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- Collection is an object representing a group of objects.
- Collection framework contains a set of classes and interfaces which are used for representing and manipulating collections.
- Collection interface is the root interface from which the interfaces List, Set,Queue are extended.
List interface:
- List interface is an ordered collection in which duplicate elements are also allowed.
- Elements are stored in a sequential way and hence its elements can be accessed using the index value.
- ArrayList
- LinkedList
- Vector
Set interface:
- Set is an unordered collection. It does not maintain any order while storing the elements. It does not allow duplicate elements.
Thus if one requires to store a group of unique elements, set can be used.
- HashSet
- LinkedHashSet
- TreeSet
Map interface:
- Map is an interface which maps keys to values in which each key has to be unique.
- HashMap
- Hashtable
- TreeMap
Retrieving elements from collection:
Iterator interface:
- Iterator interface is used to iterate over a collection object and retrieve the elements one after the other.
ListIterator interface:
- ListIterator is similar to Iterator interface except that the elements of the collection can be retrieved from both forward and backward direction.
Enumeration interface:
- Enumeration interface is similar to Iterator interface except that it cannot remove elements and can only iterate over the collection object.
Iterating using enhanced for loop:
- Enhanced for loop can also be used to iterate over the collection object.
Example:
| List<String> places= new LinkedList<String>();
for(String place: places) System.out.println(“Place:”+place); |