策略模式定义了算法族(也可以说是一组行为)，分别封装起来，让它们之间可以相互交替，此模式让算法的变化独立于使用算法的客户。
示例—不同鸭子的表现
设计几种鸭子的类，比如绿头鸭、红头鸭等。鸭子都由不同的样子，有些会飞，有些不会飞（比如橡皮鸭），有些会叫，有些不会叫（比如橡皮鸭）。
UML图表示
鸭子的策略模式设计
代码演示
- 由于每个鸭子会飞，但有些会飞，有些不会飞，所以设计一个飞行行为接口，用不同实现表示
interface FlyBehavior{
void fly();
}
class FlyWithWings implements FlyBehavior{
@Override
public void fly() {
System.out.println("I'm flying!!");
}
}
class FlyNoWay implements FlyBehavior{
@Override
public void fly() {
System.out.println("I can't fly");
}
}
- 大部分鸭子会叫，也有不会叫的鸭子，而且叫的声音也不同。也采用接口+实现的方式
interface QuackBehavior{
void quack();
}
class Quack implements QuackBehavior{
@Override
public void quack() {
System.out.println("Quack");
}
}
class MuteQuack implements QuackBehavior{
@Override
public void quack() {
System.out.println("<< Silence >>");
}
}
class Squeak implements QuackBehavior{
@Override
public void quack() {
System.out.println("Squeak");
}
}
- 设计鸭子的基类，总结鸭子的行为有：飞、叫、游泳、显示的外观。
public abstract class Duck {
private FlyBehavior flyBehavior;
private QuackBehavior quackBehavior;
public void swim(){
System.out.println("I can swim");
}
public abstract void display();
public void performFly(){
flyBehavior.fly();
}
public void performQuack(){
quackBehavior.quack();
}
public void setFlyBehavior(FlyBehavior flyBehavior){
this.flyBehavior = flyBehavior;
}
public void setQuackBehavior(QuackBehavior quackBehavior){
this.quackBehavior = quackBehavior;
}
}
- 四种鸭子的实现：绿头鸭、红头鸭、橡皮鸭、诱饵鸭。
class MallardDuck extends Duck{
MallardDuck(){
setFlyBehavior(new FlyWithWings());
setQuackBehavior(new Quack());
}
@Override
public void display() {
System.out.println("I'm a green head duck");
}
}
class RedHeadDuck extends Duck{
RedHeadDuck(){
setFlyBehavior(new FlyWithWings());
setQuackBehavior(new Quack());
}
@Override
public void display() {
System.out.println("I'm a red head duck");
}
}
class RubberDuck extends Duck{
RubberDuck(){
setFlyBehavior(new FlyNoWay());
setQuackBehavior(new MuteQuack());
}
@Override
public void display() {
System.out.println("I'm a model duck");
}
}
class DecoyDuck extends Duck{
DecoyDuck(){
setFlyBehavior(new FlyNoWay());
setQuackBehavior(new Squeak());
}
@Override
public void display() {
System.out.println("I'm a decoy duck");
}
}
- 添加测试代码
public static void main(String[] args) {
MallardDuck mallardDuck = new MallardDuck();
mallardDuck.swim();
mallardDuck.display();
mallardDuck.performFly();
mallardDuck.performQuack();
System.out.println("~~~~~~~~~~~~~~~~~~~");
RedHeadDuck redHeadDuck = new RedHeadDuck();
redHeadDuck.swim();
redHeadDuck.display();
redHeadDuck.performFly();
redHeadDuck.performQuack();
System.out.println("~~~~~~~~~~~~~~~~~~~");
RubberDuck rubberDuck = new RubberDuck();
rubberDuck.swim();
rubberDuck.display();
rubberDuck.performFly();
rubberDuck.performQuack();
System.out.println("~~~~~~~~~~~~~~~~~~~");
DecoyDuck decoyDuck = new DecoyDuck();
decoyDuck.swim();
decoyDuck.display();
decoyDuck.performFly();
decoyDuck.performQuack();
}
- 测试结果
I can swim
I'm a green head duck
I'm flying!!
Quack
~~~~~~~~~~~~~~~~~~~
I can swim
I'm a red head duck
I'm flying!!
Quack
~~~~~~~~~~~~~~~~~~~
I can swim
I'm a model duck
I can't fly
<< Silence >>
~~~~~~~~~~~~~~~~~~~
I can swim
I'm a decoy duck
I can't fly
Squeak
