RFR: 8172720: Collections.SingletonList::hashCode not spec-compliant

[Claes Redestad]

Hi,

there was an issue with my patch for JDK-8037325 where the
hashCode implemented for Collections.SingletonList was not
compliant with specification, which breaks certain tests.
Bug: https://bugs.openjdk.java.net/browse/JDK-8172720

Trivial fix:

diff -r 59e5101730c8 src/java.base/share/classes/java/util/Collections.java
--- a/src/java.base/share/classes/java/util/Collections.java	Thu Jan 12 
13:38:27 2017 +0100
+++ b/src/java.base/share/classes/java/util/Collections.java	Thu Jan 12 
16:39:44 2017 +0100
@@ -4859,7 +4859,7 @@
         }
         @Override
         public int hashCode() {
-            return Objects.hashCode(element);
+            return 31 + Objects.hashCode(element);
         }
     }