Collection Aima

8/16/2019 Collection Aima

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ADT

We can further extend the meaning of the ADT when applying itto data structures such as a stack and queue. In Java as with anyclass it means the data and the operations that can !e performedon it. In this context although even the fundamentals of how thedata is stored should !e invisi!le to the user. "sers not only

should not know how the methods work they should also notknow what structures are !eing used to store the data. #onsider for example the stack class. The end user knows that

push$% and pop$% $amoung other similar methods% exist and howthey work. The user doesn&t and shouldn&t have to know how

push$% and pop$% work or whether data is stored in an array alinked list or some other data structure like a tree.


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Java #ollection *ramework

Java collections framework The Java collections framework $J#*% is a set of classes and

interfaces that implement commonly reusa!le collection

data structures.+,-

Although it is a framework it works in a manner of a library. The J#* provides !oth

,. Interfaces that define various collections and . #lasses that implement them.

The #ollections *ramework provides a well/designed set ofinterfaces and classes for storing and manipulating groups of data asa single unit a collection.

http://en.wikipedia.org/wiki/Java_programming_languagehttp://en.wikipedia.org/wiki/Class_%28computer_science%29http://en.wikipedia.org/wiki/Interface_%28java%29http://en.wikipedia.org/wiki/Data_structurehttp://en.wikipedia.org/wiki/Java_collections_frameworkhttp://en.wikipedia.org/wiki/Software_frameworkhttp://en.wikipedia.org/wiki/Software_frameworkhttp://en.wikipedia.org/wiki/Java_collections_frameworkhttp://en.wikipedia.org/wiki/Data_structurehttp://en.wikipedia.org/wiki/Interface_%28java%29http://en.wikipedia.org/wiki/Class_%28computer_science%29http://en.wikipedia.org/wiki/Java_programming_language


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Java collection framework

The #ollection *ramework provides a set of interfacesand classes for represnting groups of data as an

a!straction called a #ollection.

(ava.util is a package Java.util.#ollection is the interface that is !ase of all

the interfaces of collection that expose operations like

adding removing and querying.

Java.util.A!stract#ollection is class that the foundationof all the #ollection framework classes. 3ee the figure

in next slide


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4ou can see #ollection interface is the !ase of another

interfaces like set list etc.

And A!stract#ollection class the !ase of another collection

class like A!stract5ist A!stract3et etc.


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Dynamic :inding

$late !inding virtual !inding% A mechanism !y which when the compiler can&t

determine which method implementation to use in

advance the runtime system $J;


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Introduction to #ollections


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#ollections

A collection is a structured group of o!(ects

Java ,. introduced the #ollections *ramework #ollections are defined in java.util

The #ollections framework is mostly a!out interfaces There are a num!er of predefined implementations

Java 0 introduced generics and =generici)ed> all the

existing collections Vectors have !een redefined to implement Collection

Trees linked lists stacks hash ta!les and other classes are

implementations of Collection

Arrays do not implement the Collection interfaces


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Types of #ollection

Java supplies several types of Collection? Set? cannot contain duplicate elements order is not important SortedSet? like a Set !ut order is important List? may contain duplicate elements order is important

Java also supplies some =collection/like> things? Map? a =dictionary> that associates keys with values order is not

important

SortedMap? like a Map !ut order is important

While you can get all the details from the Java A2I you are

expected to learn $i.e. memorize%? The signatures of the =most important> methods in each interface

The most important implementations of each interface


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The #ollections hierarchy


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SOFTENG 251

Ob ect Oriented

15

Interfaces

Root interface for operations

common to all types of collections

Specialises collection with

operations for FIFO and priority

queues.

Stores a sequence of elements,

allowing indexing methods

A special

Collection that

cannot contain

duplicates.

Special Set that retains

ordering of elements.

Stores mappings from keys to

values

Special map in

which keys are

ordered

Generalisation

Specialisation

Collection

Set List Queue

SortedSet

Map

SortedMap


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The Collection interface


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The "terator interface

An iterator is an o!(ect that will return the elements of acollection one at a time

interface Iterator boolean hasNext()

1eturns true if the iteration has more elements

E next() 1eturns the next element in the iteration

void remove() 1emoves from the underlying collection the last element returned !y

the iterator $optional operation%


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The Set interface

A set is a collection in which? There are no duplicate elements $according to equals% and @rder is not important

interface Set implements Collection, Iterable

The methods of Set are exactly the ones in Collection The following methods are especially interesting?

boolean contains(b!ect o) "" membership test boolean contains#ll(Collection c) ""subset test boolean add#ll(Collection c) "" union

boolean retain#ll(Collection c) "" intersection boolean remove#ll(Collection c) "" difference

add#ll retain#ll and remove#ll return true if the receiving setis changed and false otherwise


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The List interface

A list is an ordered sequence of elements interface %ist extends Collection, Iterable 3ome important %ist methods are?

void add(int index, E element)

E remove(int index) boolean remove(b!ect o) E set(int index, E element) E &et(int index) int indexf(b!ect o)

int lastIndexf(b!ect o) %istIterator listIterator()

A %istIterator is like an Iterator !ut has in addition has'revious andprevious methods


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Collection Iterate Example

hasnext$% and next$% In this section you will get the detailed explanation

a!out the next() method of interface Iterator. We are

going to use next() method of interface Iterator in Java.

The description of the code is given !elow for the usage

of the method.

21


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In the program code given !elow we have taken a string of elements. We have

converted this string of elements into a list of array and then we have applied the hasNext( method which returns true !ecause there are more elements in the list.

ence we get the following output.

import !ava."til.#$

p"blic class hasNext%

p"blic static void main (&trin' ar's) %

boolean b$

&trin' elements) * %+,l"e+- +rey+- +/eal+0$

&et s * new 1ash&et(Arrays.asList(elements$

Iterator i * s.iterator($

if (b * i.hasNext(%

&ystem.o"t.println(b$

0

0

0

22

C23"ni4"e5!avac hasNext.!ava

C23"ni4"e5!ava hasNext

tr"e

C23"ni4"e5


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In the program code given !elow we have taken a stringof elements. We have converted this string of elements

into a list of array and then we have applied the

hasNext( method first which will check if there is

another element or not and if there exist another element

then it will return that $next element% with the help of

next() method. ence we get the following output.

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import (ava.util.B9

p"blic class nextC

p"blic static void main $3tring args+-% C

3tring elements+- 8 C:lue Erey TealF9 3et s 8 new ash3et$Arrays.as5ist$elements%%9

Iterator i 8 s.iterator$%9

while $i.hasGext$%% C

3ystem.out.println$i.next$%%9 F

F

F

24


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C23"ni4"e5!avac next.!ava

C23"ni4"e5!ava next

,l"e

rey

/eal

C23"ni4"e5

25


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The SortedSet interface

A SortedSet is a Set for which the order of elements is important

interface SortedSet

implements Set, Collection, Iterable

Two of the SortedSet methods are? E first()

E last()


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2#

The Map interface

A map is a data structure for associating keys and values Interface ap

The two most important methods are? * put( +e, * value) adds a key/value pair to the map

* &et(b!ect +e) given a key looks up the associated value 3ome other important methods are?

Set +eSet() 1eturns a set view of the keys contained in this map.

Collection values() 1eturns a collection view of the values contained in this map


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2$

The SortedMap interface

A sorted map is a map that keeps the keys in sorted order Interface Sortedap

Two of the Sortedap methods are? firste()

laste()


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2%

Eenerics

public interface List {

void add(E x);

Iterator iterator();

public interface Iterator {

E next();

boolean !as"ext();

public interface #ap {

& put($ 'ey% & value);

Example 1 – Defining Generic Types:


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Why generic programming:ackground

old version ,. Java collections were Object /!ased andrequired the use of ugly casts cannot specify the exact type of elements

must cast to specific classes when accessing

Java generics

lets you write code that is safer and easier to read

is especially useful for general data structures such as

Array5ist

generic programming 8 programming with classes and

methods parameteri)ed with types


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Why generic programming $cont.% generic types are a powerful tool to write reusa!le o!(ect/

oriented components and li!raries however the generic language features are not easy to

master and can !e misused

their full understanding requires the knowledge of the typetheory of programming languages especially covariant and contravariant typing

the following introduces the main aspects of Java generics

and their use and limitations we mostly inspect illustrative samples of what is and what

is not allowed with some short glimpses inside the J;<

implementation


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Why generic programming $cont.%Java generics

in principle supports statically-tyed data structures early detection of type violations

cannot insert a string into Array5ist 6Gum!er7

also hides automatically generated casts suerficially resem!les #KK templates

#KK templates are factories for ordinary classes and

functions a new class is always instantiated for given distinct generic

parameters $type or other%

in Java generic types are factories for comile-time

entities related to types and methods


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Definition of a simple generic class class 2air 6T7 C

pu!lic T first9 pu!lic T second9

pu!lic 2air $T f T s% C first 8 f9 second 8 s9 F

pu!lic 2air $% C first 8 null9 second 8 null9 F

F you instantiate the generic class !y su!stituting actual

types for type varia!les as? 2air 63tring7

you can think the result as a class with a constructor pu!lic 2air $3tring f 3tring s% etc . .

you can then use the instantiated generic class as it

were a normal class $almost%?2air 63tring7 pair 8 new 2air 63tring7 $,%9


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Which #ollections do we haveL

There are two main interfaces for all the collection

types in Java:

Collection

ap


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#ollection "tils

,an%f*l Collection *tils appears as static metho%sof the class Collections:

http:''(ava)s*n)com'(avase'+'%ocs'api'(ava'*til'Collections)html

- similar set of *tils for simple arrays appear in the

class -rrays:

http:''(ava)s*n)com'(avase'+'%ocs'api'(ava'*til'-rrays)html


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3#

1estrictions and limitations in Java generic types are comile-time entities

in #KK instantiations of a class template are comiled searately as source code and tailored code is produced for

each one

primitive type parameters $2air 6int7% not allowed in #KK !oth classes and primitive types allowed

o!(ects in J;< have non/generic classes?2air63tring7 str2air 8 new 2air63tring7 . .9

2air6Gum!er7 num2air 8 new 2air6Gum!er7 . .9 ! 8 str2air.get#lass $% 88 num2air.get#lass $%9

assert ! 88 true9 !oth of the raw class 2air

!ut !yte/code has reflective info a!out generics


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3$

3ome implementations

class -ashSet implements Set class .reeSet implements SortedSet class #rra%ist implements %ist class %in+ed%ist implements %ist

class *ector implements %ist class Stac+ extends *ector

Important methods? push pop pee+ isEmpt

class -ashap implements ap class .reeap implements Sortedap

All of the a!ove provide a no/argument constructor


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Collection Aima

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