創建一個抽象類來獲取周邊和區域？

我給出的問題：創建一個抽象類來獲取周邊和區域？

編寫一個封裝形狀的抽象超類：一個形狀有兩個抽象方法：一個返回形狀的周邊，另一個返回鞋的區域。它也有一個名爲PI的常量字段。這個類有兩個非抽象的子類：一個封裝一個圓，另一個封裝一個矩形。圓有一個額外的屬性，其半徑。矩形有兩個額外的屬性，其寬度和高度。您還需要包含一個客戶端類來測試這兩個類。

下面是我所做的工作：

Shape.java

public abstract class Shape 
{ 

public abstract double getPerimeter(); 
public abstract double getArea(); 

}

Circle.java

public class Circle extends Shape 
{ 
private double radius; 
final double pi = Math.PI; 

//Defualt Constructor, calls Shape default constructor 
public Circle() 
{ 
    //Set default value to radius 
    this.radius = 1; 
} 

public Circle(double radius) 
{ 
    this.radius = radius; 
} 

public double getArea() 
{ 
    //Return πr^2 (area formula) 
    //Use Math.pow method (page 141) in order to calculate exponent 
    return (pi * Math.pow(radius, 2)); 
} 

public double getPerimeter() 
{ 
    //Return 2πr (perimeter formula) 
    return (2 * pi * radius); 
}}

Rectangle.java

public class Rectangle extends Shape 
{ 
private double width, height; 
public Rectangle() 
{ 
    //set default value to width and height 
    this.width = 1; 
    this.height = 1; 
} 
public Rectangle(double width, double height) 
{ 
    this.width = width; 
    this.height = height; 
} 

public double getArea() 
{ 
    return width * height; 
} 

public double getPerimeter() 
{ 
    return 2 * (width + height); 
}}

ShapeClient.java

public class ShapeClient { 
public static void main(String [] args) 
{ 

    // To test Rectangle... 
    double width = 13, length = 9; 
    Shape rectangle = new Rectangle(width, length); 
    System.out.println("The rectangle width is: " + width 
      + " and the length is: " + length 
      + "The area is: " + rectangle.getArea() 
      + "and the perimeter is: " + rectangle.getPerimeter() + "."); 

    //To test Circle... 
    double radius = 3; 
    Shape circle = new Circle(radius); 
    System.out.println("The radius of the circle is: " + radius 
     + "The area is: " + circle.getArea() 
     + "and the perimeter is: " + circle.getPerimeter() + "."); 


}}

我的問題是：PI的常量字段是否需要在Shape類而不是Circle類中？如果是這樣，我應該如何將它從圈子類中取出，我應該如何將它放置在Shape類中？

來源

2017-05-02 user7124275

如果需要，您可以在Abstract類中使public static final int PI = 3.17。正如你應該在你的父類中聲明所有的常量一樣。但是它的公正學校項目和你永遠不會聲明更多使用PI值的形狀。 –