Java 디자인 패턴-02.Factory Method

(Java 디자인 패턴 스터디 모집 중 : https://github.com/bluedskim/javaDesignPatterns)

Factory design Pattern in Java – with examples

(출처:Abstract Factory Design Pattern in C#)

해결하려는 문제

  1. 생성자를 직접 호출해서 객체를 생성하는 경우 해당 객체와 클라이언트가 강하게 결합되게 되어 확정성이 떨어진다.

개요

  • 생성자를 호출하지 않고 생성하기 위한 패턴(생성될 클래스를 지정하지 않는다)
  • 해당 클래스를 사용하는 클래스에 하드코딩을 없앨 수 있다.

클래스 다이어그램

Factory Method 패턴(김동석)

소스

  • Shape.java : 도형(인터페이스) 
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    package net.dskim.desingpattern.factorymethod;

public interface Shape {
	String draw();
}
  • 도형 객체들 : Shape.java 를 implement
    • Rectangle.java : 사각형 
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      package net.dskim.desingpattern.factorymethod;

public class Rectangle implements Shape {
	@Override
	public String draw() {
		return "draw Rectangle";
	}
}
    • Circle.java : 원 
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      package net.dskim.desingpattern.factorymethod;

public class Circle implements Shape {
	@Override
	public String draw() {
		return "draw Circle";
	}
}
    • Square.java : 정사각형 
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      package net.dskim.desingpattern.factorymethod;

public class Square implements Shape {
	@Override
	public String draw() {
		return "draw Square";
	}
}
  • ShapeFactory.java : 도형 팩토리(Virtual Constructor) 
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    package net.dskim.desingpattern.factorymethod;

public class ShapeFactory {
	// use getShape method to get object of type shape
	public Shape getShape(String shapeType) {
		if (shapeType == null) {
			return null;
		}
		if (shapeType.equalsIgnoreCase("CIRCLE")) {
			return new Circle();

		} else if (shapeType.equalsIgnoreCase("RECTANGLE")) {
			return new Rectangle();

		} else if (shapeType.equalsIgnoreCase("SQUARE")) {
			return new Square();
		}

		return null;
	}
}
  • 클라이언트 : FactoryMethodTest.java 
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    package net.dskim.desingpattern.factorymethod;

import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.Test;
import lombok.extern.slf4j.Slf4j;

@Slf4j
public class FactoryMethodTest {
	@Test
	public void decoratorTest() {
		ShapeFactory shapeFactory = new ShapeFactory();

		// get an object of Circle and call its draw method.
		Shape shape1 = shapeFactory.getShape("CIRCLE");

		// call draw method of Circle
		String drawResult = shape1.draw();
		log.info("className={}, drawResult={}", shape1.getClass().getSimpleName(), drawResult);
		assertEquals("draw Circle", drawResult);

		// get an object of Rectangle and call its draw method.
		Shape shape2 = shapeFactory.getShape("RECTANGLE");

		// call draw method of Rectangle
		drawResult = shape2.draw();
		log.info("className={}, drawResult={}", shape2.getClass().getSimpleName(), drawResult);
		assertEquals("draw Rectangle", drawResult);

		// get an object of Square and call its draw method.
		Shape shape3 = shapeFactory.getShape("SQUARE");

		// call draw method of square
		drawResult = shape3.draw();
		log.info("className={}, drawResult={}", shape3.getClass().getSimpleName(), drawResult);
		assertEquals("draw Square", drawResult);
	}
}

참고