使用Java中的多种方法计算几何图形的面积

Question

My program will calculate the area but I need to have each different shape in it's own method and I'm having difficulty understanding how to first separate them all into their own method and link them all together. Any help is much appreciated.

import java.util.Scanner;
public class Project4 {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        String s = "Please choose which area/volume to calculate: 1-Circle 2-Triangle 3-Cone 4-Cylinder 5-Sphere 6-Quit: ";
        System.out.print(s);
        System.out.println(" ");
        int num = keyboard.nextInt();
        if (num < 1 || num > 6){
            System.out.print("Please choose a number between 1 and 6: ");
            num = keyboard.nextInt();
        }
        if(num == 1){
            System.out.print("Please enter the radius: ");
            double r = keyboard.nextDouble();
            double a;
            a = 3.14 * r * r;
            System.out.print("The area of the circle is: " + a);
            System.out.println(" ");
            System.out.print(s);
            num = keyboard.nextInt();
        }
        if(num == 2){
            System.out.print("Please enter the base: ");
            double b = keyboard.nextDouble();
            double at;
            System.out.print("Please enter the height: ");
            double h = keyboard.nextDouble();
            at = .5 * b * h;
            System.out.print("The area of the triangle is: " + at);
            System.out.println(" ");
            System.out.print(s);
            num = keyboard.nextInt();
        }
        if(num == 3){
            System.out.print("Please enter the radius: ");
            double r = keyboard.nextDouble();
            System.out.print("Please enter the height: ");
            double h = keyboard.nextDouble();
            double v1;
            v1 = (1/3) * 3.14 * r * r * h;
            System.out.print("The volume of the cone is: " + v1);
            System.out.println(" ");
            System.out.print(s);
            num = keyboard.nextInt();
        }
        if(num == 4){
            System.out.print("Please enter the radius: ");
            double r = keyboard.nextDouble();
            System.out.print("Please enter the height: ");
            double h = keyboard.nextDouble();
            double vc;
            vc = 3.14 * r * r * h;
            System.out.print("The volume of the cylinder is: " + vc);
            System.out.println(" ");
            System.out.print(s);
            num = keyboard.nextInt();
        }
        if(num == 5){
            System.out.print("Please enter the radius: ");
            double r = keyboard.nextDouble();
            double vs;
            vs = (4/3) * 3.14 * r * r * r;
            System.out.print("The volume of the sphere is: " + vs);
            System.out.println(" ");
            System.out.print(s);
            num = keyboard.nextInt();
        }
        if(num == 6){
            System.out.print("Thank you for using this program");
        }

}
}

Answer 1

You can use switch..case

switch(num) {
  case 1: calculateCircleArea();
          break;
  case 2: calculateTriangleArea();
          break;
  case 3: calculateConeVolume();
          break;
  case 4: calculateCylinderVolume();
          break;
  case 5: calculateSphereVolume();
          break;
  case 6: System.out.print("Thank you for using this program");
          break;
  default: System.out.print("Please choose a number between 1 and 6: ");
           break;
}

Answer 2

You can create new private/public methods to do the calculations and seperate them.

Take this part

if(num == 1){
    System.out.print("Please enter the radius: ");
    double r = keyboard.nextDouble();
    double a;
    a = 3.14 * r * r;
    System.out.print("The area of the circle is: " + a);
    System.out.println(" ");
    System.out.print(s);
    num = keyboard.nextInt();
}

You can create a new method for the calculation like so

public static double getArea(double radius)
{
return 3.14*radius*radius;
}

Then, inside your if statement you can say

if(num == 1){
        System.out.print("Please enter the radius: ");
        double r = keyboard.nextDouble();
        double a;
        a = getArea(r);
        System.out.print("The area of the circle is: " + a);
        System.out.println(" ");
        System.out.print(s);
        num = keyboard.nextInt();
    }

you see in this case, you get a one-line method which isn't very usefull. But you can split off more extensive calculations as well, this is just as an example. In addition, instead of all the if-blocks, you can use a switch statement like the other answer shows you.