src/java.base/share/classes/java/time/Duration.java

*** 1348,1357 ****
--- 1348,1399 ----
       */
      public int toNanosPart(){
          return nanos;
      }
  
+ 
+     //-----------------------------------------------------------------------
+     /**
+      * Returns a copy of this {@code Duration} truncated to the specified unit.
+      * <p>
+      * Truncating the duration returns a copy of the original with fields
+      * smaller than the specified unit set to zero.
+      * For example, truncating with the {@link ChronoUnit#MINUTES MINUTES} unit will
+      * round down to the nearest minute, setting the seconds and nanoseconds to zero.
+      * <p>
+      * The unit must have a {@linkplain TemporalUnit#getDuration() duration}
+      * that divides into the length of a standard day without remainder.
+      * This includes all supplied time units on {@link ChronoUnit} and
+      * {@link ChronoUnit#DAYS DAYS}. Other ChronoUnits throw an exception.
+      * <p>
+      * This instance is immutable and unaffected by this method call.
+      *
+      * @param unit the unit to truncate to, not null
+      * @return a {@code Duration} based on this duration with the time truncated, not null
+      * @throws DateTimeException if the unit is invalid for truncation
+      * @throws UnsupportedTemporalTypeException if the unit is not supported
+      */
+     public Duration truncatedTo(TemporalUnit unit) {
+         Objects.requireNonNull(unit, "unit");
+         if (unit == ChronoUnit.SECONDS) {
+             return new Duration(seconds, 0);
+         } else if (unit == ChronoUnit.NANOS) {
+             return this;
+         }
+         Duration unitDur = unit.getDuration();
+         if (unitDur.getSeconds() > LocalTime.SECONDS_PER_DAY) {
+             throw new UnsupportedTemporalTypeException("Unit is too large to be used for truncation");
+         }
+         long dur = unitDur.toNanos();
+         if ((LocalTime.NANOS_PER_DAY % dur) != 0) {
+             throw new UnsupportedTemporalTypeException("Unit must divide into a standard day without remainder");
+         }
+         long nod = (seconds % LocalTime.SECONDS_PER_DAY) * LocalTime.NANOS_PER_SECOND + nanos;
+         long result = Math.floorDiv(nod, dur) * dur ;
+         return plusNanos(result - nod);
+     }
+ 
      //-----------------------------------------------------------------------
      /**
       * Compares this duration to the specified {@code Duration}.
       * <p>
       * The comparison is based on the total length of the durations.