CSG2H3 Object Oriented Programming. Polymorphism -RSM-

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CSG2H3

Object Oriented Programming

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The ability of objects belonging to different

types to respond to method calls of the same

name, each one according to an appropriate

type-specific behavior [Wikipedia].

The ability of a variable entity or data

structure element, at run time, to become

attached to objects of different types [Meyer].

A concept where a single name may denote

objects of different classes that are related by

some common base class [Booch].

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Kemampuan suatu objek untuk digunakan di

banyak tujuan berbeda dengan nama yang sama.

Kemampuan objek dalam memberikan respon

yang berbeda terhadap message yang mempunyai

nama yang sama.

Kemampuan untuk mempunyai beberapa bentuk

yang berbeda.

Disebut juga:

–

dynamic binding

–

late binding

–

run-time binding

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// Program Utama

class TesPoligon {

Poligon p = new Poligon();

...

SegiEmpat s = new SegiEmpat();

SegiTiga t = new SegiTiga();

Lingkaran l = new Lingkaran();

p = s;

// ok krn instan kelas

anak juga instan kelas induk

...

}

Gambaran Polimorfisme

Poligon

SegiEmpat SegiTiga Lingkaran

variabel p menunjuk

objek yang diciptakan

dari kelas Poligon _{variabel s menunjuk}

objek yang diciptakan dari kelas SegiEmpat

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Gambaran Polimorfisme

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Poligon SegiEmpat p s

Poligon p = new Poligon();

SegiEmpat s = new SegiEmpat();

Sebelum:

Poligon SegiEmpat p s

p = s;

Sesudah:

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0 6 R E V IS E D 8 FE B 2 0 1 3 class SegiEmpat { . . .

public String display() { return ("Segi Empat"

+ "\no Panjang : " + getPanjang() + "\no Lebar : " + getLebar() + "\no Luas : " + Luas()

+ "\no Keliling : " + Keliling()); }

}

Gambaran Polimorfisme [3]

class Lingkaran { . . .

public String display() { return (“Lingkaran"

+ "\no jari-jari: " + getRadius() + "\no Luas : " + Luas()

+ "\no Keliling : " + Keliling()); }

}

class TesPoligon {

public static void main(String args[]) {

// Deklarasi array

Poligon[] p = new Poligon[3]; // Add array poligon

p[0] = new SegiEmpat(17, 8); p[1] = new Segitiga(21,4) p[2] = new Lingkaran(10); // Display informasi

for (int i=0; i<p.length; i++) {

System.out.println(p[i].display()); }

} }

Method display () yang dieksekusi ditentukan berdasarkan rujukan ke

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Gambaran Polimorfisme [4]

Hasil eksekusi method

displayInfo()

yang dipunyai

masing-masing objek

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Overloading

–

Method

–

Constructor

Overriding

Pendefinisian ulang method yang diturunkan kelas

induk oleh kelas anak.

Coercion & Casting

Sub-type Polymorphism

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Menuliskan kembali method dengan nama yang

sama pada suatu class.

Tujuan : memudahkan penggunaan/ pemanggilan

method dengan fungsionalitas yang

mirip

.

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Nama method harus sama

Daftar parameter harus berbeda

Return type boleh sama, juga boleh berbeda

Aturan Pendeklarasian Method

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Daftar Parameter pada Method

Overloading

Perbedaan daftar parameter bukan hanya terjadi pada

perbedaan banyaknya parameter, tetapi juga urutan dari

parameter tersebut.

Misalnya saja dua buah parameter berikut ini :

–

function_member(int x, String n)

–

function_member(String n, int x)

Dua parameter tersebut juga dianggap berbeda daftar

parameternya.

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Daftar Parameter pada Method

Overloading

Daftar parameter tidak terkait dengan

penamaan variabel yang ada dalam

parameter.

Misalnya saja 2 daftar parameter berikut :

–

function_member(int x)

–

function_member(int y)

Dua daftar parameter diatas dianggap sama

karena yang berbeda hanya penamaan

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Contoh Method Overloading

public class Bentuk {

…

public void Gambar(int t1) {

…

}

public void Gambar(int t1, int t2) {

…

}

public void Gambar(int t1, int t2, int t3) {

…

}

public void Gambar(int t1, int t2, int t3, int t4) {

…

}

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Overloading juga bisa terjadi antara parent class

dengan subclass-nya jika memenuhi ketiga syarat

overload.

Misalnya saja dari class Bentuk pada contoh

sebelumnya kita turunkan sebuah class baru yang

bernama WarnaiBentuk.

Method Overloading antara Parent Class

& Sub Class

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public class WarnaiBentuk extends Bentuk {

public void Gambar(String warna, int t1, int t2, int3) {

…

}

public void Gambar(String warna, int t1, int t2, int3, int t4){

…

}

…

}

Method Overloading antara Parent Class

& Sub Class

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Constructor Overloading

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Subclass yang berusaha memodifikasi tingkah laku yang

diwarisi dari superclass.

Tujuan: subclass memiliki tingkah laku yang lebih

spesifik.

Dilakukan dengan cara mendeklarasikan kembali method

milik parent class di subclass.

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Deklarasi method pada subclass harus sama dengan

yang terdapat di super class. Kesamaan pada:

–

Nama

–

Return type

–

Daftar parameter (jumlah, tipe, dan urutan)

Method pada parent class disebut overriden method

Method pada subclass disebut overriding method.

Overriding

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public class Employee { protected String name; protected double Salary; protected Date birthday;

public String getDetails(){ return “Name:

“+name+”\n”+”Salary: “+salary; }

}

public class Manager extends Employee{

protected String department;

public String getDetails(){ return “Name: “+name+”\n”+”Salary: “+salary+”\n”+”Manager of: “+department; } }

Contoh Overriding

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public class Animal {

public void SetVoice() {

System.out.println(“Blesepblesep”);

}

public class Dog extends Animal {

public void SetVoice() {

System.out.println(“Hug hug”);

}

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Aturan Overriding

Mode akses overriding method harus sama

atau lebih

luas

dari pada overriden method.

Subclass hanya boleh meng-override method

superclass satu kali saja, tidak boleh ada lebih

dari satu method pada kelas yang sama yang

sama persis.

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Casting

taking an Object of one particular type and

“turning it into” another Object type

Type Casting

Object Casting

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Type Casting

Assigning a value of one type to a variable of another

type

Widening Casting

–

Smaller type to larger type

–

Implicit

–

Automatic type conversion

–

The two types must compatible

–

The target type is larger than the source

type

Narrowing Casting

–

Larger type to smaller type

–

Explicit

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Implicit type conversion, supplied automatically

by programming language even if the

programmer leaves it out

Explicit type conversion in Java:

double x;

x = (double) 2;

Coercion in Java

double x;

x = 2;

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Contoh Parameter Coercion/ Widening Casting

void f(double x) {

…

}

f((byte) 1);

f((short) 2);

f('a');

f(3);

f(4L);

f(5.6F);

This

f

can be called with any

type of parameter.

Java is willing to coerce to

type

double

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Contoh Parameter Coercion/ Widening Casting

public class Driver{

public static void main(String args[]){

int i = 50;

long l = i; float f = l;

System.out.println(“int value: “ + i); System.out.println(“long value: “ + l); System.out.println(“float value: “ + f); } } > int value: 50 > long value: 50 > float value: 50.0

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Narrowing Casting

public static void main(String args[]){

double d = 25.16;

long l = (long)d; int i = (int)l;

System.out.println(“double value: “ + d); System.out.println(“long value: “ + l); System.out.println(“int value: “ + i);

} }

> double value: 25.16 > long value: 25

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Object Casting

Turn an object of a class to another class

Both classes should have inheritance or implement

relationship

Upcasting

–

Implicit

–

Assign subclass object to a super class object

Downcasting

–

Explisit

–

Assign a super class object to a subclass object

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Virtual Method Invocation

Virtual method invocation is the form of

Upcasting

At the time of the object that has been created

calling overridden method in the parent class, the

Java compiler will do the invocation (call) to the

overriding method in a subclass, which is

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Example

public class Parent{

public String toString(){

return “this is class Parent”;

}

public class ChildA extends Parent{

return “this is class Child A”;

}

public class ChildB extends Parent{

return “this is class Child B”;

}

public class GrandChildA extends ChildA{

return “this is class Grand Child”;

}

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Example

> this is method Parent > this is method Child A > this is method Child B > this is method Grand Child

public static void main(String args[]){ Parent p = new Parent();

ChildA cA = new ChildA(); ChildB cB = new ChildB();

GrandChildA gC = new GrandChildA(); System.out.println(p.toString()); System.out.println(cA.toString()); System.out.println(cB.toString()); System.out.println(gC.toString()); } }

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Example Upcasting/VMI

> this is method Parent > this is method Child A > this is method Child B > this is method Grand Child

public static void main(String args[]){ Parent castP;

castP = new Parent();

System.out.println(castP.toString()); castP = new ChildA();

System.out.println(castP.toString()); castP = new ChildB();

System.out.println(castP.toString()); castP = new GrandChildA();

System.out.println(castP.toString()); }

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Example Upcasting/VMI

> this is method Grand Child > this is method Child B

GrandChildA gC = new GrandChildA(); ChildB cB = new ChildB();

castP = gC; System.out.println(castP.toString()); castP = cB; System.out.println(castP.toString()); } }

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Upcasting

castP

=

new ChildA

();

Object castP has a behavior that is in accordance

with the runtime type, not the compile type

When compile-time castP is a Parent

When runtime castP is ChildA

Therefore

–

castP can only access variable Parent

–

castP can only access method ChildA

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Example

public class Parent{

protected int number = 10;

return “Parent ” + number;

}

public class ChildA extends Parent{

return “Child A ” + number;

}

public String methodA(){

return “method Child A”;

} }

public class ChildB extends Parent{

return “Child B ” + number;

}

public String methodB(){

return “method Child B”;

public class GrandChildA extends ChildA{

return “Grand Child ” + number;

}

public String methodGrand(){

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Example

> Parent 10 > Child A 20 > Child B 30 > Grand Child 40

GrandChildA gC = new GrandChildA(); System.out.println(p.toString()); System.out.println(cA.toString()); System.out.println(cB.toString()); System.out.println(gC.toString()); } }

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Example

> Child A 20 > 10 > Grand Child 40 > 10

GrandChildA gC = new GrandChildA(); Parent castP; castP = cA; System.out.println(castP.toString()); System.out.println(castP.number); castP = gC; System.out.println(castP.toString()); System.out.println(castP.number); } }

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Example

> method Child A

GrandChildA gC = new GrandChildA(); Parent castP; System.out.println(cA.methodA()); castP = cA; System.out.println(castP.methodA()); } }

//compile error:

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DownCasting

Return the upcasted object back to its original

class object

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Example

> Grand Child 40 > Compile error > Grand Child 40 > Method Child A

> Method Grand Child A > Grand Child 40

> Method Child A

castP = new GrandChildA();

System.out.println(castP.toString()); System.out.println(castP.methodA());

GrandChildA castG; //castG = castP;

castG = (GrandChildA) castP;

System.out.println(castG.toString()); System.out.println(castG.methodA()); System.out.println(castG.methodGrand()); ChildA castA = (ChildA) castP;

System.out.println(castA.toString()); System.out.println(castA.methodA());

} }

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Example

> Grand Child 40 > Method Child A

> Method Grand Child A

castP = new GrandChildA();

System.out.println(castP.toString()); System.out.println( ((ChildA)castP).methodA() ); System.out.println( ((GrandChildA)castP).methodGrand() ); } }

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Example

> Child B 30 > ClassCastException

ChildA castA; GrandChildA gC;

castP = new ChildB();

System.out.println(castP.toString()); castA = (ChildA)castP; System.out.println(castA.toString()); System.out.println(castA.methodA()); } }

//runtime error:

Class Cast Exception

Downcast only to

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Example

> Child A 20 > ClassCastException

castP = new ChildA();

System.out.println(castP.toString()); gC = (GrandChildA)castP; System.out.println(gC.toString()); System.out.println(gC.methodA()); System.out.println(gC.methodGrand()); } }

//runtime error:

Class Cast Exception

Downcast only to

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Downcasting

Before doing downcasting, upcasting must be

done

Can only downcast to original class or its parents’

class

To check whether the object can be casted

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Keyword instanceof

Used to test if an object is of a specified type

–

test if an object is an instance of a class,

–

an instance of a subclass,

–

or an instance of a class that implements a particular

interface

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Example

System.out.println("p instanceof Parent: " + (p instanceof Parent));

System.out.println("p instanceof ChildA: " + (p instanceof ChildA));

System.out.println("cA instanceof Parent: " + (cA instanceof Parent));

System.out.println("cA instanceof ChildA: " + (cA instanceof ChildA));

System.out.println("cB instanceof ChildA: " + (cB instanceof ChildA));

System.out.println(“cB instanceof Parent : " + (cB instanceof Parent));

System.out.println("cG instanceof ChildA: " + (cG instanceof ChildA));

System.out.println("cG instanceof Parent: " + (cG instanceof Parent));

> p instanceof Parent: true > p instanceof ChildA: false > cA instanceof Parent: true > cA instanceof ChildA: true > //compile error, cannot be converted

> cB instanceof Parent : true

> cG instanceof ChildA: true > cG instanceof Parent : true

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Example

> Child A 40 >

castP = new ChildA();

System.out.println(castP.toString());

if(castP instanceof GrandChildA) { gC = (GrandChildA)castP; System.out.println(gC.toString()); System.out.println(gC.methodA()); System.out.println(gC.methodGrand()); } } }

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Benefits and Downsides

Flexibility

–

Model Object

Heterogeneous Collection

Polymorphic Arguments

Run-time exception

–

ClassCastException

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Heterogeneous Collection

Collections of objects with different class types

public static void main(String args[]){ Parent listP[] = new Parent[4];

listP[0] = new ChildB(); listP[1] = new ChildA(); listP[2] = new Parent();

listP[3] = new GrandChildA(); }

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Example

> 0 Child B 30 > method Child B > 1 Child A 20 > method Child A > 2 Parent 10 > 3 Grand Child 40 > method Child A

> method Grand Child A

for(int i = 0; i < 4; i++){

System.out.println(i+" "+listP[i].toString());

if(listP[i] instanceof ChildA) { ChildA cA = (ChildA)listP[i]; System.out.println(cA.methodA());

}

if(listP[i] instanceof ChildB) { ChildB cB = (ChildB)listP[i]; System.out.println(cB.methodB());

}

if(listP[i] instanceof GrandChildA) {

GrandChildA gC = (GrandChildA)listP[i]; System.out.println(gC.methodGrand());

}

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Polymorphic Arguments/ Subtype

Polymorphism

Polymorphic arguments adalah tipe data suatu

argumen pada suatu method yang bisa menerima

suatu nilai yang bertipe subclass-nya.

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Polymorphic Arguments/ Subtype

Polymorphism

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Polymorphic Arguments/ Subtype

Polymorphism

class Pegawai {

…

}

class Manajer extends Pegawai {

…

}

public class Tes {

public static void Proses(Pegawai peg) {

…

}

public static void main(String args[]) {

Manajer man = new Manajer();

Proses(man);

}

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Exercise

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Exercise - Detail

Shapes

- int numSides - String color + Shapes ()

+ Shapes (int numSides, String color) + int getNumSides() + String getColor() + double getArea() + double getPerimeter() + String getDetail() <<interface>> Resizable

+ resize (double zoom)

Rectangle - double height - double width

+ Rectangle (double height, double width)

+ Rectangle (int numSides, String color, double height, double width) + double getArea()

+ double getPerimeter()

Triangle - double base

- double height

+ Triangle(int base, int height)

+ Triangle (int numSides, String color, double base, double height)

+ double getEdgeLength() + double getArea()

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Buat implementasi class diagram tersebut dalam

bahasa Java! (Asumsi: segitiga yang dimaksud

pada kelas Triangle adalah segitiga sama kaki)

Buat driver dengan skenario:

–

Instansiasi object dari class Rectangle dan Triangle.

–

Masukkan object-object di atas ke ArrayList dari Shape.

–

Lakukan iterasi Shape dalam ArrayList. Jika Shape bisa

di-resizable, maka lakukan resize 0,5 kali. Kemudian

tampilkan perimeter dan area untuk setiap Shape yang

ada di ArrayList.

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