设计模式15---桥接模式
当一个事物或者过程有很多变化时，比如开车走路，如何我们用继承的方法，类的数目会几何增长。
但是我们如何把每个变化隔离开来，也就是，车子和路况隔离开来，这样每个变化都是独立的。
public abstract class Automobile { public static final int TYPE_CAR = 1; public static final int TYPE_MOTORCYCLE = 2; public abstract int Run(); }
对于路来说，它影响的是不同的比率。
package com.jayfulmath.designpattern.bridge; public abstract class Road { public static final int TYPE_CITY = 1; public static final int TYPE_HIGHWAY = 2; public static final int TYPE_SUBURBAN = 3; protected String TAGNAME; protected Automobile _mAuto; protected double _miles; public abstract double SpeedRate();//汽车速度比率 public Road(double _miles) { this._miles = _miles; } /** * @param _mAuto the _mAuto to set */ public void set_mAuto(Automobile _mAuto) { this._mAuto = _mAuto; } public double Run() { // System.out.println("distance of "+TAGNAME+" is "+_miles+" km"); System.out.println(String.format("distance of %s is %.0f km", TAGNAME,_miles)); double speed = _mAuto.Run()*SpeedRate(); double h = _miles/speed; System.out.println(String.format("%s spend time %.2f hours", TAGNAME,h)); return h; } }
car:
package com.jayfulmath.designpattern.bridge; public class Car extends Automobile { private static Car _mInstance = null; private Car() { super(); } public static Car getInstance() { if(_mInstance == null) { _mInstance = new Car(); } return _mInstance; } @Override public int Run() { // TODO Auto-generated method stub System.out.print("Car Run 50km/h at:"); return 50; } }
Motorcycle:
package com.jayfulmath.designpattern.bridge; public class Motorcycle extends Automobile { private static Motorcycle _mInstance = null; private Motorcycle() { super(); } public static Motorcycle getInstance() { if(_mInstance == null) { _mInstance = new Motorcycle(); } return _mInstance; } @Override public int Run() { // TODO Auto-generated method stub System.out.print("Motorcycle Run 30km/h at:"); return 30; } }
HighWay:
package com.jayfulmath.designpattern.bridge; public class HighWay extends Road { public HighWay(double _miles) { super(_miles); this.TAGNAME = "HighWay"; } @Override public double SpeedRate() { // TODO Auto-generated method stub System.out.println("In "+TAGNAME); return 1.5; } }
package com.jayfulmath.designpattern.bridge; public class Suburban extends Road { public Suburban(double _miles) { super(_miles); this.TAGNAME = "Suburban"; } @Override public double SpeedRate() { // TODO Auto-generated method stub System.out.println("In "+TAGNAME); return 1.0; } }
package com.jayfulmath.designpattern.bridge; public class CityRoad extends Road { public CityRoad(double _miles) { super(_miles); this.TAGNAME = "CityRoad"; } @Override public double SpeedRate() { // TODO Auto-generated method stub System.out.println("In "+TAGNAME); return 0.75; } }
汽车用简单工厂模式封装下：
package com.jayfulmath.designpattern.bridge; public class AutomobileFactory { public static Automobile CreateAutoMobile(int carType) { Automobile _mAuto = null; switch(carType) { case Automobile.TYPE_CAR: _mAuto = Car.getInstance(); break; case Automobile.TYPE_MOTORCYCLE: _mAuto = Motorcycle.getInstance(); break; } return _mAuto; } }
package com.jayfulmath.designpattern.bridge; import com.jayfulmath.designpattern.main.BasicExample; /*Bridge mode:当事物会随着很多方便变化而变化，我们可以把每个变化独立开来 * 对于不同的方面，可以进行相应的 * * */ public class BridgeMain extends BasicExample { @Override public void startDemo() { /*1.highway 50km car *2.cityWay 30km motorcycle *3.suburban 10km car * */ double h1 = getRunTime(Road.TYPE_HIGHWAY,Automobile.TYPE_CAR,50); double h2 = getRunTime(Road.TYPE_CITY,Automobile.TYPE_MOTORCYCLE,30); double h3 = getRunTime(Road.TYPE_SUBURBAN,Automobile.TYPE_CAR,10); System.out.println("Total time is "+(h1+h2+h3)); } private double getRunTime(int roadtype,int cartype,int pathlength) { double hour = 0; Road _mRoad = RoadFactory.CreateRoad(roadtype, pathlength); _mRoad.set_mAuto(AutomobileFactory.CreateAutoMobile(cartype)); hour = _mRoad.Run(); System.out.println("***************************************"); return hour; } }
结果：
distance of HighWay is 50 km Car Run 50km/h at:In HighWay HighWay spend time 0.67 hours *************************************** distance of CityRoad is 30 km Motorcycle Run 30km/h at:In CityRoad CityRoad spend time 1.33 hours *************************************** distance of Suburban is 10 km Car Run 50km/h at:In Suburban Suburban spend time 0.20 hours *************************************** Total time is 2.2
实现系统有多角度分类，每个角度都有可能变化，把它们独立开来，不用继承的方式，而是用聚合的方式，可以避免类的爆炸。