Summary

Add explicit specification to Types.directSupertypes on how java.lang.Object is handled.

Problem

java.lang.Object is a special case in for the direct super type relationship. The specification for Types.directSupertypes does not explicitly mention this case; although the correct behavior can be inferred from the existing specification.

Solution

Add explicit text stating java.lang.Object has no direct super types.

Specification

diff --git a/src/java.compiler/share/classes/javax/lang/model/util/Types.java b/src/java.compiler/share/classes/javax/lang/model/util/Types.java
index 02c7085bd8c..cd5a9a848a9 100644
--- a/src/java.compiler/share/classes/javax/lang/model/util/Types.java
+++ b/src/java.compiler/share/classes/javax/lang/model/util/Types.java
@@ -133,6 +133,10 @@ public interface Types {
      * will appear last in the list. For an interface type with no direct
      * super-interfaces, a type mirror representing {@code java.lang.Object}
      * is returned.
+     * The type {@code java.lang.Object} has no direct supertype
+     * ({@jls 8.1.4}, {@jls 8.1.5}) so an empty list is returned for the direct
+     * supertypes of a type mirror representing {@code
+     * java.lang.Object}.
      *
      * @param t  the type being examined
      * @return the direct supertypes, or an empty list if none