Saturday, 17 July 2021

Find the angle between the hour and minute hands in Java

Find the angle between the hour and minute hands on an analog clock.

Given the time, calculate the smaller angle between the hour and minute hands on an analog clock in Java.

Java Program to find angle between hour and minute hand.

In 60 mins, clock minute hand takes 360 degree. so for 1 min = 360/60 = 6 degree.
In 12 hours, clock hour hand takes 360 degree. so for 1 hour = 360/12 = 30 degree 

But when it is 1.20, hour hand doesn't be on exact 1, and would be slightly crossed 1 (when it is 1.30, hour hand would be in between 1 and 2.) 
So we need to find out the exact position of the hour hand and the angle it covered, that is you need to find the angle hour hand makes for each minute passes. 

We already know 1 hour angle = 30 degree 
In 1 hour, we have 60 minutes, so in each minute, how much angle hour hand makes = 30/60 = 1/2.
 
package javabypatel.misc;

public class FindAngle {
    public static void main(String[] args) {
        System.out.println(findAngle(12, 25));
    }

   public static double findAngle(int hour, int minute) {
        // in 60 mins, it takes 360 degree. so for a 1 min = 360/60 = 6 degree
        double minAngle = minute * 6;

        // in 12 hours, it takes 360 degree. so for 1 hour = 360/12 = 30 degree
       double hourAngle = hour * 30;

        //but when it is 1.20, hour hand doesn't be on exact 1, and would be slightly crossed 1 (when it is 1.30, hour hand would be in between 1 and 2.)
        //So you need to find out the exact position of the hour hand and the angle it covered between a single hour.
        //that is you need to find the angle hour hand makes for each minute passes.
        //we already know 1 hour angle = 30 degree
        //In 1 hour, we have 60 minutes, so in each minute, how much angle hour hand makes = 30/60 = 1/2.
        double hourAngleForEachMinute = minute/2.0; //minute * 1/2; (divided by 2.0 to make it divide in double context)

        //Final hour angle would be hourAngle + hourAngleForEachMinute
        double finalHourAngle = hourAngle + hourAngleForEachMinute;

        double angle = Math.abs(finalHourAngle - minAngle);

        //analog clock is round, so clock hands make two angles, one in interior and one is exterior, Since we are told to return smaller angle we return minimum one.
        return Math.min(angle, 360-angle);
    }
}
at

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