Oop Handout Princple Programming Language

8/11/2019 Oop Handout Princple Programming Language

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Outline

1 OOP Introduction

2 Scala

PhD. Nguyen Hua Phung Object-Oriented Programming in Scala 2 / 2 9


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Object-Oriented Programming Goals

Programs as collections of collaborating objects

Object has public interface, hidden implementation

Objects are classfied according to their behavior

Objects may represent real-world entities or entities

that produce services for a program

Objects may be reusable across programs


I d i T OOP L


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Introduction To OOP Languages

There are many object-oriented programming (OOP)

languages

Some are pure OOP language (e.g., Smalltalk).

Newer languages do not support other paradigms but

use their imperative structures (e.g., Java and C).

Some support procedural and data-oriented

programming (e.g., Ada and C++).

Some support functional program (e.g., Scala)


S I t t F t f OOP


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Some Important Features of OOP

Abstract data types

Encapsulation

Information Hiding

Class Hierarchy

Inheritance

Polymorphism - Dynamic Binding


D t Ab t ti


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Data Abstraction

An abstract data type is data type that satisfies thefollowing two conditions:

Encapsulation:

Attributes and operations are combined in a single

syntactic unitcompiled separately

Information Hiding:

The access to members are controlled

Reliability increased


Information Hiding


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Information Hiding


ADT Example


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ADT Example

Operations on a stack:

create(stack)

destroy(stack)

empty(stack)

push(stack,element)pop(stack)

top(stack)

Client code:. . .c r e a t e ( s t k 1 ) ;push ( s t k1 , c o l o r 1 ) ;push ( s t k1 , c o l o r 2 ) ;

i f ( ! empty ( s t k1 ) )temp = t o p ( s t k 1 ) ;

. . .

Implementation can be adjacent or linked list. Client: dontcare!


Class Hierarchy


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Class Hierarchy

A class may have some Subclasses

A class may have one/many Superclass(es)

Animal

Fish

Whale

Mammal

Dog Cat

WingedAnimal

Bat

PhD. Nguyen Hua Phung Object-Oriented Programming in Scala 10/29

Inheritance


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Inheritance

A subclass is able to inheritnon-privatemembers ofits superclasses

A subclass can add its own members andoverrideits inherited members

Single vs. multiple inheritance

Inheritance increases the reusability in OOP


Diamond Problem in Multiple Inheritance


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Diamond Problem in Multiple Inheritance

A

B

D

C

if D inherits from B and C different versions of the

same behaviour, which version will be effective in D?

this problem, called diamond problem, is solveddifferently in different OO language

is there the diamond problem in Java?


Class vs Object; Method vs Message


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Class vs. Object; Method vs. Message

Class vs. Object

A class defines the abstract characteristics of a thing

its attributes or properties and

its behaviors or methods or features.

A Dog hasfurand is able to bark

An object is a particular instance of a class.

Lassie is a dog

Method vs. Message

A method describes a behavior of an object.

A dog can barkA message is a process at which a method of an

object is invoked.

Lassie barks


Polymorphism


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Polymorphism

Polymorphism: different objects can respond to the

same message in different ways.

Dynamic binding

Pointx,ydraw()move(newX,newY)

Circle radius

draw()

p.draw()


Other Concepts


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Other Concepts

There are two kinds of variables in a class:

Class variables

Instance variables

There are two kinds of methods in a class:

Class methods accept messages to the class

Instance methods accept messages to objects


Scala


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Scala

Invented by Martin Ordesky at EPFL, Lausanne,

Switzerland.

Similar to Java

Work smoothly with Java

Run on Java Virtual Machine

OOP + FP

Include lexer and parser generator


Classes and Objects in Scala


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Classes and Objects in Scala

Class

class [1]

abstract class [5]

trait [2]

case class [3]

Object

new

object


Example [7]


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Example [7]

class R a t io n a l ( n : I n t , d : I n t ) {r e q u ir e ( d ! = 0)

p r iv a te v al g = gcd ( n . abs , d . abs )p r iv a t e def gcd ( a : I n t , b : I n t ) : I n t =

i f ( b == 0 ) a else gcd ( b , a % b )va l numer = n / gva l denom = d / g

def t h is( n : I n t ) = t h i s( n , 1 )

def + ( t h a t : R at io na l ) : R at io na l =new R a t i o n a l (

numer t h a t . denom + t h a t . numer denom,denom that .denom

)

o v e rr i d e d ef t o S t r i n g = numer + " / " + denom}


Example on Abstract class [4]


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Example on Abstract class [4]

a b s tr a c t c la ss El em ent {

def c o n t en t s : A r ra y [ S t r i n g ] / / no body : abstractva l h e i g h t = c o n t en t s . l e n g t hva l w i dt h =

i f ( h e ig h t == 0) 0 else c o n t en t s ( 0 ) . l e n g t h}class A r ra y El e me n t ( c o n t s : A r r a y [ S t r i n g ] )

extends El em ent {def c o n t en t s : A r ra y [ S t r i n g ] = c o nt s

}class L in eE le men t ( s : S t r i n g )

extends A r ra y El e me n t ( A r r a y ( s ) ) {

o v e rr i d e d ef w id th = s . l e n gt ho v e rr i d e d ef h e i g ht = 1

}


Example on Object [1]


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a p e o Object [ ]

object Element {

def elem ( c o n t e n t s : A r r a y [ S t r i n g ] ) : El em en t =new ArrayEl em ent ( con t ent s )

def elem ( l i n e : S t r i n g ) : Element =

new L i ne E le me n t ( l i n e )}

va l space = Element . elem ( " " )va l h e l l o = E le me nt . elem ( A r r a y ( " h e l l o " , " w o r l d " ) )

Which kind of Element will be assigned tospaceand

hello?


Example on Case Class [3]


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p [ ]

a b s tr a c t c la ss Expr

case class Var ( name : S t r i n g ) extends Exprcase class Number (num : Double ) extends Exprcase class UnOp ( o p e r a t o r : S t r i n g , a rg : Ex pr )

extends Expr

case class BinOp ( o p e r a t o r : S t r i n g ,l e f t : Expr , r i g h t : Expr ) extends Expr

va l v = Var ( " x " )va l op = BinOp ( " + " , Number ( 1 ) , v )

v . nameop . l e f t


Example 1 on Traits [9]


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p [ ]

Reusability:

a b s tr a c t c la ss B i r d

t r a i t F l y i n g {def f ly Me ss : S t r i n gdef f l y ( ) = p r i n t l n ( f l yM es s )

}t r a i t Swimming {

def swim ( ) = p r i n t l n ( " I m swimming " )}class Penguin extends B i r d with Swimming

class Hawk extends B i r d with Swimming with F l y in g {

va l f ly Me ss = " I m a good f l y e r "}class F r i g a t e b i r d extends B i r d with F ly i n g {

va l f l yM es s = " I m an e x c e l l e n t f l y e r "}


Example 2 on Traits [2]


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p [ ]

Stackable Modifications:

a b s tr a c t c la ss I nt Qu eu e {

def g et ( ) : I n tdef pu t ( x : I n t ) }

class BasicIntQueue extends I nt Qu eu e {p r iv a te v al b u f = new A r r a y B u f f e r [ I n t ]def g e t ( ) = b u f . remove ( 0 )

def pu t ( x : I n t ) { b uf += x } }t r a i t Doubl ing extends I nt Qu eu e {a b st r a c t o v er r id e d ef p ut ( x : I n t ) { super . p u t ( 2 x ) } }

t r a i t I n c r e m e n t i n g extends I nt Qu eu e {a b st r a c t o v er r id e d ef p ut ( x : I n t ) { super . p u t ( x + 1 ) } }

va l queue =new BasicIntQueue with I n c r e m e n t i n g with Doubl ing

queue . put ( 10 )queue . g e t ( ) / / ? ? ?


Scala Hierarchy [8]


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y [ ]


Access Modifiers [6] in Scala


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publicprotected

private

protected[]

private[]

Example,

package Assignment. . .

protected[ Assignme nt ] v al f i e l d 1 = 100p r i v a t e[ t h i s ] va l f i e l d 2 = 2 ;


Summary


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What are still in your mind?


References


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[1] Classes and Objects,http://www.artima.com/pins1ed/classes-and-objects.html,19 06 2014.

[2] Traits, http://www.artima.com/pins1ed/traits.html,19 06 2014.

[3] Case Class and Pattern Matching,http://www.artima.com/pins1ed/case-classes-and-pattern-matching.html,19 06 2014.

[4] Abstract Members,http://www.artima.com/pins1ed/abstract-members.html,19 06 2014.

[5] Compositions and Inheritance,

http://www.artima.com/pins1ed/composition-and-inheritance.html,19 06 2014.[6] Packages and Imports,http://www.artima.com/pins1ed/packages-and-imports.html,19 06

2014.

[7] Functional Objects,http://www.artima.com/pins1ed/functional-objects.html,19 06 2014.

[8] Scala Hierarchy, http://www.artima.com/pins1ed/scalas-hierarchy.html,19 06 2014.

[9] Learning Scala part seven -Traits,http://joelabrahamsson.com/learning-scala-part-seven-traits/,19 06 2014.

http://www.artima.com/pins1ed/classes-and-objects.htmlhttp://www.artima.com/pins1ed/classes-and-objects.htmlhttp://www.artima.com/pins1ed/traits.htmlhttp://www.artima.com/pins1ed/traits.htmlhttp://www.artima.com/pins1ed/case-classes-and-pattern-matching.htmlhttp://www.artima.com/pins1ed/case-classes-and-pattern-matching.htmlhttp://www.artima.com/pins1ed/abstract-members.htmlhttp://www.artima.com/pins1ed/abstract-members.htmlhttp://www.artima.com/pins1ed/composition-and-inheritance.htmlhttp://www.artima.com/pins1ed/composition-and-inheritance.htmlhttp://www.artima.com/pins1ed/packages-and-imports.htmlhttp://www.artima.com/pins1ed/packages-and-imports.htmlhttp://www.artima.com/pins1ed/functional-objects.htmlhttp://www.artima.com/pins1ed/functional-objects.htmlhttp://www.artima.com/pins1ed/scalas-hierarchy.htmlhttp://www.artima.com/pins1ed/scalas-hierarchy.htmlhttp://joelabrahamsson.com/learning-scala-part-seven-traits/http://joelabrahamsson.com/learning-scala-part-seven-traits/http://joelabrahamsson.com/learning-scala-part-seven-traits/http://www.artima.com/pins1ed/scalas-hierarchy.htmlhttp://www.artima.com/pins1ed/functional-objects.htmlhttp://www.artima.com/pins1ed/packages-and-imports.htmlhttp://www.artima.com/pins1ed/composition-and-inheritance.htmlhttp://www.artima.com/pins1ed/abstract-members.htmlhttp://www.artima.com/pins1ed/case-classes-and-pattern-matching.htmlhttp://www.artima.com/pins1ed/traits.htmlhttp://www.artima.com/pins1ed/classes-and-objects.html

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Oop Handout Princple Programming Language