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

@@ -153,11 +153,11 @@
      * It is equivalent to {@code system(ZoneOffset.UTC)}.
      *
      * @return a clock that uses the best available system clock in the UTC zone, not null
      */
     public static Clock systemUTC() {
-        return new SystemClock(ZoneOffset.UTC);
+        return SystemClock.UTC;
     }
 
     /**
      * Obtains a clock that returns the current instant using the best available
      * system clock, converting to date and time using the default time-zone.

@@ -196,10 +196,13 @@
      * @param zone  the time-zone to use to convert the instant to date-time, not null
      * @return a clock that uses the best available system clock in the specified zone, not null
      */
     public static Clock system(ZoneId zone) {
         Objects.requireNonNull(zone, "zone");
+        if (zone == ZoneOffset.UTC) {
+            return SystemClock.UTC;
+        }
         return new SystemClock(zone);
     }
 
     //-------------------------------------------------------------------------
     /**

@@ -449,10 +452,12 @@
      */
     static final class SystemClock extends Clock implements Serializable {
         private static final long serialVersionUID = 6740630888130243051L;
         private static final long OFFSET_SEED =
                 System.currentTimeMillis()/1000 - 1024; // initial offest
+        static final SystemClock UTC = new SystemClock(ZoneOffset.UTC);
+
         private final ZoneId zone;
         // We don't actually need a volatile here.
         // We don't care if offset is set or read concurrently by multiple
         // threads - we just need a value which is 'recent enough' - in other
         // words something that has been updated at least once in the last