How to round time to the nearest quarter hour in java?

Question

Given today\'s time e.g. 2:24PM, how do I get it to round to 2:30PM?

Similarly if the time was 2:17PM, how do I get it to round to 2:15PM?

Answer 1

A commented implementation for Java 8. Accepts arbitrary rounding units and increments:

 public static ZonedDateTime round(ZonedDateTime input, TemporalField roundTo, int roundIncrement) {
    /* Extract the field being rounded. */
    int field = input.get(roundTo);

    /* Distance from previous floor. */
    int r = field % roundIncrement;

    /* Find floor and ceiling. Truncate values to base unit of field. */
    ZonedDateTime ceiling = 
        input.plus(roundIncrement - r, roundTo.getBaseUnit())
        .truncatedTo(roundTo.getBaseUnit());

    ZonedDateTime floor = 
        input.plus(-r, roundTo.getBaseUnit())
        .truncatedTo(roundTo.getBaseUnit());

    /*
     * Do a half-up rounding.
     * 
     * If (input - floor) < (ceiling - input) 
     * (i.e. floor is closer to input than ceiling)
     *  then return floor, otherwise return ceiling.
     */
    return Duration.between(floor, input).compareTo(Duration.between(input, ceiling)) < 0 ? floor : ceiling;
  }

Source: myself