多线程操作---委托线程安全
1.使用复制来保证线程安全

class MonitorVehicleTracker{private final Map<String,MutablePoint> locations;public MonitorVehicleTracker(Map<String,MutablePoint> locations){this.locations = deepCopy(locations);}public synchronized Map<String,MutablePoint> getLocations(){//我拥有的是外界传给我的拷贝，所以外界的locations改变了也不会影响我return deepCopy(locations);}public synchronized MutablePoint getLocation(String id){MutablePoint loc = locations.get(id);//传出去的也是一份拷贝，也意味着通过这个方法，外界只能看locations里面的数据，而不能改return loc==null?null:new MutablePoint(loc);}public synchronized void setLocation(String id,int x,int y){//只能通过这个接口才能改location数据，保证了修改的可控性MutablePoint loc = locations.get(id);if(loc==null)throw new IllegalArgumentException("No such ID:"+id);loc.x=x;loc.y=y;}private static Map<String ,MutablePoint> deepCopy(Map<String,MutablePoint> m){Map<String ,MutablePoint> result = new HashMap<String,MutablePoint>();for(String id:m.keySet())result.put(id,new MutablePoint(m.get(id)));return Collections.unmodifiableMap(result);//这个map不允许增加或者减少元素}}class MutablePoint{public int x,y;public MutablePoint(){x=0;y=0;}public MutablePoint(MutablePoint p){this.x=p.x;this.y=p.y;}}

class MonitorVehicleTracker{private final Map<String,MutablePoint> locations;private final Map<String,MutablePoint> unmodifiableMap;public MonitorVehicleTracker(Map<String,MutablePoint> locations){this.locations = new ConcurrentHashMap<String,MutablePoint>(locations);this.unmodifiableMap = Collections.unmodifiableMap(locations);}public /*synchronized*/ Map<String,MutablePoint> getLocations(){ return this.unmodifiableMap;}public /*synchronized*/ MutablePoint getLocation(String id){return locations.get(id);}public /*synchronized*/ void setLocation(String id,int x,int y){ MutablePoint loc = locations.get(id);if(loc==null)throw new IllegalArgumentException("No such ID:"+id);loc.set(x, y); //只有这一小段同步了}private static Map<String ,MutablePoint> deepCopy(Map<String,MutablePoint> m){Map<String ,MutablePoint> result = new HashMap<String,MutablePoint>();for(String id:m.keySet())result.put(id,new MutablePoint(m.get(id)));return Collections.unmodifiableMap(result);//这个map不允许增加或者减少元素}}class MutablePoint{public int x,y;public MutablePoint(){x=0;y=0;}public MutablePoint(MutablePoint p){this.x=p.x;this.y=p.y;}public synchronized void set(int x,int y){this.x=x;this.y=y;}}