Java Programming Exercises: Calculations and Conversions

Exercise Listing 2.1: Calculate Circle Area

Write a simple application that computes the area of a circle, knowing that π = 3.14159 and radius = 20.

ComputeArea.java

public class ComputeArea {
    public static void main(String[] args) {
        double radius; // Declare radius
        double area; // Declare area
        // Assign a radius
        radius = 20; // radius is now 20
        // Compute area
        area = radius * radius * 3.14159;
        // Display results
        System.out.println("The area for the circle of radius " +
            radius + " is " + area);
    }
}

Exercise Listing 2.2: Calculate Circle Area with User Input

Write a Java program that calculates the area of the circle where the radius size is to be given by the user and π = 3.14159.

ComputeAreaWithConsoleInput.java

import java.util.Scanner; // Scanner is in the java.util package

public class ComputeAreaWithConsoleInput {
    public static void main(String[] args) {
        // Create a Scanner object
        Scanner input = new Scanner(System.in);
        // Prompt the user to enter a radius
        System.out.print("Enter a number for radius: ");
        double radius = input.nextDouble();
        // Compute area
        double area = radius * radius * 3.14159;
        // Display results
        System.out.println("The area for the circle of radius " +
            radius + " is " + area);
    }
}

Exercise Listing 2.3: Calculate Average of Three Numbers

Write a Java program that takes 3 numbers as input, calculates their average, and then prints the average on the screen.

ComputeAverage.java

import java.util.Scanner; // Scanner is in the java.util package

public class ComputeAverage {
    public static void main(String[] args) {
        // Create a Scanner object
        Scanner input = new Scanner(System.in);
        // Prompt the user to enter three numbers
        System.out.print("Enter three numbers: ");
        double number1 = input.nextDouble();
        double number2 = input.nextDouble();
        double number3 = input.nextDouble();
        // Compute average
        double average = (number1 + number2 + number3) / 3;
        // Display results
        System.out.println("The average of " + number1 + " " +
            number2 + " " + number3 + " is " + average);
    }
}

Exercise Listing 2.4: Convert Seconds to Minutes and Seconds

Write a program that obtains minutes and remaining seconds from an amount of time in seconds. For example, 500 seconds contains 8 minutes and 20 seconds.

DisplayTime.java

import java.util.Scanner;

public class DisplayTime {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter an integer for seconds: ");
        int seconds = input.nextInt();
        int minutes = seconds / 60;
        int remainingSeconds = seconds % 60;
        System.out.println(seconds + " seconds is " + minutes +
            " minutes and " + remainingSeconds + " seconds");
    }
}

Exercise Listing 2.5: Convert Fahrenheit to Celsius

Write a program that converts a Fahrenheit degree to Celsius using the formula celsius = (5/9)(fahrenheit – 32).

FahrenheitToCelsius.java

import java.util.Scanner;

public class FahrenheitToCelsius {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a degree in Fahrenheit: ");
        double fahrenheit = input.nextDouble();
        // Convert Fahrenheit to Celsius
        double celsius = (5.0 / 9) * (fahrenheit - 32);
        System.out.println("Fahrenheit " + fahrenheit + " is " +
            celsius + " in Celsius");
    }
}

Programming Exercise 2.4: Convert Pounds to Kilograms

Write a program that converts pounds into kilograms. The program prompts the user to enter a number in pounds, converts it to kilograms, and displays the result. One pound is 0.454 kilograms.

Exercise_02_04.java

import java.util.Scanner;

public class Exercise_02_04 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        final double KILOGRAMS_PER_POUND = 0.454; // Declare constant
        System.out.print("Enter a number in pounds: ");
        double pounds = input.nextDouble();
        double kilograms = pounds * KILOGRAMS_PER_POUND;
        System.out.println(pounds + " pounds is " + kilograms + " kilograms");
    }
}