src/java.base/share/classes/java/util/Collections.java

*** 457,467 ****
          int size = list.size();
          if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
              for (int i=size; i>1; i--)
                  swap(list, i-1, rnd.nextInt(i));
          } else {
!             Object arr[] = list.toArray();
  
              // Shuffle array
              for (int i=size; i>1; i--)
                  swap(arr, i-1, rnd.nextInt(i));
  
--- 457,467 ----
          int size = list.size();
          if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
              for (int i=size; i>1; i--)
                  swap(list, i-1, rnd.nextInt(i));
          } else {
!             Object[] arr = list.toArray();
  
              // Shuffle array
              for (int i=size; i>1; i--)
                  swap(arr, i-1, rnd.nextInt(i));
  
*** 5099,5108 ****
--- 5099,5127 ----
                  throw new IllegalArgumentException("fromIndex(" + fromIndex +
                                                     ") > toIndex(" + toIndex + ")");
              return new CopiesList<>(toIndex - fromIndex, element);
          }
  
+         @Override
+         public int hashCode() {
+             if (n == 0) return 1;
+             // hashCode of n repeating elements is 31^n + elementHash * Sum(31^k, k = 0..n-1)
+             // this implementation completes in O(log(n)) steps taking advantage of
+             // 31^(2*n) = (31^n)^2 and Sum(31^k, k = 0..(2*n-1)) = Sum(31^k, k = 0..n-1) * (31^n + 1) 
+             int pow = 31;
+             int sum = 1;
+             for (int i = Integer.numberOfLeadingZeros(n) + 1; i < Integer.SIZE; i++) {
+                 sum *= pow + 1;
+                 pow *= pow;
+                 if ((n << i) < 0) {
+                     pow *= 31;
+                     sum = sum * 31 + 1;
+                 }
+             }
+             return pow + sum * (element == null ? 0 : element.hashCode());
+         }
+ 
          // Override default methods in Collection
          @Override
          public Stream<E> stream() {
              return IntStream.range(0, n).mapToObj(i -> element);
          }