Problem

You work at a video game company as a junior programmer and have been tasked with writing a program, in Java, to calculate the angle of the hands on a clock. This program will be used in an upcoming game that features a time limit on certain tasks. In order to test your program, you will prompt the "user" for the hour and minute count. Then, assuming 12:00 is at position 0, calculate and output the angle of both the hour and minute hand. In order to make the visual designer's job easier, your solution will have to return the hour hand to the 0 degree position at 12:00.

Here’s an example run of the program, using 9:29 as the time.

Hour: 9
Minute: 29
The hour hand is at 284.5 degrees and the minute hand is at 174.0 degrees.
Programmed by [put your name here]
*** End of Processing ***

Creating this program will require a number of steps:

• Figure out how far the hour and minute hands travel every minute.
• Create the formulas.
• Figure out how to return 0 degrees for the hour hand at 12:00.

Part of the specifications requires the input and output to be echoed to System.out.

Hands

Solution

There are three steps to solving this question.

Calculate How Fast the Hands Travel

We first need to calculate how far the hour and minute hands travel each minute. The Minute Hand is easier, so we will start with it.

The Minute Hand

The Minute Hand travels 90 degrees in 15 minutes, which gives:

90 degrees/15 minutes = 6 degrees/minute

The Hour Hand

The Hour Hand is a bit trickier. It travels the full 360 degrees in 12 hours, which gives us:

360 degrees/12 hours = 30 degrees every hour or 1 degree every 2 minutes

Create the Formulas

Now we need to take the above information and create formulas we can use in our coding solution.

The Minute Hand

minuteDegree = minute * 6;

The Hour Hand

This solution requires both aspects of our calculations above: the fact that in one hour, the Hour Hand moves 30 degrees; and the fact that the Hour Hand moves one degree every two minutes.

hourDegree = (hour * 30) + (minute*0.5);

Resetting the Hour Hand at 12:00

However, when hour is 12, the hourDegree will be 360 degrees or greater using the above solution. We need to add a way to reset the degree count back to 0. An easy way to do this is to use modulus.

hourDegree = ((hour * 30) + (minute*0.5)) % 360;

This is just one way to calculate the hourDegree. Another way would be to calculate hour % 12 so the hour value is reset to 0.

Code

Solution Code

import javax.swing.*;
import java.util.Date;

/**
 * Calculate the angles of the Hour and Minute Hands based on the current time
 *
 * @author:     1010 Instructors
 * @version:    2011-April
 */

public class CaseStudy2_Hands_Solution 
{
    /**
     * PURPOSE: given an hour and minute count, calculate the angles of the hands
     */
    public static void main (String [] args) 
    {

        //variables declared here
        int hour, minute; // the hour and minute counts. If the time is 3:16, hour will be 3 and minute will be 16.
        double hourDegree, minuteDegree; // the angles of the hour and minute hands
        String input; // this is used with showInputDialog to get the input from the user

        // initialize variables
        hour = 0;
        minute = 0;
        hourDegree = 0;
        minuteDegree = 0;
        input = "";

        //get hour and echo to System.out
        input = JOptionPane.showInputDialog("What is the hour?");
    	hour = Integer.parseInt(input);
    	System.out.println("Hour: " + hour);

        //get minute and echo to System.out
    	input = JOptionPane.showInputDialog("What is the minute?");
    	minute = Integer.parseInt(input);
    	System.out.println("Minute: " + minute);

        //calculate the minuteDegree
        minuteDegree = minute * 6;

        //calculate the hourDegree
        hourDegree = ((hour * 30) + (minute*0.5)) % 360;

        //output
    	System.out.println("The hour hand is at " + hourDegree + " degrees \nand the minute hand is at " + minuteDegree + " degrees.");

        System.out.println("\nProgrammed by COMP 1010 Instructors");
        System.out.println("Date: " + new Date());
        System.out.println ("*** End of Processing ***");

    }//end main
}//end class