面试总结之 oop desing 之 The 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.

 

1.Duck 问题(head frist oop)

 

有的能飞，有的能叫，经典问题.

//Duck.java

public abstract class Duck {
FlyBehavior flyBehavior;
QuackBehavior quackBehavior;
public Duck() {
}
public abstract void display();
public void performFly() {
flyBehavior.fly();
}
public void performQuack() {
quackBehavior.quack();
}
public void swim() {
System.out.println(“All ducks float, even decoys!”);
}
}

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”);
}
}

//Type and compile the FlyBehavior interface (FlyBehavior.java) and
//the two behavior implementation classes (FlyWithWings.java and
//FlyNoWay.java).
接口作为一个行为，因为有的能飞有的不能飞，所以不能够在父类里写fly(). 用一个interface作为一个行为汇总，interface下还有其他的行为.

public interface FlyBehavior {
public void fly();
}

---

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

---

public class FlyNoWay implements FlyBehavior {
public void fly() {
System.out.println(“I can’t fly”);
}
}

 

public interface QuackBehavior {
public void quack();
}

---

public class Quack implements QuackBehavior {
public void quack() {
System.out.println(“Quack”);
}
}

---

public class MuteQuack implements QuackBehavior {
public void quack() {
System.out.println(“<< Silence >>”);
}
}

---

public class Squeak implements QuackBehavior {

public void quack() {

System.out.println(“Squeak”);
}
}

Setting behavior dynamically

//Add two new methods to the Duck class:

public void setFlyBehavior(FlyBehavior fb) {
fl yBehavior = fb;
}
public void setQuackBehavior(QuackBehavior qb) {
quackBehavior = qb;
}

//Make a new Duck type (ModelDuck.java).

public class ModelDuck extends Duck {
public ModelDuck() {
flyBehavior = new FlyNoWay();
quackBehavior = new Quack();
}
public void display() {
System.out.println(“I’m a model duck”);
}
}

//Make a new FlyBehavior type (FlyRocketPowered.java).

public class FlyRocketPowered implements FlyBehavior {
public void fly() {
System.out.println(“I’m fl ying with a rocket!”);
}
}

//Change the test class (MiniDuckSimulator.java), add the
//ModelDuck, and make the ModelDuck rocket-enabled.

public class MiniDuckSimulator {
public static void main(String[] args) {
Duck mallard = new MallardDuck();
mallard.performQuack();
mallard.performFly();
Duck model = new ModelDuck();
model.performFly();
model.setFlyBehavior(new FlyRocketPowered());
model.performFly();
}
}

 

转载于:https://www.cnblogs.com/leetcode/p/3208307.html