[JAVA] Design Pattern - Behaviour - Strategy

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[JAVA] Design Pattern - Behaviour - Strategy

system69

10-10-2014 16:18

[JAVA] Design Pattern - Behaviour - Strategy

Strategy Pattern menurut gue ibarat mesin bor yang mata bor nya bisa kita gonta ganti sesuai kebutuhan

Spoiler for Deskripsi Resmi:

Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
http://www.oodesign.com/strategy-pattern.html

Misal kita lagi buat program game RPG. Kita buat sebuah class CharacterObject sebagai Karakter yang mempunyai property name dan method attack().

Spoiler for Class CharaterObject:

Code:



public class CharacterObject {

 private String name="Player";

 public String getName() {

 return name;

 }

 public void setName(String name) {

 this.name = name;

 }

 // default karakter menyerang pake tangan kosong

 public void attack(){

 System.out.println("Gue gak punya senjata");

 System.out.println("Serang pake tangan");

 }

}

di dalam game yang kita buat akan ada Karakter tipe :
Wizard -> menyerang dengan sihir
Knight -> menyerang dengan pedang
Ranger -> menyerang dengan panah
Gunner -> menyerang dengan pistol
Assassin -> menyerang dengan pisau

tentunya kita akan buat kelas baru turunan dari class CharacterObject dengan meng-override method attack()

Spoiler for Class Wizard-Knight-Ranger-Gunner-Assasin:

Code:



public class Wizard extends CharacterObject {

 public Wizard(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

 //override method yang diturunkan CharacterObject

 public void attack() {

 System.out.println("Gue punya tongkat sihir");

 System.out.println("Serang pake sihir");

 }

}



public class Knight extends CharacterObject {

 public Knight(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

 //override method yang diturunkan CharacterObject

 public void attack() {

 System.out.println("Gue punya pedang");

 System.out.println("Serang pake pedang");

 }

}



public class Ranger extends CharacterObject {

 public Ranger(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

 //override method yang diturunkan CharacterObject

 public void attack() {

 System.out.println("Gue punya panah");

 System.out.println("Serang pake panah");

 }

}



public class Gunner extends CharacterObject {

 public Gunner(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

 //override method yang diturunkan CharacterObject

 public void attack() {

 System.out.println("Gue punya pistol");

 System.out.println("Serang pake pistol");

 }

}



public class Assassin extends CharacterObject {

 public Assassin (String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

 //override method yang diturunkan CharacterObject

 public void attack() {

 System.out.println("Gue punya pisau");

 System.out.println("Serang pake pisau");

 }

}

Kita buat program utamanya

Spoiler for Class Game:

Code:



public class Game 

{

 public static void main( String[] args )

 {

 CharacterObject wizard = new Wizard("Wizard");

 System.out.println("Job Class Player :" + wizard.getName());

 wizard.attack();

 CharacterObject knight = new Knight("Knight");

 System.out.println("Job Class Player :" + knight.getName());

 knight.attack();

 CharacterObject ranger = new Ranger("Ranger");

 System.out.println("Job Class Player :" + ranger.getName());

 ranger.attack();

 CharacterObject gunner = new Gunner("Gunner");

 System.out.println("Job Class Player :" + gunner.getName());

 gunner.attack();

 CharacterObject assassin = new Assassin("Assassin");

 System.out.println("Job Class Player :" + assassin.getName());

 assassin.attack();

 }

}

Output :

Code:



Job Class Player :Wizard

Gue punya tongkat sihir

Serang pake sihir

Job Class Player :Knight

Gue punya pedang

Serang pake pedang

Job Class Player :Ranger

Gue punya panah

Serang pake panah

Job Class Player :Gunner

Gue punya pistol

Serang pake pistol

Job Class Player :Assassin

Gue punya pisau

Serang pake pisau

Program game di atas selesai dibuat tapi ada beberapa permasalahan :

setiap job class player turunan CharacterObject pasti meng-override method attack. dan ketika kita akan menambahkan job class player baru maka kita harus meng-override method attack
bagaimana kalo setiap player bisa memakai senjata apa saja atau berganti job class?

Disinilah fungsi Strategy pattern berperan. Pertama kita buat interface untuk attack. Lalu kita buatkan class untuk masing2 senjata dengan mengimplementasikan interface attack tersebut

Spoiler for Refactoring:

Code:



public interface Attack {

 public void attack();

}



public class MagicWeapon implements Attack {

 public void attack() { 

 System.out.println("Gue punya tongkat sihir");

 System.out.println("Serang pake sihir");

 }

}



public class SwordWeapon implements Attack {

 public void attack() {

 System.out.println("Gue punya pedang");

 System.out.println("Serang pake pedang");

 }

}



public class GunWeapon implements Attack {

 public void attack() {

 System.out.println("Gue punya pistol");

 System.out.println("Serang pake pistol");

 }

}



public class BowWeapon implements Attack {

 public void attack() {

 System.out.println("Gue punya panah");

 System.out.println("Serang pake panah");

 }

}



public class KnifeWeapon implements Attack {

 public void attack() {

 System.out.println("Gue punya pisau");

 System.out.println("Serang pake pisau");

 }

}



public class DefaultWeapon implements Attack {

 // default karakter menyerang pake tangan kosong

 public void attack(){

 System.out.println("Gue gak punya senjata");

 System.out.println("Serang pake tangan");

 }

}

Kita lakukan sedikit perubahan pada class CharacterObject

Spoiler for Class CharacterObject baru:

Code:



public class CharacterObject {

 private String name="Player";

 private Attack weapon = new DefaultWeapon();

 public String getName() {

 return name;

 }

 public void setName(String name) {

 this.name = name;

 }

 public Attack getWeapon() {

 return weapon;

 }

 public void setWeapon(Attack weapon) {

 this.weapon = weapon;

 }

 // cukup panggil interface tanpa harus tau implementasi aslinya

 public void attack(){

 this.weapon.attack();

 }

}

Lalu kita lakukan perubahan pada job class yang kita buat. Perhatikan method attack() yang selalu di override hilang.

Spoiler for Refactor:

Code:



public class Wizard extends CharacterObject {

 public Wizard(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

}



public class Knight extends CharacterObject {

 public Knight(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

}



public class Ranger extends CharacterObject {

 public Ranger(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

}



public class Gunner extends CharacterObject {

 public Gunner(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

}



public class Assassin extends CharacterObject {

 public Assassin(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

}

kita coba jalankan di program utama

Spoiler for New Class Game:

Code:



public class Game

{

 public static void main( String[] args )

 {

 CharacterObject wizard = new Wizard("Wizard");

 wizard.setWeapon(new MagicWeapon());

 System.out.println("Job Class Player :" + wizard.getName());

 wizard.attack();

 System.out.println("Ganti senjata pake pedang");

 wizard.setWeapon(new SwordWeapon());

 wizard.attack();

 System.out.println("Ganti Senjata pake pistol");

 wizard.setWeapon(new GunWeapon());

 wizard.attack();

 }

}

Output :

Code:



Job Class Player :Wizard

Gue punya tongkat sihir

Serang pake sihir

Ganti senjata pake pedang

Gue punya pedang

Serang pake pedang

Ganti Senjata pake pistol

Gue punya pistol

Serang pake pistol

Kesimpulan :

kita bisa menghilangkan duplikasi override pada setiap job class

penambahan job class baru seperti Paladin tidak harus mengoverride method attack dan dapat menggunakan senjata apa saja

Code:



public class Paladin extends CharacterObject {

 public Paladin(String name){

 // property nama otomatis diturunkan dari CharacterObject

 this.setName(name);

 }

}

Dengan Strategy Pattern kita dapat membuat suatu fungsi yang bisa kita copot dan pasang pada suatu object.

Spoiler for Buat yang lebih pahamUML:

[JAVA] Design Pattern - Behaviour - Strategy

Silahkan di BOOKMARK (CTRL+D) gan buat referensi
Bisa diterapkan pake bahasa lain yang support OOP

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