Add sealed module: modelling domains with sealed types and exhaustive switch

Payment model, permits and the three modifiers, default-branch trap, generic and recursive hierarchies, visitor comparison, run-time enforcement, modules. Transcripts from JDK 21, 25 and 27. Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01TF9JWFvJSNm6HVzswzZU5a
2026-09-24 12:03:59 +00:00
parent 65a4bbbbe3
commit ff6130bede
38 changed files with 638 additions and 0 deletions
@@ -0,0 +1,130 @@
+$ javac broken/WalletNotHandled.java     (21.0.10+7-Ubuntu-124.04)
+broken/WalletNotHandled.java:10: error: the switch expression does not cover all possible input values
+        return switch (p) {
+               ^
+1 error
+
+$ javac broken/WalletNotHandled.java     (25.0.4.1+1-LTS)
+broken/WalletNotHandled.java:10: error: the switch expression does not cover all possible input values
+        return switch (p) {
+               ^
+1 error
+
+$ javac broken/WalletNotHandled.java     (27+35)
+broken/WalletNotHandled.java:10: error: the switch expression does not cover all possible input values
+        return switch (p) {
+               ^
+  missing patterns:
+      Wallet _
+1 error
+
+$ javac broken/NotPermitted.java     (21.0.10+7-Ubuntu-124.04)
+broken/NotPermitted.java:5: error: class is not allowed to extend sealed class: Payment (as it is not listed in its 'permits' clause)
+    record Cheque(long amount) implements Payment {}      // not in the permits clause
+    ^
+1 error
+
+$ javac broken/NotPermitted.java     (25.0.4.1+1-LTS)
+broken/NotPermitted.java:5: error: class is not allowed to extend sealed class: Payment (as it is not listed in its 'permits' clause)
+    record Cheque(long amount) implements Payment {}      // not in the permits clause
+    ^
+1 error
+
+$ javac broken/NotPermitted.java     (27+35)
+broken/NotPermitted.java:5: error: class is not allowed to extend sealed class: Payment (as it is not listed in its 'permits' clause)
+    record Cheque(long amount) implements Payment {}      // not in the permits clause
+    ^
+1 error
+
+$ javac broken/MissingModifier.java     (21.0.10+7-Ubuntu-124.04)
+broken/MissingModifier.java:3: error: sealed, non-sealed or final modifiers expected
+    class Card implements Payment {}                      // must say final, sealed or non-sealed
+    ^
+1 error
+
+$ javac broken/MissingModifier.java     (25.0.4.1+1-LTS)
+broken/MissingModifier.java:3: error: sealed, non-sealed or final modifiers expected
+    class Card implements Payment {}                      // must say final, sealed or non-sealed
+    ^
+1 error
+
+$ javac broken/MissingModifier.java     (27+35)
+broken/MissingModifier.java:3: error: sealed, non-sealed or final modifiers expected
+    class Card implements Payment {}                      // must say final, sealed or non-sealed
+    ^
+1 error
+
+$ javac broken/NoSubclass.java     (21.0.10+7-Ubuntu-124.04)
+broken/NoSubclass.java:2: error: sealed class must have subclasses
+    sealed interface Payment {}                           // no permits clause and no subtype in this file
+           ^
+1 error
+
+$ javac broken/NoSubclass.java     (25.0.4.1+1-LTS)
+broken/NoSubclass.java:2: error: sealed class must have subclasses
+    sealed interface Payment {}                           // no permits clause and no subtype in this file
+           ^
+1 error
+
+$ javac broken/NoSubclass.java     (27+35)
+broken/NoSubclass.java:2: error: sealed class must have subclasses
+    sealed interface Payment {}                           // no permits clause and no subtype in this file
+           ^
+1 error
+
+$ javac broken/NonSealedWrongPlace.java     (21.0.10+7-Ubuntu-124.04)
+broken/NonSealedWrongPlace.java:3: error: non-sealed modifier not allowed here
+    non-sealed class Oops implements Plain {}             // non-sealed only makes sense under a sealed supertype
+               ^
+  (class NonSealedWrongPlace.Oops does not have any sealed supertypes)
+1 error
+
+$ javac broken/NonSealedWrongPlace.java     (25.0.4.1+1-LTS)
+broken/NonSealedWrongPlace.java:3: error: non-sealed modifier not allowed here
+    non-sealed class Oops implements Plain {}             // non-sealed only makes sense under a sealed supertype
+               ^
+  (class NonSealedWrongPlace.Oops does not have any sealed supertypes)
+1 error
+
+$ javac broken/NonSealedWrongPlace.java     (27+35)
+broken/NonSealedWrongPlace.java:3: error: non-sealed modifier not allowed here
+    non-sealed class Oops implements Plain {}             // non-sealed only makes sense under a sealed supertype
+               ^
+  (class NonSealedWrongPlace.Oops does not have any sealed supertypes)
+1 error
+
+$ javac broken/AnonymousSealed.java     (21.0.10+7-Ubuntu-124.04)
+broken/AnonymousSealed.java:5: error: anonymous classes must not extend sealed classes
+        return new Payment() {};                          // an anonymous class is a subtype nobody listed
+                             ^
+1 error
+
+$ javac broken/AnonymousSealed.java     (25.0.4.1+1-LTS)
+broken/AnonymousSealed.java:5: error: anonymous classes must not extend sealed classes
+        return new Payment() {};                          // an anonymous class is a subtype nobody listed
+                             ^
+1 error
+
+$ javac broken/AnonymousSealed.java     (27+35)
+broken/AnonymousSealed.java:5: error: anonymous classes must not extend sealed classes
+        return new Payment() {};                          // an anonymous class is a subtype nobody listed
+                             ^
+1 error
+
+$ javac broken/xpkg/a/Base.java broken/xpkg/b/Impl.java     (21.0.10+7-Ubuntu-124.04)
+broken/xpkg/a/Base.java:2: error: class Base in unnamed module cannot extend a sealed class in a different package
+public sealed interface Base permits b.Impl {}
+                                      ^
+1 error
+
+$ javac broken/xpkg/a/Base.java broken/xpkg/b/Impl.java     (25.0.4.1+1-LTS)
+broken/xpkg/a/Base.java:2: error: class Base in unnamed module cannot extend a sealed class in a different package
+public sealed interface Base permits b.Impl {}
+                                      ^
+1 error
+
+$ javac broken/xpkg/a/Base.java broken/xpkg/b/Impl.java     (27+35)
+broken/xpkg/a/Base.java:2: error: class Base in unnamed module cannot extend a sealed class in a different package
+public sealed interface Base permits b.Impl {}
+                                      ^
+1 error