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All the while, I am using ConcurrentHashMap, if I want to achieve the following.
ConcurrentModificationException, while another thread is modifying the map content.Sometime, I use enum as key, and from EnumMap Javadoc, I realize,
Iterators returned by the collection views are weakly consistent: they will never throw ConcurrentModificationException and they may or may not show the effects of any modifications to the map that occur while the iteration is in progress.
Hence, is it safe for me to replace
Map<Country, String> map = new ConcurrentHashMap<Country, String>();
with
Map<Country, String> map = Collections.synchronizedMap(new EnumMap<Country, String>(Country.class));
I know there is no putIfAbsent in EnumMap, but that is OK for me at this moment as I do not require it.
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EnumMap is much faster than HashMap. All keys of each EnumMap instance must be keys of the same enum type. EnumMap doesn't allow inserting null key if we try to insert the null key, it will throw NullPointerException. EnumMap is internally represented as arrays therefore it gives the better performance.
Java EnumMap is not thread-safe. You can make thread-safe by doing Collections.
Inserting null objects is not possible in ConcurrentHashMap as a key or value.
This is because the Collections. synchronizedMap() requires each thread to acquire a lock on the entire object for both read/write operations. By comparison, the ConcurrentHashMap allows threads to acquire locks on separate segments of the collection, and make modifications at the same time.
You can't do it for two reasons:
Collections.synchronizedMap are not synchronized).Iterator would be broken - you may get NoSuchElementException when calling next() after hasNext() returned true.
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