Collection Framework

-
Collection Framework provides classes and interfaces that can be used to represent collections i.e. a group of objects.

Interfaces in the Collection Framework
Following are the interfaces provided by the Collection Framework :

1. Collection :
- defines the most common methods which are applicable for any Collection object.

2. List :
- Child interface of Collection.
- represents group of objects
- duplicates allowed
- order of insertion preserved
- Child classes : ArrayList, LinkedList, Vector->Stack

3. Set : 
- Child interface of Collection.
- represents group of objects
- unique elements i.e. duplicates not allowed
- insertion order not preserved
- Child classes : HashSet, LinkedHashSet

4. SortedSet :
- Child interface of Set
- represents group of objects
- unique elements i.e. duplicates not allowed
- elements stored in a sorted order

5. NavigableSet :
- Child interface of SortedSet
- provides methods for navigating through the elements
- Child classes : TreeSet (before introduction of NavigableSet, this was a child of SortedSet)

6. Queue :
- Child interface of Collection
- data structure which permits removal of objects only from the head.
- Child Classes : PriorityQueue, BlockingQueue->LinkedBlockingQueue, PriorityBlockingQueue

7. Map :
- represents objects as key-value pairs
- Not a child of Collection interface
- duplicate keys not allowed
- Child classes : HashMap->LinkedHashMap, WeakHashMap, IdentityHashMap, Hashtable->Properties

8. SortedMap :
- Child interface of Map
- represents key-value pairs where keys are sorted in some order.

9. NavigableMap :
- Child interface of SortedMap
- provides methods for navigating through the objects in the map
- Child classes : TreeMap (before introduction of NavigableMap in 1.6 version, this was a child of SortedMap)

Map interface hierarchy is similar to Set hierarchy. Map->SortedMap->NavigableMap; Set->SortedSet->NavigableSet

Apart from the above interfaces, Collection framework provides Comparable and Comparator interfaces for sorting the objects. For iterating over the objects, it provides Enumeration, Iterator, and ListIterator interfaces.

Collections and Arrays are the utility classes that provide utility methods that can be used on collection objects and array objects respectively. e.g. Collections.sort() or Arrays.sort()


Image result for collections framework hierarchy

Comments

Post a Comment

Popular posts from this blog

Collection Framework - HashSet And LinkedHashSet class

-
As ArrayLists use arrays as the underlying storage, in case of HashSet, hashtable is the datastructure that was implemented. HashSet stores objects based on their hashcodes. Duplicates are not allowed and since its stored based on hashcode, insertion order is not preserved. Hashing data structures comes with a initial capacity of 16  i.e. 2 power 4. There is one more terminology with regards to hashing data structures, load factor , i.e. when should a new hashset be created with double the capacity. Default load factor is 0.75 i.e. when 75% hashset is filled, a new larger hashset is created. HashSet comes with the following constructors : HashSet() - creates a hash set with a default initial capacity of 16 and load factor 0.75 HashSet(int initialCapacity) - creates a hash set with the specified initial capacity and load factor 0.75. HashSet(int initialCapacity, int loadFactor) - creates a hash set with the specified initial capacity and the specified load factor HashSet(
Read more

Collection Framework - Cursors in Java

-
Java provides interfaces that are implemented by collection classes so that we can fetch elements one by one or iterate through the elements in the collection. The cursors provided by Java are : 1. Enumeration 2. Iterator 3. ListIterator 4. SplitIterator(introduced in Java 8) Before the introduction of cursors, what was the way we used to iterate through the collection? The traditional for loop!!! for(int i=0; i< coll.size;i++) {      System.out.println(coll.get(i)); } Enumeration It is a legacy interface that provides us the facility to traverse through the elements of the legacy classes one by one. The example for enumeration can be found  here Iterator Enumeration has 2 limitations : 1. Its only applicable to legacy classes 2. We do not have an option to remove element from collection while traversing The above two limitations were overcome by introduction of Iterator. Iterator is a universal cursor i.e. it is applicable to all the classes in the collecti
Read more

Hashed data structures

-
Image
Introduction Common way of indexing data is by using hash maps which we use to map keys to values. The indexing of keys to values is built by using a hash function to compute which bucket or location our data will be stored in. If two pieces of data are hashed to the same location, it is called "collision". The Hash Function A hash function is basically a function that takes arbitrary data and returns a fixed length output. We usually call the output of a hash function as hash code. It is one of the most widely used data structures in modern programming. Properties of a hash function : 1. Deterministic :- A given input always generates the same output 2. Uniform :- The output should be probable in a given range  public long DJBHash(String str)    {       long hash = 5381;       for(int i = 0; i < str.length(); i++)       {          hash = ((hash << 5) + hash) + str.charAt(i);       }       return hash;    } Perfect Hashing
Read more