CS246 Teacher's Solution for 01 Teach - Circle Calculator

CircleCalculator.java

package byui.cs246.falin;

// This is sort of like #include in C++, except
// instead of importing the entire library file, it
// just tells the compiler exactly what we mean
// when we type the word "Scanner".
import java.util.Scanner;

public class CircleCalculator {

    // By marking this "static final" it acts like a constant.
    private static final Scanner _scanner = new Scanner( System.in );

    private double getRadius() {
        // Using print() instead of println() here, because we don't
        // want an end line.
        System.out.print("Enter the radius: ");

        // Read a double from the console input
        double radius = _scanner.nextDouble();
        return radius;
    }

    private void displayArea(double radius) {

        // The Java Math class contains many static method and constants
        // that are useful for mathematical calculations. See:
        // https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html
        double area = Math.PI * radius * radius;

        // Using format specifiers here to control
        // the output format. See:
        // https://docs.oracle.com/javase/tutorial/java/data/numberformat.html
        System.out.format("\tArea: %.2f\n", area);
    }

    private void displayCircumference(double radius) {

        double circ = Math.PI * radius * 2;
        System.out.format("\tCircumference: %.2f\n", circ);
    }


    public static void main(String[] args) {

        // In this case, we can't use the alternate syntax we mentioned
        // in the HelloWorld solution, because we need to keep a reference to
        // the instance in order to call the display methods.
        CircleCalculator calc = new CircleCalculator();

        double r = calc.getRadius();
        calc.displayArea(r);
        calc.displayCircumference(r);
    }
}