equals-hashcode: equals/hashCode contract demos, missing hashCode and constant-hash costs, mutable keys, records, JPA entity id trap, 13 contract tests

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b66uwsWr9B1ouyrzUh

equals-hashcode/output/05-records.txt

@@ -0,0 +1,23 @@
+== generated equals/hashCode ==
+a.equals(b)                = true
+a.hashCode() == b.hashCode() = true
+new HashSet of both, size  = 1
+a == b                     = false
+
+== array component: reference equality ==
+w1.equals(w2) = false
+same array shared: true
+
+== mutable List component: equals works, hashCode can change ==
+hashCode before = 4714, after list.add(3) = 34537
+record in HashSet, list mutated -> contains = false
+
+== doubles compare with Double.compare semantics ==
+NaN record equals NaN record = true
+Double.NaN == Double.NaN     = false
+0.0 record equals -0.0 record = false
+0.0 == -0.0                   = true
+
+== overriding equals in a record ==
+t1.equals(t2) = true
+toString still shows both fields: Tagged[isbn=1, title=Effective Java 3e]