Pola desain. Dekorator

Kita wis dideleng nggunakake obyek singleton, nanging sampeyan bisa uga durung éling sing strategi iki pola desain, lan salah siji sing paling digunakake ing.

Nyatane, ana akeh pola kasebut, lan bisa diklasifikasikake miturut tujuan tartamtu.

Klasifikasi pola

Biasane, pola ditondoi dening masalah sing ditanggulangi. Ayo goleki sawetara pola sing asring kita temoni nalika nggarap Jawa:

Ing Java.io, kelas ing ngisor iki ngetrapake pola:

Pola dekorator

Ayo bayangake yen kita nggambarake model kanggo desain omah.

Umumé, pendekatan katon kaya iki:

Kaping pisanan, kita duwe pilihan sawetara jinis omah. Konfigurasi minimal yaiku siji lantai kanthi atap. Banjur kita nggunakake kabeh jinis dekorator kanggo ngganti paramèter tambahan, sing kanthi alami mengaruhi rega omah.

Kita nggawe kelas House abstrak:

public abstract class House {
	String info;
 
	public String getInfo() {
    	return info;
	}
 
	public abstract int getPrice();
}
    

Ing kene kita duwe 2 cara:

• getInfo () ngasilake informasi babagan jeneng lan fitur omah kita;
• getPrice () ngasilake rega konfigurasi omah saiki.

Kita uga duwe implementasine House standar - bata lan kayu:

public class BrickHouse extends House {
 
	public BrickHouse() {
    	info = "Brick House";
	}
 
	@Override
	public int getPrice() {
    	return 20_000;
	}
}
 
public class WoodenHouse extends House {
 
	public WoodenHouse() {
    	info = "Wooden House";
	}
 
	@Override
	public int getPrice() {
    	return 25_000;
	}
}
    

Loro-lorone kelas kasebut marisi kelas House lan ngilangi cara regane, nyetel rega khusus kanggo omah standar. Kita nyetel jeneng ing konstruktor.

Sabanjure, kita kudu nulis kelas dekorator. Kelas iki uga bakal oleh warisan kelas House . Kanggo nindakake iki, kita nggawe kelas dekorator abstrak.

Ing kana kita bakal menehi logika tambahan kanggo ngganti obyek. Kaping pisanan, ora bakal ana logika tambahan lan kelas abstrak bakal kosong.

abstract class HouseDecorator extends House {
}
    

Sabanjure, kita nggawe implementasi dekorator. Kita bakal nggawe sawetara kelas sing ngidini kita nambah fitur tambahan ing omah:

public class SecondFloor extends HouseDecorator {
	House house;
 
	public SecondFloor(House house) {
    	this.house = house;
	}
 
	@Override
	public int getPrice() {
    	return house.getPrice() + 20_000;
	}
 
	@Override
	public String getInfo() {
    	return house.getInfo() + " + second floor";
	}
}
    

Konstruktor dekorator nampa omah sing bakal "hiasan", yaiku nambah modifikasi. Lan kita ngalahake cara getPrice () lan getInfo () , bali informasi babagan omah anyar dianyari adhedhasar lawas.

public class Garage extends HouseDecorator {
 
	House house;
	public Garage(House house) {
    	this.house = house;
	}
 
	@Override
	public int getPrice() {
    	return house.getPrice() + 5_000;
	}
 
	@Override
	public String getInfo() {
    	return house.getInfo() + " + garage";
	}
}
    

Saiki kita bisa nganyari omah kita karo dekorator. Kanggo nindakake iki, kita kudu nggawe omah:

House brickHouse = new BrickHouse();
    

Sabanjure, kita nyetel kitaomahvariabel padha karo dekorator anyar, ngliwati omah kita:

brickHouse = new SecondFloor(brickHouse); 
    

kitaomahvariabel saiki dadi omah kanthi lantai loro.

Ayo goleki kasus panggunaan sing nglibatake dekorator:

House brickHouse = new BrickHouse(); 

  System.out.println(brickHouse.getInfo());
  System.out.println(brickHouse.getPrice());
                    

House brickHouse = new BrickHouse(); 

  brickHouse = new SecondFloor(brickHouse); 

  System.out.println(brickHouse.getInfo());
  System.out.println(brickHouse.getPrice());
                    

House brickHouse = new BrickHouse();
 

  brickHouse = new SecondFloor(brickHouse);
  brickHouse = new Garage(brickHouse);

  System.out.println(brickHouse.getInfo());
  System.out.println(brickHouse.getPrice());
                    

House woodenHouse = new SecondFloor(new Garage(new WoodenHouse())); 

  System.out.println(woodenHouse.getInfo());
  System.out.println(woodenHouse.getPrice());
                    

House woodenHouse = new WoodenHouse(); 

  House woodenHouseWithGarage = new Garage(woodenHouse);

  System.out.println(woodenHouse.getInfo());
  System.out.println(woodenHouse.getPrice());

  System.out.println(woodenHouseWithGarage.getInfo());
  System.out.println(woodenHouseWithGarage.getPrice());
                    

Conto iki nggambarake keuntungan kanggo nganyarke obyek kanthi dekorator. Dadi kita ora nggantiomah kayuobyek dhewe, nanging nggawe obyek anyar adhedhasar lawas. Kene kita bisa ndeleng sing kaluwihan teka karo cacat: kita nggawe obyek anyar ing memori saben wektu, nambah konsumsi memori.

Deleng diagram UML program kita:

A decorator duwe implementasine super prasaja lan mbosenke ngganti obyek, nganyarke mau. Dekorator bisa dikenali dening konstruktor sing, kang njupuk minangka obyek paramèter saka jinis abstrak padha utawa antarmuka minangka kelas saiki. Ing Jawa, pola iki akeh digunakake ing kelas I/O.

Contone, kaya sing wis dingerteni, kabeh subkelas java.io.InputStream , OutputStream , Reader lan Writer duwe konstruktor sing nampa obyek saka kelas sing padha.