How fast-fail happened in non-synced collections
(why modCount is not volatile: http://www.jianshu.com/p/d9ee4b075d5a )
Differences between Iterator and ListIterator
Methods of Iterator (for list and set):
hasNext()
next()
remove()
Methods of ListIterator (only for list):
add(E e)
hasNext()
hasPrevious()
next()
nextIndex()
previous()
previousIndex()
remove()
set(E e)
ReentrantLock and synchronized
ReentrantLock has bettern performance and can cross method.
But synchronized is simple. So use it unless it is proven to be a problem.
Enumeration and Iterator
Enumeration is faster than Iterator since Iterator may check fast fail while Enumeration don’t. Iterator also support modification. Enumeration is usually used in synced collection.
Queue
Non-blocking
Dequeue (LinkedList and ArrayDeque are its children)
PriorityQueue (maintains a binary heap)
Blocking (see notes on Concurrency)
ArrayBlockingQueue
LinkedBlockingQueue
PriorityBlockingQueue
DelayedWorkQueue (in ScheduledThreadExecutor, this is actually also a binary heap)
DelayQueue (very similar to DeplayedWordQueue)
Set
HastSet 和 TreeSet 是Set的两个实现类。
HashSet依赖于HashMap，它实际上是通过HashMap实现的。HashSet中的元素是无序的。
TreeSet依赖于TreeMap，它实际上是通过TreeMap实现的。TreeSet中的元素是有序的。
Synchronized collections
CopyOnWriteArrayList
Vector/Stack
HashTable
ConcurrentHashMap
Collections.synchronizedXXX()
Difference between HashTable, ConcurrentHashMap and Collections.synchronizedMap
The “scalability issues” for Hashtable are present in exactly the same way in Collections.synchronizedMap(Map) - they use very simple synchronization, which means that only one thread can access the map at the same time.