Quick Notes : Practical usage of collections

Different Types of Collections and when to Use them

Set

HashSet : 

• When you want unique set to objects. 
• Make sure equals and hashcode is implemented.
• This does not maintain the order of object addition. As the name says it is Hashed

TreeSet:

• You can have the list ordered the way you want, by passing in a comparator.
• Example: new TreeSet(String.CASE_INSENSITIVE_ORDER)
• It automatically orders the objects that you add accordingly

LinkedHashSet

• This gives us the flexibility of HashSet (uniqueness) and 
• also maintains the insertion-order of objects

Map

HashMap :

• Easier way of holding Key Value Pair
• Does not maintain the insertion-order (Hashed)

TreeMap:

• Sorted Map, Sorting of keys determined by the comparator in the constructor
• Quickly create a map of case insensitive keys as follows
  new TreeMap(String.CASE_INSENSITIVE_ORDER)
• Throws a NullPointerException if you use get without a null check.
  treemap.get(null), so better add a null check before invoking get()

LinkedHashMap:

• Extends HashMap. But, preserves of the insertion order

List:

ArrayList:

• Quicker way of maintaining a list of objects
• can add duplicate values.
• It is advisable to use this collection if we expect more number of gets() than add() or set()

LinkedList:

• Performs better when you have more additions and insertions than searching the list