Set
- AbstractSet, CopyOnWriteArraySet, EnumSet, HashSet, JobStateReasons, LinkedHashSet, TreeSet

List
- AbstractList, AbstractSequentialList, ArrayList, AttributeList, CopyOnWriteArrayList, LinkedList, RoleList, RoleUnresolvedList, Stack, Vector

Queue
- AbstractQueue, ArrayBlockingQueue, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingQueue, LinkedList, PriorityBlockingQueue, PriorityQueue, SynchronousQueue

Map
- AbstractMap, Attributes, AuthProvider, ConcurrentHashMap, EnumMap, HashMap, Hashtable, IdentityHashMap, LinkedHashMap, PrinterStateReasons, Properties, Provider, RenderingHints, TabularDataSupport, TreeMap, UIDefaults, WeakHashMap

Collection에 들어있는 오브젝트를 가져오기 위해서 일반적으로 Iterator 패턴을 구현한 Iterator 클래스를 많이 사용합니다. 하지만, Iterator클래스의 next()를 통해서 오브젝트를 가져오고, hasNext()를 통해서 오브젝트의 마지막을 체크하기 때문에, List 타입의 Collection에서는 get()를 사용하는 것이 더 빠르게 동작을 합니다.

ex) Iterator 클래스 사용예

Iterator iterator = array.iterator();
while (iterator.hasNext()) {
 Object object = iterator.next();
}

ex) List 타입의 get() 사용 예

int size = array.size();
for (int i=0; i<size ; i++) {
 Object object = array.get(i);
}

출처는 http://satukubik.com/2007/12/19/java-tips-initializing-collection/ 입니다.

Especially in unit test, we have to initialize an array or a collection. Well, for array, it’s OK… A simple code that we know can solve the problem:

String[] s = new String [] {"1", "2"};

But how about Collection? Normal way to initialize collection is something like this (which pretty ugly):

List<String> s = new ArrayList<String>();
s.add("1");
s.add("2");

I hardly find an elegant solution until I see this post. There are at least three better solution for the case.

First solution:

List<String> s = new ArrayList<String>() {{ add("1"); add("2"); }};

Which unfortunately, doesn’t pass Java Code Convention (that is, if you format the code, it will become uglier than the original).

List<String> s = new ArrayList<String>() {
   {
      add("1");
      add("2");
   }
};

Second solution:

List<String> s = Arrays.asList(new String[]{"1", "2"});

This solution is the best if you use Java 1.4 or before. But if you use Java 5, the third is more elegant:

List<String> s = Arrays.asList("1", "2");

Great!

EDIT: Rob Juurlink commented that this solution will create a fixed read only collection, so you may want to wrap it with ArrayList (or other Collection class) to make it writable