Java Q & A

1. What is the difference between

i.  List<Integer> list1 = new ArrayList<Integer>(Arrays.asList(ia));
ii. List<Integer> list2 = Arrays.asList(ia); 

i.  new ArrayList<Integer>(Arrays.asList(ia))

• The new ArrayList is an independent copy of the original one.
• Although you create the wrapper using Arrays.asList, it is used only during the construction of the new ArrayList and is garbage-collected afterwards.

ii. Arrays.asList(ia)

• Array ia and creates a wrapper that implements List<Integer>, which makes the original array as a list.
• Nothing is copied at all, only a single wrapper object is created.
• Operations on the list wrapper are propagated to the original array -- if you shuffle the list wrapper, the original array is shuffled; if you overwrite an element, it gets overwritten in the original array, etc.
• Some List operations aren't allowed on the wrapper, like adding or removing elements from the list -- no resize.
• list wrapper doesn't extend ArrayList -- ArrayLists have their own, internal array, which they are able to resize. 

2. Contructor of PriorityQueue

PriorityQueue(int initialCapacity, Comparator<? super E> comparator)

initialCapacity shouldn't < 1, otherwise, there will be IllegalArgumentException. 

3.