PracticalAstronomy_JDtoGD.java

public class HelloWorld
{
  public static void main(String[] args)
  {
    PracticalAstronomy astro = new PracticalAstronomy(2455002.25);
    double[] date = astro.getGregorianDay();
    System.out.print((int)date[0] + " " + (int)date[1] + " " + date[2]);
    //will output 2009 6 19.75
  }
}

// Public class Practical Astronomy
public class PracticalAstronomy
{
  private double jd;
  public PracticalAstronomy(double jd)
  {
   this.jd = jd; 
  }
  
  public double[] getGregorianDay()
  {
    jd = jd + 0.5;
    double I = (int)jd;
    double F = jd - I;
    double A = (int)((I - 1867216.25)/36524.25);
    double B = I > 2299160 ? I + A - (int)(A / 4) + 1 : I;
    double C = B + 1524;
    double D = (int)((C-122.1) / 365.25);
    double E = (int)(365.25 * D);
    double G = (int)((C-E)/30.6001);
    
    double d = C - E + F - (int)(30.6001 * G);
    double m = G < 13.5 ? G - 1 : G - 13;
    double y = m > 2.5 ? D - 4716 : D - 4715;
    
    return new double[] {y,m,d};
  }
    
}