I wanted to use `Collection` for only single threaded environment and I am using a `HashMap` that is synchronized. 

However, I still doubt if it is thread safe to have it synchronized or not.
['https://Stackoverflow.com/questions/15152058', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/891556/']
1. the standard java HashMap is not synchronized.
2. If you are in a single threaded environment you don't need to worry about synchronization.
The commonly used `Collection` classes, such as `java.util.ArrayList`, are not synchronized. However, if there's a chance that two threads could be altering a collection concurrently, you can generate a synchronized collection from it using the `synchronizedCollection()` method. Similar to the read-only methods, the thread-safe APIs let you generate a synchronized collection, list, set, or map. For instance, this is how you can generate a synchronized map from a `HashMap`:

```
  Map map = Collections.synchronizedMap(new HashMap());
  map.put(...

```