diff --git a/src/share/classes/java/util/Collections.java b/src/share/classes/java/util/Collections.java index 79159eaa1106df60729e76d2c8ed099146360db5..3ab4c5ec0681ccce557bafbabea38e10dc4c1cf0 100644 --- a/src/share/classes/java/util/Collections.java +++ b/src/share/classes/java/util/Collections.java @@ -459,7 +459,7 @@ public class Collections { for (int i=size; i>1; i--) swap(list, i-1, rnd.nextInt(i)); } else { - Object arr[] = list.toArray(); + Object[] arr = list.toArray(); // Shuffle array for (int i=size; i>1; i--) @@ -5062,6 +5062,53 @@ public class Collections { 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 + public boolean equals(Object o) { + if (o == this) + return true; + if (o instanceof CopiesList) { + CopiesList other = (CopiesList) o; + return n == other.n && (n == 0 || eq(element, other.element)); + } + if (!(o instanceof List)) + return false; + + int remaining = n; + E e = element; + Iterator itr = ((List) o).iterator(); + if (e == null) { + while (itr.hasNext() && remaining-- > 0) { + if (itr.next() != null) + return false; + } + } else { + while (itr.hasNext() && remaining-- > 0) { + if (!e.equals(itr.next())) + return false; + } + } + return remaining == 0 && !itr.hasNext(); + } + // Override default methods in Collection @Override public Stream stream() { diff --git a/test/java/util/Collections/NCopies.java b/test/java/util/Collections/NCopies.java index db1a61b0dc9eecb44b39e6b73bd419dfc51ca379..2458386fb663a9884cdb6a1f23afbab3e767aade 100644 --- a/test/java/util/Collections/NCopies.java +++ b/test/java/util/Collections/NCopies.java @@ -1,5 +1,5 @@ /* - * Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved. + * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it @@ -82,6 +82,56 @@ public class NCopies { checkEmpty(x.subList(x.size()/2, x.size()/2)); } + private static List referenceNCopies(int n, T o) { + // A simplest correct implementation of nCopies to compare with the actual optimized implementation + return new AbstractList() { + public int size() { return n; } + + public T get(int index) { + check(0 <= index && index < n, "Index is incorrect"); + return o; + } + }; + } + + private static void checkHashCode() { + int[] sizes = {0, 1, 2, 3, 5, 10, 31, 32, 100, 1000}; + String[] elements = {null, "non-null"}; + for (int size : sizes) { + for (String element : elements) { + int expectedHashCode = referenceNCopies(size, element).hashCode(); + int actualHashCode = Collections.nCopies(size, element).hashCode(); + check(expectedHashCode == actualHashCode, + "Collections.nCopies(" + size + ", " + element + ").hashCode()"); + } + } + } + + private static void checkEquals() { + int[][] sizePairs = {{0, 0}, {0, 1}, {1, 0}, {1, 1}, {1, 2}, {2, 1}}; + String[] elements = {null, "non-null"}; + for (int[] pair : sizePairs) { + for (String element : elements) { + boolean equal = pair[0] == pair[1]; + String msg = "[" + pair[0] + ", " + element + "] <=> [" + pair[1] + ", " + element + "]"; + check(equal == Collections.nCopies(pair[0], element).equals(Collections.nCopies(pair[1], element)), msg); + check(equal == Collections.nCopies(pair[0], element).equals(referenceNCopies(pair[1], element)), msg); + check(equal == referenceNCopies(pair[0], element).equals(Collections.nCopies(pair[1], element)), msg); + } + } + List nulls = Collections.nCopies(10, null); + List nonNulls = Collections.nCopies(10, "non-null"); + List nullsButOne = new ArrayList<>(nulls); + nullsButOne.set(9, "non-null"); + List nonNullsButOne = new ArrayList<>(nonNulls); + nonNullsButOne.set(9, null); + check(!nulls.equals(nonNulls)); + check(!nulls.equals(nullsButOne)); + check(!nulls.equals(nonNullsButOne)); + check(!nonNulls.equals(nonNullsButOne)); + check(Collections.nCopies(0, null).equals(Collections.nCopies(0, "non-null"))); + } + public static void main(String[] args) { try { List empty = Collections.nCopies(0, "foo"); @@ -92,6 +142,10 @@ public class NCopies { check(foos.size() == 42); checkFoos(foos.subList(foos.size()/2, foos.size()-1)); + checkHashCode(); + + checkEquals(); + } catch (Throwable t) { unexpected(t); } System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);