Question

In some android open source code I found

 private Map<ImageView, String> imageViews=Collections.synchronizedMap(new
 WeakHashMap<ImageView, String>());

can any one explain me difference between Normal Map and collections.synchronizedmap

Answer 1

The regular Map implementations in java.util package are not thread safe. This means that if multiple threads are doing get() or put() operations on the same Map, it may result in race conditions or inconsistent data in the Map.

To use an existing Map in a multi-threaded environment, you can get a synchronized instance of the same by calling Collections.synchronizedMap(). On such instances, most of the methods like get(), put and keyset() are synchronized and can be safely used concurrently.

For more information on this, refer to
http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#synchronizedMap(java.util.Map)