A Developer Gateway To IT World...

Techie Uncle Software Testing Core Java Java Spring C Programming Operating System HTML 5 Java 8 ES6 Project

Collection Framework in java

Collections in Java - techieuncle
The collection is a Java framework that provides the Collection Framework, which defines several classes and interfaces to represent a group of objects as a single unit.

Complete Overview of Collection Framework

If you want to repesent a group of objects in single entity, then we should go for collection interface.

(1.) If in this group of objects if duplicates are allowed, under some insertion order are preserved, in which order we insert object we save then the objects are save in same order, in such situation of programming we should go for List Interface and its implemented classes.

(2.) If in this group of objects if duplicates are not allowed and insertion order are not allowed then we should go for Set Interface and its implemented class.

List Interface: 

This interface is used to keep duplicate values and maintain insertion order.

Set Interface: 

This interface is used to remove duplicate values. 

Queue Interface:

This interface is used to FIFO based operation.

ArrayList class 
  •         It is Resizable-array.
  •         It is an implementation of the List interface.
  •         ArrayList implements all optional list operations, and permits all elements, including null.
  •         In addition to implementing the List interface, this class provides methods to manipulate the size of the array that is used internally to store the list.
  •         ArrayList class is roughly equivalent to Vector, except that it is unsynchronized.
  •         The sizeisEmptygetsetiterator, and listIterator operations run in constant time.
  •         The add operation runs in amortized constant time, it means that the adding n elements requires O(n) time.
  •         And roughly speaking we can say that all of the other operations run in linear time.
  •         The constant factor is low compared to that for the LinkedList implementation.
  •         Each ArrayList instance has a capacity.
  •         The capacity is the size of the array used to store the elements in the list.
  •         It is always at least as large as the list size.
  •         As elements are added to an ArrayList, its capacity grows automatically.
  •         The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost.
  •         An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation.
  •         This may reduce the amount of incremental reallocation.
  •         Note that this implementation is not synchronized. If multiple threads access an ArrayList instance concurrently, and at least one of the threads modifies the list structurally, it must be synchronized externally.
  •         (A structural modification is any operation that adds or deletes one or more elements, or explicitly resizes the backing array; merely setting the value of an element is not a structural modification.)
  •         This is typically accomplished by synchronizing on some object that naturally encapsulates the list.
  •         If no such object exists, the list should be "wrapped" using the Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:
  •         List list = Collections.synchronizedList(new ArrayList(...));
  •        The iterators returned by this class's iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException.
  •         Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.
  •         Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification.
  •         Fail-fast iterators throw ConcurrentModificationException on a best-effort basis.
    Source: Java Documentation by Eclipse