Strategy Pattern

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

We encapsulate Duck Behavior out of Duck class.

Abstractions

package headfirst.strategy;

public abstract class Duck {
	FlyBehavior flyBehavior;
	QuackBehavior quackBehavior;
 
	public Duck() {
	}
 
	public void setFlyBehavior (FlyBehavior fb) {
		flyBehavior = fb;
	}
 
	public void setQuackBehavior(QuackBehavior qb) {
		quackBehavior = qb;
	}
 
	abstract void display();
 
	public void performFly() {
		flyBehavior.fly();
	}
 
	public void performQuack() {
		quackBehavior.quack();
	}
 
	public void swim() {
		System.out.println("All ducks float, even decoys!");
	}
}

package headfirst.strategy;

public interface FlyBehavior {
	public void fly();
}

Implementations

package headfirst.strategy;

public class FlyWithWings implements FlyBehavior {
	public void fly() {
		System.out.println("I'm flying!!");
	}
}

public class FlyRocketPowered implements FlyBehavior {
	public void fly() {
		System.out.println("I'm flying with a rocket");
	}
}

package headfirst.strategy;

public class MallardDuck extends Duck {
 
	public MallardDuck() {
 
		quackBehavior = new Quack();
                flyBehavior = new FlyWithWings();
 

	}
 
	public void display() {
		System.out.println("I'm a real Mallard duck");
	}
}

public class ModelDuck extends Duck {
	public ModelDuck() {
		flyBehavior = new FlyNoWay();
		quackBehavior = new Quack();
	}

	public void display() {
		System.out.println("I'm a model duck");
	}
}

public class MiniDuckSimulator1 {
 
	public static void main(String[] args) {
 
		Duck mallard = new MallardDuck();
		mallard.performQuack();
		mallard.performFly();
   
		Duck model = new ModelDuck();
		model.performFly();
		model.setFlyBehavior(new FlyRocketPowered()); // setting behavior dynamically
		model.performFly();

	}
}