[JAVA/수업 과제 practice] 다형성 Lv. 1~2

✅ 답안과 비교하여 스스로 코드 개선점 짚어보기 완료(2022.01.09)

 

BASIC1. 사각형과 원의 면적, 둘레 구하기(클래스) ✅

Rectangle 면적 : 1473.15
Rectangle 둘레 : 154.4
Circle 면적 : 754.7676350249478
Circle 둘레 : 97.38937226128358

 

Application.class

객체 생성한 뒤 메소드 호출하는 방법보다 new 연산자 사용해 호출하는 것이 간단할 수 있다. 특히 이 경우는 한 번뿐인 호출이기 때문에 그렇다.

package com.greedy.level01.basic.polymorphism;

public class Application {

	public static void main(String[] args) {

//		ShapeManager shapeManager = new ShapeManager();
//		shapeManager.calcShape();
		new ShapeManager().calcShape();

	}

}

 

Circle.class

package com.greedy.level01.basic.polymorphism;

public class Circle extends Shape {
	
	public static double PI = Math.PI;
	private double radius; //반지름
	
	/* 기본 생성자 */
	public Circle() {}
	/* 매개변수 있는 생성자 */
	public Circle(double radius) {
		this.radius = radius;
	}
	
	public static double getPI() {
		return PI;
	}
	public static void setPI(double pI) {
		PI = pI;
	}
	public double getRadius() {
		return radius;
	}
	public void setRadius(double radius) {
		this.radius = radius;
	}
	
	/* 추상메소드 오버라이딩 */
	/* 원의 면적과 둘레 계산 */
	@Override
	public double area() {
		return PI * radius * radius;
	}
	@Override
	public double perimeter() {
		return 2 * radius * PI;
	}
	
	

}

 

Rectangle.class

package com.greedy.level01.basic.polymorphism;

public class Rectangle extends Shape {
	
	private double width;
	private double height;
	
	/* 기본 생성자 */
	public Rectangle() {}
	/* 매개변수 있는 생성자 */
	public Rectangle(double width, double height) {
		this.width = width;
		this.height = height;
	}
	
	public double getWidth() {
		return width;
	}
	public void setWidth(double width) {
		this.width = width;
	}
	public double getHeight() {
		return height;
	}
	public void setHeight(double height) {
		this.height = height;
	}
	
	/* 추상메소드 오버라이딩 */
	/* 사각형의 면적과 둘레 계산 */
	@Override
	public double area() {
		return width * height;
	}
	@Override
	public double perimeter() {
		return (width + height) * 2;
	}
	
}

 

Shape.class *abstract*

추상클래스와 추상메소드 선언 시에 클래스명 앞에도 abstract 키워드를 기억하자.

package com.greedy.level01.basic.polymorphism;

public abstract class Shape {
	/* 추상클래스와 추상메소드 선언 */
	public abstract double area();
	public abstract double perimeter();
	

}

 

ShapeManager.class

객체배열 크기는 문제상에 주어지지 않았다. 때문에 초기화를 바로 진행하는 것이 적합하다.

 

대상이 Rectangle과 Circle 둘 뿐이므로 삼항연산자를 사용할 수 있겠다.

String shapeType = s instance of Rectangle ? Rectangle : Circle;

package com.greedy.level01.basic.polymorphism;

public class ShapeManager {
	
	public void calcShape() {
		
		/* Shape 객체 배열 */
		Shape[] shape = {new Rectangle(34.5, 42.7), new Circle(15.5)};
		
		/* 면적과 둘레 출력 */
		for(Shape s : shape) {
			if(s instanceof Rectangle) {
				System.out.println("Rectangle 면적 : " + s.area());
				System.out.println("Rectangle 둘레 : " + s.perimeter());
			} else if(s instanceof Circle) {				
				System.out.println("Circle 면적 : " + s.area());
				System.out.println("Circle 둘레 : " + s.perimeter());
			}
		}
	}
}

 

---

 

NORMAL1-1. 사각형과 원의 면적, 둘레 구하기(인터페이스) ✅

Rectangle 면적 : 1473.15
Rectangle 둘레 : 154.4
Circle 면적 : 754.7676350249478
Circle 둘레 : 97.38937226128358

 

NORMAL1-2. 다운캐스팅 적용하여 삼각형 빗변 구하기 ✅

Circle - 면적 : 475.2915525615999, 둘레 : 77.28317927830892
Rectangle - 면적 : 1486.5600000000002, 둘레 : 156.4
Rectangle - 면적 : 568.56, 둘레 : 98.6
Triangle 면적 : 321.63, 둘레 : 82.39724906848504, 빗변 : 30.897249068485042
Triangle 면적 : 1608.32, 둘레 : 215.49977777750343, 빗변 : 89.99977777750343

 

Application.class

여기서도 객체 선언하지 않고 바로 new ShapeManager().calcShapeArray();로 쓸 수 있겠다.

package com.reminder.polymorphism_practice.interfaceimplements;

public class Application {

	public static void main(String[] args) {
		ShapeManager shapeManager = new ShapeManager();
		/* Part 1. Interface */
		shapeManager.calcShape();
		/* Part 2. Down-casting */
		shapeManager.calcShapeArray();

	}

}

 

IShape.interface

package com.reminder.polymorphism_practice.interfaceimplements;

public interface IShape {
	
	public abstract double area();
	public abstract double perimeter();

}

 

Circle.class

package com.reminder.polymorphism_practice.interfaceimplements;

public class Circle implements IShape {
	
	public static double PI = Math.PI;
	private double radius;
	
	public Circle() {}
	public Circle(double radius) {
		this.radius = radius;
	}
	
	public void setRadius(double radius) {
		this.radius = radius;
	}
	public double getRadius() {
		return radius;
	}
	
	@Override
	public double area() {
		return PI * radius * radius;
	}
	@Override
	public double perimeter() {
		return 2 * radius * PI;
	}

}

 

Rectangle.class

package com.reminder.polymorphism_practice.interfaceimplements;

public class Rectangle implements IShape {
	
	private double width;
	private double height;
	
	public Rectangle() {}
	public Rectangle(double width, double height) {
		this.width = width;
		this.height = height;
	}
	
	public void setWidth(double width) {
		this.width = width;
	}
	public void setHeight(double height) {
		this.height = height;
	}
	public double getWidth() {
		return width;
	}
	public double getHeight() {
		return height;
	}
	
	@Override
	public double area() {
		return width * height;
	}
	@Override
	public double perimeter() {
		return (width + height) * 2;
	}

}

 

ShapeManager.class

package com.reminder.polymorphism_practice.interfaceimplements;

public class ShapeManager {
	
	public void calcShape() {
		IShape[] iShape = {new Rectangle(34.5, 42.7), new Circle(15.5)};
//		Rectangle rect = new Rectangle();
//		Circle circ = new Circle();
		
		for(IShape s : iShape) {
			if(s instanceof Rectangle) {
				System.out.println("Rectangle 면적 : " + s.area());
				System.out.println("Rectangle 둘레 : " + s.perimeter());
			} else if(s instanceof Circle) {
				System.out.println("Circle 면적 : " + s.area());
				System.out.println("Circle 둘레 : " + s.perimeter());
			}
		}
	}
	
	public void calcShapeArray() {
		IShape[] iarr = new IShape[5];
		iarr[0] = new Circle(12.3);
		iarr[1] = new Rectangle(32.6, 45.6);
		iarr[2] = new Rectangle(18.4, 30.9);
		iarr[3] = new Triangle(30.2, 21.3);
		iarr[4] = new Triangle(89.6, 35.9);
		
		for(IShape p : iarr) {
			if(p instanceof Rectangle) {
				System.out.println("Rectangle - 면적 : " + p.area() + ", 둘레 : " + p.perimeter());
			} else if(p instanceof Circle) {
				System.out.println("Circle - 면적 : " + p.area() + ", 둘레 : " + p.perimeter());
			} else if(p instanceof Triangle) {
				System.out.println("Triangle 면적 : " + p.area() + ", 둘레 : " + p.perimeter() + ", 빗변 : " + ((Triangle)p).hypotenuse());
			}
		}
	}

}

 

Triangle.class

package com.reminder.polymorphism_practice.interfaceimplements;

public class Triangle implements IShape {
	
	private double base;
	private double height;
	
	public Triangle() {}
	public Triangle(double base, double height) {
		this.base = base;
		this.height = height;
	}
	
	public void setBase(double base) {
		this.base = base;
	}
	public void setHeight(double height) {
		this.height = height;
	}
	public double getBase() {
		return base;
	}
	public double getHeight() {
		return height;
	}

	@Override
	public double area() {
		return (base * height) / 2;
	}

	@Override
	public double perimeter() {
		return base + height + hypotenuse();
	}
	
	public double hypotenuse() {
		return Math.sqrt(base * base + height + height);
	}

}