lesson 2 - collections and the java collections framework

8/14/2019 Lesson 2 - Collections and the Java Collections Framework

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Collections and the

Java CollectionsFramework


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Agenda

Collection Categories

Collection Operations

The JFC Collection Hierarchy


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Collection

Categories


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What is a collection? A collection is a group of elements that can

be treated as a single entity Types

Homogeneous

Requires that all of its elements be of the sametype Heterogeneous

Allows the elements to be of different types

Some collections allow the element type tobe a primitive type or an object, while some

are more restrictive Some collections allow duplicate elements

and others do not Some collections allow NULL elements and

others do not


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Collection Categories

Collections can be categorized by how the

elements they contain are organized

Linear

Hierarchical

Graph

Nonpositional


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Collection Category - Linear

Elements are arranged in sequence suchthat all elements except the first have a

unique predecessor and all except the lasthave a unique successor There are two ends to every linear

collection Linear collection may or may not allow null

or duplicate entries


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Collection Category Linear

Examples List

maintains a notion of position access (insertions, deletions, and retrievals) can be done at any

position in a list also known as a sequence

Stack all access are restricted to one end (top)

trays stacked in a cafeteria Back button of a browser makes use of a stack

Queue all insertion in which all insertions are done at one end (rear) all deletion are done at the other end (front)

People waiting to use an ATM machine


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Collection Category - Hierarchical

Trees Elements of a tree are called nodes A nonempty tree has a special node

called root, which has no predecessors(called parents) and zero or moresuccessors (called children)

Elements called leaves have oneparent and no children.

All other elements reside in the interior

of the tree and have one parent andone or more children

It cannot contain cycle


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Collection Category Hierarchical

Examples Tree

general hierarchical collection that does not specify howmany children an element may have

Binary Tree a binary tree is one in which a node can have no more

than two children

Binary Search Tree a binary search tree is a binary tree that orders its

elements to facilitate searching


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Collection Category - Graph Allows cycles An element can have zero or more

predecessors and zero or moresuccessors.

The elements of a graph are calledvertices and the connection betweenthem are edges.

Example Computer network topology

May or may not allow duplicate entries Undirected Graph

Two elements that are connected byan edge are both successor andpredecessor to one another

Directed Graph The edges clearly specify which mode

is the predecessor and which thesuccessor


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Collection Category Nonpositional

An unordered collection does not

recognize successors or predecessors

There is no notion of a position orsequencing in an unordered collection

Elements are inserted, found, and

removed based on some uniqueidentifying value


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Collection Category Nonpositional

Collection A collection is the most basic collection type

Duplicates are allowed Map

A map associates an entry with some unique,

identifying value

Example Student Record

Dictionary


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Collection

Operations


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Collection Operations

Adding an element Removing an element Replacing an element

Retrieving an element Determining whether an element is contained in a

collection Determining the size of a collection Testing to see whether the collection is empty Traversal Equality Cloning Serialization


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Java Collection Methods


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Java Collection Methods (cont)


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Java Collection

Framework


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What is a Java Collection

Framework? A collection framework is a software architecture

consisting of the following A hierarchy of interfaces that define various kinds of

collections and specifies how they are related A set of abstract classes that provide partial

implementation of the interfaces and serve as thefoundation for constructing concrete classes

A set of concrete classes based on different

underlying data structures (sometimes referred to asbacking stores) that offer different runtimecharacteristics

A set of algorithms that works with collections


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Java Collection Framework

Introduced with Java 2 platform

Provides implementations for a number of

common collections (list, maps, sets, stacksand vectors)

It also provides mechanisms to extend these

types to create new types (classes) that arealso part of the framework


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Advantages of working with a

collection framework It promotes code reuse

Use existing classes, rather than write from scratch Enables us to concentrate on other aspects of the problem to be

solved

It increases robustness and decreases debugging effort Any time we can use a class that has been used extensively and

can be regard as bug free We make our program more robust and reducing the amount of

code we will need to debug

It provides a mechanism for passing collections ofobjects among unrelated, and possibly independentlywritten, components The only requirement is that the collection object being passed

around is descended from Collection, the root of the collectionshierarchy


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Java Collection

FrameworkHierarchy


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Java Collection Framework

Hierarchy Collection

Provides the most general way to access acollection of elements

Duplicate elements within a collection areallowed

Elements are unordered, there is no notion ofthe position of an element

List Extends collection It allows duplicate elements and introduces an

ordering by supporting positional indexing Set

Extends Collection An unordered collection that does not allow

duplicates SortedSet

Extends Set A Set whose elements are sorted

Map Is the root of a separate hierarchy Deals with pairs instead of single

elements SortedMap

Extends Map A Map whose elements are sorted

lesson 2 - collections and the java collections framework

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