交通灯管理系统

首先提取下这个问题的关键要素：交通灯，路，车。三者的一种关系是车可以认为是路的“元素”，车的通过和增加都是由路负责管理的。而每一个十字路口的放行与否，都是通过交通灯控制的。路和灯应该是归属的关系，一个十字路口“拥有”一个交通灯系统。

所以我们抽象交通灯这个类，因为向右是永远放行的，所以我们可以忽略向右的这条线路，而相反方向的灯的变化是完全相同的，所以可以抽象为一个管理系统，这样其实一个路口的交通等的状态就只有4种了，而且这四种同一时刻只有一个是放行的状态。

用枚举实现交通灯：

package traffic;  public enum Lamp {     NSStraight, NSTurn, EWStraight, EWTurn;          private boolean green = false;      public boolean isGreen() {         return green;     }      public void lighteOn() {         this.green = true;         System.out.println(this.toString());     }     public void lightOff(){         this.green = false;     }      Lamp nextLamp() {         switch (this) {         case NSStraight:             lightOff();             NSTurn.lighteOn();             return NSTurn;         case NSTurn:             lightOff();             EWStraight.lighteOn();             return EWStraight;         case EWStraight:             lightOff();             EWTurn.lighteOn();             return EWTurn;         case EWTurn:             lightOff();             NSStraight.lighteOn();             return NSStraight;         }         return null;     }     @Override     public String toString(){         switch (this) {         case NSStraight:             return "----------南北方向直行";         case NSTurn:             return "----------南北方向左转";         case EWStraight:             return "----------东西方向直行";         case EWTurn:             return "----------东西方向左转";         }         return null;              } }

交通灯的轮换相对来说比较独立，和路的耦合不算大，每个路口可以独立于路配备一个交通灯，这里先用线程实现模拟交通灯的切换规则：

package traffic;  public class LampControl implements Runnable{     Lamp NSStraight = Lamp.NSStraight;     Lamp NSTurn = Lamp.NSTurn;     Lamp EWStraight = Lamp.EWStraight;     Lamp EWTurn = Lamp.EWTurn;          Lamp currentLamp = NSStraight;          public Lamp getCurrentLamp() {         return currentLamp;     }          int StraightTime = 10000;//ms     int TurnTime = 10000;     @Override     public void run() {         currentLamp.lighteOn();         while(true){             try {                 Thread.sleep(StraightTime);                 currentLamp = currentLamp.nextLamp();                 Thread.sleep(TurnTime);                 currentLamp = currentLamp.nextLamp();                 Thread.sleep(StraightTime);                 currentLamp = currentLamp.nextLamp();                 Thread.sleep(TurnTime);                 currentLamp = currentLamp.nextLamp();                              } catch (InterruptedException e) {                 e.printStackTrace();             }         }                       }      }

这样在主函数中可以通过独立的线程模拟单独的交通灯切换功能。

接下来模拟十字路口的车辆过往的展示，一个十字路口有一个交通灯系统，抛开向右自由行驶的路线，有8条行车路线，每条路线用一个集合存放这条路线上的车，适当的时候放行。

package traffic;  import java.util.ArrayList; import java.util.List;  public enum SingleRoad {     NSRoad, SNRoad, NSLRoad, SNLRoad, EWRoad, WERoad, EWLRoad, WELRoad;     int num = 1;     List<Integer> list = new ArrayList<Integer>();      public void addCar() {         this.list.add(num++);             System.out.println(this.toString()+": "+num + "号车正在等待");     }      public void passCar() {         if(this.list.size()>0){             Integer i = this.list.remove(0);             System.out.println(this.toString()+": "+ i + "号车正在过马路");         }     }      @Override     public String toString() {         switch (this) {         case NSRoad:             return "北向南";         case SNRoad:             return "南向北";         case NSLRoad:             return "北向南左";         case SNLRoad:             return "南向北左";         case EWRoad:             return "东向西";         case WERoad:             return "西向东";         case EWLRoad:             return "东向西左";         case WELRoad:             return "西向东左";         }         return null;     }  }

在创建一个Road类管理一个十字路口的情形，随机的往每条线路上增加车辆并等待，当这条线路的控制灯亮的时候，放行这条线路上的车。

package traffic;  import java.util.ArrayList; import java.util.List; import java.util.Random;  public class Road implements Runnable {     LampControl lc = new LampControl();     List<SingleRoad> listRoads = new ArrayList<SingleRoad>();     SingleRoad NSRoad = SingleRoad.NSRoad;     SingleRoad SNRoad = SingleRoad.SNRoad;     SingleRoad NSLRoad = SingleRoad.NSLRoad;     SingleRoad SNLRoad = SingleRoad.SNLRoad;     SingleRoad EWRoad = SingleRoad.EWRoad;     SingleRoad WERoad = SingleRoad.WERoad;     SingleRoad EWLRoad = SingleRoad.EWLRoad;     SingleRoad WELRoad = SingleRoad.WELRoad;      public Road(LampControl lc) {         this.lc = lc;         listRoads.add(NSRoad);         listRoads.add(NSLRoad);         listRoads.add(SNRoad);         listRoads.add(SNLRoad);         listRoads.add(EWLRoad);         listRoads.add(EWRoad);         listRoads.add(WELRoad);         listRoads.add(WERoad);     }      void method(){         while(true){             Lamp l = lc.getCurrentLamp();             switch (l) {             case NSStraight:                 NSRoad.passCar();                 SNRoad.passCar();                 passTime();                 break;             case NSTurn:                 NSLRoad.passCar();                 SNLRoad.passCar();                 passTime();                 break;             case EWStraight:                 EWRoad.passCar();                 WERoad.passCar();                 passTime();                 break;             case EWTurn:                 EWLRoad.passCar();                 WELRoad.passCar();                 passTime();                 break;             }         }              }          private void passTime(){         try {             //一秒过一辆             Thread.sleep(1000);         } catch (InterruptedException e) {             e.printStackTrace();         }     }          @Override     public void run() {         while (true) {             try {                 //1--3秒随机添加一辆车                 Thread.sleep((new Random().nextInt(3) + 1) * 1000);             } catch (InterruptedException e) {                 e.printStackTrace();             }             int index = new Random().nextInt(8);             SingleRoad sr = listRoads.get(index);             sr.addCar();         }      }  }

这样当我们实际运行的时候就有三个线程了，一个线程专门负责灯的转换，一个线程专门负责车的添加，一个线程负责灯亮的时候车的放行。

public static void main(String[] args) {         LampControl lc1 = new LampControl();         Road road = new Road(lc1);         new Thread(lc1).start();         new Thread(road).start();         road.method();     }