Strategy Pattern(策略模式)

• Definition

The Strategy Pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

• Class Diagram

• Strategy Role

public interface Strategy {
    public void doSomething();
}

• ConcreteStrategy Role

public class ConcreteStrategy1 implements Strategy {
    public void doSomething(){
        System.out.println(“ConcreteStrategy1’s algorithm”);
    }
}

public class ConcreteStrategy2 implements Strategy {
    public void doSomething(){
        System.out.println(“ConcreteStrategy2’s algorithm”);
    }
}

• Context Role

public class Context {
    private Strategy _strategy;
    
    public Context(Strategy strategy){
        this._strategy= strategy;
    }

    public performDoSomething(){
        this._strategy.doSomething();
    }
}

• Client Role

public class Client {
    Strategy strategy = new ConcreteStrategy1();
    Context context = new Context(strategy);
    context.performDoSomething();
}