Collection is an important concept in java. The collection framework is a part of java.util package.The collection framework defines a set of interfaces and their implementation to manipulate collections. They serve as a container for a group of Objects such as a set of words in a dictionary or a collection of emails etc.The collection framework also allows us to store,retrieve and update a set of objects.
Advantages of collection:
- It is grow able in nature, based on programmer or application need , this can be increased or decreased.
- It can hold homogeneous or heterogeneous data
- Every collection is backed by some data structure [ready made data structure]
To overcome problem of array it is important to use collection.
Collection: Collection is way of representation of a group of objects as a single entity.In general collection interface is considered as root interface of collection framework.
Collection Framework: It is group of several classes and interfaces which can be used to represent a group of objects a single entity.
So basically a collection is a set of elements. Methods defined in a collection Interface as given as:
add(Object obj);// returns true if the object is added to the specified collection. adAll(Collection c);//returns true if the objects of the collection c are added to the specified collection. remove(Object obj);//returns true if the object is removed from the specified collection. removeAll(Collection c)//returns true if the objects of the collection c are removed from the specified collection. clear();//removes all elements from the specified collection contains(Object obj);////returns true if the collection contains the specified object. containsAll(Collection c);//Returns true if the collection contains all the elements in the specified collection. equals(Object obj);//Returns true if the specified object matches with the object in the collection. hashCode();//returns the hashcode of the collection. isEmpty();//Returns true if the collection is empty. iterator();Returns iterator over the elements in the collection. retainAll(Collection c);//Returns true if all the elements in a collection c is retrained in the specified //collection. size();//returns the number of elements in the collection. toArray();//returns an array containing all of the elements in the collection. toArray(Object object) ;//returns an array of objects if the array contains all the elements in the //specified collection.
add(),addAll() and remove() modify the collection objects.They may throw an Exception-UnsupportedOperationException when the collection does not support respective operation.
The methods of the collection interface will throw the ClassCastException if we add an incompatible element to a collection.(Some collection may not support null elements.)
Collection is an interface which can be used to represent a group of objects as a single entity.
Collections is an utility class found in java.util package to define several utility methods for collection objects.
The different frameworks are written below:
- Array..click here
- Collection..click here
- List…Click here
- ArrayList…Click here
- BitSet…..Click Here
- Sorted list
- Navigable set
- Queue…Click here
- Priority queue
- Blocking Queue
- Priority Blocking Queue
- Linked Blocking Queue
- Map….Click here
- Sorted Map
- Navigable Map
- HashMap…..Click Here
- Set…Click here
- Hashset…Click here
- Linked hashset
- Sorted Set…Click here
- Navigable set
- Dictionary..Click here
- HashTable…Click here
- Properties…Click here
- Iterator….Click here
The classes available in the collection framework implements the collection interface and the sub Interfaces. These classes also implement Map and Iterator Interfaces.
I am writing on these one by one.