将int转换为double Java

Question

I'm currently having an issue with my code. I have to declare hours and minutes as int, and totalTimeHours as double. totalTimeHours is used to store the total time in hours, ex 6.555 hrs. The problem I'm working on requires the answer to be found in hours and minutes, for example. 6 hours and 36 minutes. For my final run, I need to use 14.7 for gallons of gas used and 359.5 for distance. I used hours = (int)totalTimeHours to extract the whole number 6 and am supposed to find the remainder of time left over and multiply that by 60 to find minutes, but that's where I'm getting held up on.

Below is my code:

  public static void computeMilesPerGallon()
  {   //start brackett for computeMilesPerGallon

     double gallons, distance, mpg, totalTimeHours;   //totalTimeHours is the total  time in just hours
                                                                         //for example totalTimeHours = 6.5555 hrs
     int minutes, hours;
     final String DASHES = "-----------------------------------------------";
     final double AVERAGE_SPEED = 54.5;     

     DecimalFormat oneDecimalDigits = new DecimalFormat ("0.0");   //prints decimal to 1 places
     DecimalFormat threeDecimalDigits = new DecimalFormat ("0.000");   //prints decimal to 3 places  

     System.out.println ("\n\t\t\tSpeed Problem");
     System.out.println ("\t\t\t-------------");
     System.out.print ("\n\t\tEnter in the gallons of gas used: ");   //gets gallons of gas used
     gallons = scan.nextDouble();

     System.out.print ("\t\tEnter in the total distance driven: ");   //gets total distance driven
     distance = scan.nextDouble();

     mpg = distance / gallons;   //calculates mpg
     System.out.println ("\t\tThis is your miles per gallon (mpg): " + oneDecimalDigits.format(mpg));  
                                                                         //displays mpg
    //calculates time// 
     totalTimeHours = distance / AVERAGE_SPEED;

    //below line displays total time in hours to 3 decimal places
     System.out.println ("\n\t\tThis is was your time in hours: " 
                                        + threeDecimalDigits.format(totalTimeHours));

    //extracts hours from time in hours
     hours = (int)totalTimeHours;
        minutes = Math.round((totalTimeHours - hours) * 60);

    //prints total time in hrs and minutes
     System.out.println ("\t\tThis is the total time in hours and minutes: " + hours 
                                            + " hours and " + minutes + " minutes");  

     System.out.println ("\t" + DASHES);

  }

Answer 1

Replace :

minutes = Math.round((totalTimeHours - hours) * 60);

With :

minutes = Math.round((float)((totalTimeHours - hours) * 60));

or

minutes = (int)Math.round((totalTimeHours - hours) * 60);

There are two methods round in Math

long Math.round(double);
int Math.round(float);

You are passing in a double argument so you call the one that returnes a long and you assign it to an int ,thats wrong.

Answer 2

I didn't read all of your code, but that should help solve the problem you described in your text:

    double dTime = 6.555;
    int hours = (int) dTime;
    int minutes = (int) ((dTime - hours) * 60);
    System.out.println(hours + ":" + minutes); // prints 6:33