test/jdk/java/util/Collections/NCopies.java

*** 1,7 ****
  /*
!  * Copyright (c) 2005, 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
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
--- 1,7 ----
  /*
!  * 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
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
*** 27,37 ****
--- 27,39 ----
   * @summary Test Collections.nCopies
   * @author  Martin Buchholz
   */
  
  import java.util.Collections;
+ import java.util.AbstractList;
  import java.util.List;
+ import java.util.Objects;
  
  public class NCopies {
      static volatile int passed = 0, failed = 0;
  
      static void fail(String msg) {
*** 80,99 ****
--- 82,128 ----
              check(sa[sa.length-1].equals("foo"));
              check(x.get(x.size()/2).equals("foo"));
              checkEmpty(x.subList(x.size()/2, x.size()/2));
      }
      
+     private static <T> List<T> 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) {
+                 Objects.checkIndex(index, n);
+                 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()");
+             }
+         }
+     }
+ 
      public static void main(String[] args) {
          try {
              List<String> empty = Collections.nCopies(0, "foo");
              checkEmpty(empty);
              checkEmpty(empty.subList(0,0));
  
              List<String> foos = Collections.nCopies(42, "foo");
              check(foos.size() == 42);
              checkFoos(foos.subList(foos.size()/2, foos.size()-1));
  
+             checkHashCode();
+ 
          } catch (Throwable t) { unexpected(t); }
  
          System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
          if (failed > 0) throw new Error("Some tests failed");
      }