Intro Java Assignment - Unit 9: Compiling/Running from Command Line

Question

Here is my question

• Write a Java class definition called FrustumContainer which describes a lab container shaped like the frustum of a cone, and computes the amount of liquid that each container will hold.

• Define a constructor for this class and include accessor methods for the container number, height, radius 1 of the container and radius 2 of the container, and a method to compute the amount of liquid (in litres) that the container can hold.

• Also include another class, called ContainerTester, which has a main method to test all methods of the FrustumContainer class.

• Compile both classes and execute the tester class using the command line environment.

Just wondering how to go about this, do the two classes have to go in separate files? I don't understand how ContainerTester can test all methods in FrustrumContainer

Here is my code so far:

import java.math.*;
import java.util.Scanner;
public class FrustrumContainer {
    Scanner in = new Scanner(System.in);
    double num = 0;
    double h = 0;
    double r1 = 0;
    double r2 = 0;
    double volume;`

public FrustrumContainer(double num, double h, double r1, double r2, double volume) {
    this.num = num;
    this.h = h;
    this.r1 = r1;
    this.r2 = r2;
    this.volume = volume;

public static double getNum() {
    num ++;
    return num;
}

public static double getHeight() {
    System.out.println("Enter height of container: ");
    h = in.next();
    return h;
}

public static double getR1() {
    System.out.println("Enter bottom radius: ");
    r1 = in.next();
    return r1;
}

public static double getR2(){
    System.out.println("Enter top radius: ");
    r2 = in.next();
    return r2;
}

public static double computeLiquid()


}
}

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


        }
    }
}

Answer 1

You should store them both in two separate classes and you then can test FrustrumContainer by calling the methods using syntax like

ClassName.methodName();

Because every method in FrustrumContainer is static you don't need to instantiate an FrustrumContainer object, you are calling the method directly from the class instead. You can call like this:

public static void main(String[] args) {
    FrustrumContainer.getNum();// note this only returns the number

    double num1 = FrustrumContainer.getNum();//you can store the returned type i.e double for num

    System.out.println(num1);//and print it to the console
}

Answer 2

You should have two classes,FrustumContainer.class and ContainerTester.class,and put both in the same dictionary.

FrustumContainer.class:

import java.util.Scanner;

public class FrustumContainer {
    int num = 0;
    double height = 0;
    double radius1 = 0;
    double radius2 = 0;
    double volume = 0;

    final static double PI = Math.PI;

    Scanner in = new Scanner(System.in);

    public FrustumContainer(){
        this.num ++;
    }

    public void getHeight(){
        System.out.println("please input the value of height (unit:dm):");
        height = in.nextDouble();
    }

    public void getRadius1(){
        System.out.println("please the input the value of radius1 (unit:dm):");
        radius1 = in.nextDouble();
    }

    public void getRadius2(){
        System.out.println("please the input the value of radius2 (unit:dm):");
        radius2 = in.nextDouble();
    }

    public double computeLiquid(){
        double height1 = 0;
        if(height <= 0 || radius1 <= 0 || radius2 <= 0){
            System.out.println("please input again");
        }else{
            if(radius1 < radius2) {
                // solve height1,(h1+h)/h1 = r2/r1
                height1 = height/(radius2/radius1 -1);
                // get volume, 1/3 * PI* (r2*r2*(h1+h) -r1*r1*h1)
                volume = (PI * ((radius2 * radius2 * (height1 + height)) - (radius1 * radius1 * height1)))/3;
            }else{
                height1 = height/(radius1/radius2 -1);
                volume = (PI * (radius1 * radius1 * (height1 + height)- radius2 * radius2 * height1))/3;
            }
        }
        return volume;
    }
}

ContainerTester.class:

public class ContainerTester {
        public static void main(String[] args){
            FrustumContainer frustumContainer = new FrustumContainer();
            frustumContainer.getHeight();
            frustumContainer.getRadius1();
            frustumContainer.getRadius2();
            int num = frustumContainer.num;
            double volume = frustumContainer.computeLiquid();
            System.out.println("The volume of NO."+ num +" container is " + volume + " L");
        }
    }

You can call the methods of FrustumContainer.class in ContainerTester.class like frustumContainer.getHeight() .