<< Chapter < Page Chapter >> Page >

According to The Java Tutorial from Oracle, a collection (sometimes called a container) is also an object that groups multiple elements into a single unit.

Typical collection objects might contain information about employees in the company telephone book, all the purchase orders issued during the past year, orthe transactions occurring in a person's checking account.

Slightly different terminology

Note that this terminology may be somewhat different from what you are accustomed to. For example, if you speak of your coin collection, you are probably speaking about the actual coins rather than the container that holdsthe coins.

This is an important distinction. The usage of the term collection in the Collections Framework usually refers to the container and not to the contents of the container. In the framework, the contents are usually referred to as the elements .

Store references rather than objects

The collections in the framework always store references to objects, rather than storing the objects themselves. One consequence of this is that primitivevalues cannot be stored in a collection without first encapsulating them in an object. (Standard wrapper classes are provided for encapsulating all primitive types.)

Stored as type Object

Furthermore, the references are always stored as type Object . Prior to Java version 1.5, when you retrieved an element from a collection, you frequently needed to downcastit before you could gain access to the members of the object to which the reference refers. Version 1.5 introduced Generics into the Java programming environment, which eliminated that requirement, (provided that you use the more complex syntax required by Generics) .

Moving data among methods

In addition to their use for storing, retrieving, and manipulating data, collections are also used to move data among methods.

One of the primary advantages of the Collections Framework is the ability to pass a collection to a method as the generic interface type Collection . The receiving method doesn't need to know the actual type of the object referredto by the incoming reference in order to call its methods.

Polymorphic behavior

The receiving method can call (on the reference to the Collection object) any of the methods declared in the Collection interface, with confidence that the behavior of the method will be appropriate for the actual type of Collection object involved. (That is polymorphic behavior.)

Core collection interfaces

If you have been working with the framework, you might be inclined to think that all of the interfaces in the following list are members of the core collection interfaces.

  • Collection
  • Set
  • List
  • Queue
  • Deque
  • SortedSet
  • Map
  • SortedMap
  • Iterator

However, that is not the case.

While the Iterator interface is heavily used in conjunction with collections, according to The Java Tutorial from Oracle, it is not one of the core collection interfaces.

The core collection interfaces identified by the Oracle book are shown below, with indentation showing the parent-child relationships among theinterfaces.

Questions & Answers

the diagram of the digestive system
Assiatu Reply
allimentary cannel
Ogenrwot
How does twins formed
William Reply
They formed in two ways first when one sperm and one egg are splited by mitosis or two sperm and two eggs join together
Oluwatobi
what is genetics
Josephine Reply
Genetics is the study of heredity
Misack
how does twins formed?
Misack
What is manual
Hassan Reply
discuss biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles
Joseph Reply
what is biology
Yousuf Reply
the study of living organisms and their interactions with one another and their environments
AI-Robot
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
Joseph Reply
what is the blood cells
Shaker Reply
list any five characteristics of the blood cells
Shaker
lack electricity and its more savely than electronic microscope because its naturally by using of light
Abdullahi Reply
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
Ramadan
What is classification
ISCONT Reply
is organisms that are similar into groups called tara
Yamosa
in what situation (s) would be the use of a scanning electron microscope be ideal and why?
Kenna Reply
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
Hilary
cell is the building block of life.
Condoleezza Reply
what is cell divisoin?
Aron Reply
Diversity of living thing
ISCONT
what is cell division
Aron Reply
Cell division is the process by which a single cell divides into two or more daughter cells. It is a fundamental process in all living organisms and is essential for growth, development, and reproduction. Cell division can occur through either mitosis or meiosis.
AI-Robot
What is life?
Allison Reply
life is defined as any system capable of performing functions such as eating, metabolizing,excreting,breathing,moving,Growing,reproducing,and responding to external stimuli.
Mohamed
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?

Ask