategy
{
public int calculate(int a, int b)
{
return a * b;
}
}
public class DivideStrategy implements Strategy
{
public int calculate(int a, int b)
{
return a / b;
}
}
//環境類
public class Environment
{
private Strategy strategy;
public Environment(Strategy strategy)
{
this.strategy = strategy;
}
public Strategy getStrategy()
{
return strategy;
}
public void setStrategy(Strategy strategy)
{
this.strategy = strategy;
}
public int calculate(int a ,int b)
{
return strategy.calculate(a , b);
}
}
//客戶端
public class Client
{
public static void main(String[] args)
{
AddStrategy addStrategy = new AddStrategy();
Environment environment = new Environment(addStrategy);
System.out.println(environment.calculate(3, 4));
SubtractStrategy subtractStrategy = new SubtractStrategy();
environment.setStrategy(subtractStrategy);
System.out.println(environment.calculate(3, 4));
MultiplyStrategy multiplyStrategy = new MultiplyStrategy();
environment.setStrategy(multiplyStrategy);
System.out.println(environment.calculate(3, 4));
DivideStrategy divideStrategy = new DivideStrategy();
environment.setStrategy(divideStrategy);
System.out.println(environment.calculate(3, 4));
}
}