学以致用——Java源码——使用多态输出平面及立体几何图形的面积和体积（Project: Shape Hierarchy）

程序功能：

使用继承和多态的面向编程思想，动态的判断几何形状，打印平面图形面积及立体几何图形的面积和体积。

这个习题让我从无到有创建了共10个类才完成，虽然简单，但是作为继承和多态的入门练习还是不错的！

测试结果：

逐个处理：

circle's area:201.06

square's area:64.00

triangle's area:24.00

sphere's area:804.25

sphere's volume:2144.66

cube's area:384.00

cube's volume:512.00

tetrahedron's area:110.85

tetrahedron's volume:60.34

多态处理：

图形 0是一个圆

面积：201.06

图形 1是一个正方形

面积：64.00

图形 2是一个三角形

面积：24.00

图形 3是一个球

面积：804.25

体积：2144.66

图形 4是一个立方体

面积：384.00

体积：512.00

图形 5是一个圆

面积：110.85

体积：60.34

代码：

1. 测试类

//Java How to Program, Exercise 10.13: Project: Shape Hierarchy
//by pandenghuang@163.com
/*** 10.13 (Project: Shape Hierarchy) Implement the Shape hierarchy shown in Fig.* 9.3. Each Two-DimensionalShape should contain method getArea to calculate the* area of the two-dimensional shape. Each ThreeDimensionalShape should have* methods getArea and getVolume to calculate the surface area and volume,* respectively, of the three-dimensional shape. Create a program that uses an* array of Shape references to objects of each concrete class in the hierarchy.* The program should print a text description of the object to which each array* element refers. Also, in the loop that processes all the shapes in the array,* determine whether each shape is a TwoDimensionalShape or a* ThreeDimensionalShape. If it’s a TwoDimensionalShape, display its area. If* it’s a ThreeDimensionalShape, display its area and volume.* * @author Pandenghuang@163.com* @Date Jan 7, 2019, 9:13:12 AM**/
public class ShapeHierarchyTest {public static void main(String[] args) {Circle circle = new Circle(8);Square square = new Square(8);Triangle triangle = new Triangle (6,8,10);Sphere sphere = new Sphere(8);Cube cube = new Cube(8);Tetrahedron tetrahedron = new Tetrahedron(8);System.out.printf("逐个处理：%n%n");System.out.printf("circle's area:%.2f%n", circle.getArea());System.out.printf("square's area:%.2f%n", square.getArea());System.out.printf("triangle's area:%.2f%n", triangle.getArea());System.out.printf("sphere's area:%.2f%n", sphere.getArea());System.out.printf("sphere's volume:%.2f%n", sphere.getVolume());System.out.printf("cube's area:%.2f%n", cube.getArea());System.out.printf("cube's volume:%.2f%n", cube.getVolume());System.out.printf("tetrahedron's area:%.2f%n", tetrahedron.getArea());System.out.printf("tetrahedron's volume:%.2f%n", tetrahedron.getVolume());Shape[] shapes = new Shape[6];shapes[0] = circle;shapes[1] = square;shapes[2] = triangle;shapes[3] = sphere;shapes[4] = cube;shapes[5] = tetrahedron;System.out.printf("%n%n多态处理：%n%n");// get type name of each object in employees arrayfor (int j = 0; j < shapes.length; j++) {String[] classInfo =shapes[j].getClass().getName().split("\\.");String className = classInfo[classInfo.length-1];String classNameCN = "圆";switch (className) {case "Circle":classNameCN = "圆";break;case "Square":classNameCN = "正方形";break;case "Triangle":classNameCN = "三角形";break;case "Sphere":classNameCN = "球";break;case "Cube":classNameCN = "立方体";break;case "Terahedron":classNameCN = "正四面体";break;}System.out.printf("图形 %d是一个%s%n", j, classNameCN); //打印对象的类型（类名）if (shapes[j] instanceof TwoDimensionalShape) System.out.printf("面积：%.2f%n%n", shapes[j].getArea());  //如果是二维图形，打印面积else if (shapes[j] instanceof ThreeDimensionalShape) {ThreeDimensionalShape threeDimensionalShape = (ThreeDimensionalShape)shapes[j];  //如果是三维图形，打印面积和体积System.out.printf("面积：%.2f%n", threeDimensionalShape.getArea());System.out.printf("体积：%.2f%n%n", threeDimensionalShape.getVolume());}}}}

2. 实体类

1）Shape类（基类，图形）

/*** * @author Pandenghuang@163.com* @Date Jan 7, 2019, 1:44:02 AM**/
public abstract class Shape {public abstract double getArea();
}

2）TwoDimensionalShape类（平面图形）

public abstract class TwoDimensionalShape extends Shape {}

3）ThreeDimensionalShape类（立体图形）

public abstract class ThreeDimensionalShape extends Shape{public abstract double getVolume(); }

4）Circle类（圆）

public class Circle extends TwoDimensionalShape {private double radius;Circle(double radius){this.radius = radius;}@Overridepublic double getArea() {return Math.PI*Math.pow(radius,2);}}

5）Square类（正方形）

public class Square extends TwoDimensionalShape{private double sideLength;Square(double sideLength){this.sideLength = sideLength;}@Overridepublic double getArea() {return Math.pow(sideLength,2);}
}

6）Triangle类（三角形）

public class Triangle extends TwoDimensionalShape {private double a;private double b;private double c;public Triangle (double a, double b, double c) {this.a = a;this.b = b;this.c = c;}@Overridepublic double getArea() {double p = (a + b + c)/2.0;return Math.sqrt(p*(p-a)*(p-b)*(p-c));}}

7) Sphere类（球）

public class Sphere extends ThreeDimensionalShape {private double radius;Sphere(double radius){this.radius = radius;}@Overridepublic double getArea() {return 4*Math.PI*Math.pow(radius,2);}@Overridepublic double getVolume() {return 4.0/3.0*Math.PI*Math.pow(radius,3);}
}

8）Cube类（立方体）

public class Cube extends ThreeDimensionalShape {private double length;Cube(double length){this.length = length;}@Overridepublic double getArea() {return 6*Math.pow(length,2);}@Overridepublic double getVolume() {return Math.pow(length,3);}
}

9）Tetrahedron类（正四面体）

public class Tetrahedron extends ThreeDimensionalShape {private double length;Tetrahedron(double length){this.length = length;}@Overridepublic double getArea() {return Math.sqrt(3)*Math.pow(length,2);}@Overridepublic double getVolume() {return Math.sqrt(2)/12*Math.pow(length,3);}
}