Collections Framework

Advantage of Collections over Arrays

• Collections are Grow-able in Nature
• Collection can hold heterogeneous data type. (An Interface type of Collection can be created)
• Collections are created based on some standard data structure

9 Key Interfaces of Collection Framwork

1. Collection
2. List
3. Set
4. SortedSet
5. NavigableSet
6. Queue
7. Map
8. SortedMap
9. NavigableMap

Collection Interface

• Most common methods applicable for almost all Interface is inside Collection Interface

Methods

• Query Methods
  • size()
  • contains()
  • iterator()
  • toArray()
• Modification Methods
  • add()
  • remove()
• Bulk Operations
  • containsAll()
  • addAll()
  • removeAll()
  • removeIf()
  • retainAll()
  • clear()
• Comparison and Hashing
  • equals()
  • hashcode()

Collection vs Collections

• Collection is an Interface (Root interface of collections)
• Collections is a Utility class used for collections. It contains method like searching and sorting

• Collection<I>
  • List<I>
    • ArrayList
    • LinkedList
    • Vector (Legacy)
      • Stack(Legacy)
  • Set<I>
    • HashSet
    • LinkedHashSet
    • SortedSet<I>
      • NavigableSet<I>
        • TreeSet
  • Queue<I>
    • Priority Queue
    • Blocking Queue<I>
      • PriorityBlockingQueue
      • LinkedBlockingQueue
• Map<I>
  • HashMap
    • LinkedHashMap
  • WeakHashMap
  • IdentityHashMap
  • Hashtable(Legacy)
    • Properties(Legacy)
  • SortedMap<I>
    • NavigableMap<I>
      • TreeMap

Other Classes :

• Sorting
  • Comparable<I>
  • Comparator<I>
• Cursor
  • Enumeration(Legacy)
  • Iterator
  • ListIterator
• Utility Classes
  • Collections
  • Arrays

Description :

• The java collections Framework defines several classes and interfaces which can be used to represent a group of individual object as a single entity.
• These classes and interface implement the collection data structures.
• For Example : list, stack, queue or maps.
• The collection framework was designed and developed primarily by Joshua Bloch
• It was introduced in JDK 1.2
• Why to use these collections?
  • We don’t have to implement every algorithm and data structure from the scratch, its already written into java.
  • It is already been tested.
• Almost all Collections are derived from the java.utils.Collection interface
• The main advantage of Collections over array is that collections are grow-able in size, i.e we need not know the size of elements in advance.
• toArray() method can transform any collection into one dimensional array.
• The Collection interface extends the java.lang.Iterable interface, this is why we can use for-each loop.

We write for each loop like below example :

for(String fruits : listOfFruits){
   System.out.println(fruits);
}

After compilation of .java file, .class file contains below code :

for (Iterator<String> i = listOfFruits.iterator(); i.hasNext();) {
   String fruits = i.next();
   System.out.println(fruits);
}