IdentityHashCode in HashMap's bucket

Question

In the implementation details of HashMap, I can read:

When using comparators on insertion, to keep a
 * total ordering (or as close as is requir         


        

Answer 1

The bucket will use identityHashCode during insertion, but lookup uses only hash codes and compare() calls (if available). This means it sometimes needs to scan both subtrees of a node.

The lookup logic looks line this

do {
  if (... keys are equal or can be compared ...) {
    // Go left, right or return the current node
    ...
  } else if ((q = pr.find(h, k, kc)) != null)
    // Search the right subtree recursively
    return q;
  else
   // Go to the left subtree
   p = pl;
} while (p != null);

See http://hg.openjdk.java.net/jdk10/jdk10/jdk/file/ffa11326afd5/src/java.base/share/classes/java/util/HashMap.java#l1901 and note that tieBreakOrder() (the method responsible for comparing identityHashCodes is not invoked anywhere in find().