refactor: port default content to java

Preserve the exact built-in factory, material, and remap registrations.

JAVA_MIGRATION.md

@@ -812,3 +812,11 @@ generated-trait compatibility work. Scala-runtime removal remains a later projec
   unchanged; only the actual client rendering remains manual.
 - All 177 plain-JVM and all 92 Java 8 Forge dedicated-server tests pass. This inert singleton is not a meaningful
   focused performance target; `DefaultContent.scala` is the next medium-risk target.
+- Characterized `DefaultContent` against untouched Scala. One plain-JVM case freezes its one-method static and
+  companion surfaces. Two Forge cases freeze the five microblock factories and IDs, all 103 sorted built-in
+  materials, their exact implementation types and the complete legacy-name remap table.
+- Ported the singleton to a Java facade/companion pair while continuing to use the existing `BlockMicroMaterial$`
+  overloads and Scala ranges. Registration contents, ordering and the historical meta-0-only `log2`/`leaves2`
+  overload behavior are unchanged.
+- All 178 plain-JVM and all 94 Java 8 Forge dedicated-server tests pass. Pre-init-only registration is not a meaningful
+  focused performance target; `GrassMicroMaterial.scala` is the next material unit.

JAVA_MIGRATION_DIVERGENCES.md

@@ -2080,3 +2080,39 @@ use `MissingMicroMaterial$.MODULE$`; static calls retain their original names an
 - Java 8 Forge dedicated-server suite: 92 tests, 0 failures, 0 errors.
 - Raw `javap` comparison confirms identical callable public names/descriptors and the emitted class list is unchanged.
 - Missing-texture icon loading and face rendering require a client and remain on the manual checklist.
+
+## 2026-08-31 — DefaultContent Java port
+
+The built-in microblock registration singleton is now a Java static facade plus Java companion. `MicroblockMod$`
+continues to call `DefaultContent$.MODULE$.load()` during pre-init.
+
+### Observable behavior
+
+No known runtime divergence. The same face, hollow, corner and edge classes retain IDs 0 through 3, and the post
+class remains registered without a common-class ID. Their five multipart type names and exact singleton factories are
+unchanged.
+
+The material registry still receives the same 103 entries, sorts them by name during post-init, and maps every legacy
+unlocalized key to the same registry key. Grass still uses `GrassMicroMaterial`, mycelium still uses
+`TopMicroMaterial`, and the missing key still maps to `MissingMicroMaterial$.MODULE$`. The Java implementation calls
+the existing `BlockMicroMaterial$` overloads with Scala inclusive ranges, preserving the reference's meta coverage.
+In particular, the three-argument overload used for `log2` and `leaves2` still registers only metadata zero despite
+receiving ranges through one; this port deliberately does not combine a behavior fix with the language conversion.
+
+### ABI and source compatibility
+
+`DefaultContent` retains its sole public static `load()V`; `DefaultContent$` retains `MODULE$` and the matching public
+instance method. Both jars emit exactly `DefaultContent.class` and `DefaultContent$.class`. No audited shipping
+consumer references either type.
+
+Accepted classfile-only differences are removed Scala signature/marker attributes, a private constructor on the
+facade, and a class initializer without Scala's `ACC_PUBLIC` flag. A class initializer is JVM-only and is not a
+callable member.
+
+### Validation
+
+- `DefaultContentCharacterizationTest`: 1 plain-JVM test, unchanged from the Scala baseline.
+- `DefaultContentFunctionalTest`: 2 Forge tests, unchanged from the Scala baseline.
+- Complete plain-JVM suite: 178 tests, 0 failures, 0 errors.
+- Java 8 Forge dedicated-server suite: 94 tests, 0 failures, 0 errors.
+- Raw `javap` comparison confirms identical callable public names/descriptors and the emitted class list is unchanged.

JAVA_MIGRATION_HANDOFF.md

@@ -12,8 +12,8 @@ what breaks, and what is left. The other documents hold the reasoning.
 | `JAVA_MIGRATION_MANUAL_CHECKS.md` | What no automated test can cover, and must be checked by hand in a client |
 | `JAVA_MIGRATION_PROFILE.md` | The focused baseline, first measured result, findings, and exact rerun command |
 
-Branch: `algent/java`. Base: `master`. 102 commits including the incremental-version build fix and separate
-characterization and port commits for `MissingMicroMaterial`.
+Branch: `algent/java`. Base: `master`. 104 commits including the incremental-version build fix and separate
+characterization and port commits for `DefaultContent`.
 
 ## The one rule that matters
 
@@ -67,7 +67,7 @@ awk -F'"' '/<testsuite /{t+=$4;f+=$8;e+=$10} END{print "tests="t" failures="f" e
 grep -o 'tests="[0-9]*" skipped="[0-9]*" failures="[0-9]*" errors="[0-9]*"' run/server/junit-out/TEST-*.xml
 ```
 
-Current baseline: **177 plain-JVM tests and 92 Java 8 Forge dedicated-server tests passing.** The ignored local server
+Current baseline: **178 plain-JVM tests and 94 Java 8 Forge dedicated-server tests passing.** The ignored local server
 EULA is accepted in this checkout.
 
 ### ABI diff against the reference
@@ -243,7 +243,8 @@ All eight load-bearing `$class` helpers from the inventory, both registries, and
 `TRedstoneTile`, `TTileChangeTile`, `TFluidHandlerTile`, `TIInventoryTile`/`JInventoryTile`, `TileMultipartClient`, and
 `TRandomDisplayTickTile` Java-trait ports, plus `MultipartCompatiblity`/`MCPCCompatModule`, `MultipartMod`,
 `MultipartEventHandler`, `MicroblockMod`, `MicroblockEventHandler`, and the complete `MicroblockPH`/
-`MicroblockCPH`/`MicroblockSPH` packet-handler unit, plus `MultipartSaveLoad` and `MissingMicroMaterial`.
+`MicroblockCPH`/`MicroblockSPH` packet-handler unit, plus `MultipartSaveLoad`, `MissingMicroMaterial`, and
+`DefaultContent`.
 
 Plus the six marker interfaces: `TSlottedPart`, `IRandomDisplayTick`, `INeighborTileChange`, `TRandomUpdateTick`,
 `ISidedHollowConnect`, `IMicroMaterialRender`, plus `MultipartHelper`, `TileCache`, `PacketScheduler` and the `ControlKeyModifer` pair.
@@ -258,7 +259,7 @@ across the port. It is also where the two shim constraints in the gotchas list w
 `rayTraceAll`'s index production is now characterized, closing the gap the read-path cleanup left: the index written
 into `ExtendedMOP.data` is what `reduceMOP` hands back to every click, activate, harvest and pick block.
 
-112 Java files, 30 Scala files, ~4,871 Scala lines left (non-blank; that is the metric this figure has always used).
+114 Java files, 29 Scala files, ~4,816 Scala lines left (non-blank; that is the metric this figure has always used).
 
 ## What is left, and in what order
 
@@ -382,18 +383,23 @@ descriptors, `MODULE$`, `IMicroMaterial`, and the three client-only boundaries.
 shape and inert values; one Forge test proves that `DefaultContent` registers the same singleton after client methods
 and state are stripped on a dedicated server. The missing-texture render path remains client-manual.
 
+`DefaultContent` is now Java. Its sole static/companion method and both emitted singleton types retain their exact
+shape. One plain-JVM test freezes that ABI; two Forge tests freeze all five microblock factories, common IDs, the 103
+sorted built-in materials and every legacy remap. The historical `log2`/`leaves2` meta-0-only overload behavior is
+explicitly preserved rather than repaired during the port.
+
 **Medium.** The `handler` packages on both sides, `ItemMicroPart`,
 `MicroblockPlacement`, `PlacementGrids`, `BlockMicroMaterial`, `ConfigContent`,
-`DefaultContent`.
+and the remaining material/render units.
 
 **Phase 5 is complete.** There are no Scala files left in `multipart/scalatraits/`. The client pair required the first
 narrow generator relaxation: Java-trait parent linearization, explicit field-accessor recognition, and exclusion of
 transient runtime caches from generated copying.
 
-Take `microblock/DefaultContent.scala` next. At 55 nonblank lines it is the smallest remaining unit named in the
-medium-risk queue. Freeze the exact facade/companion surface and the complete ordered built-in class/material
-registration result before changing it; retain the existing remaps and exact `MissingMicroMaterial$.MODULE$`
-registration. Keep the characterization and port commits separate.
+Take `microblock/GrassMicroMaterial.scala` next. At 56 nonblank lines it is the smallest remaining material unit and
+contains both `GrassMicroMaterial` and `TopMicroMaterial`. Freeze constructors, public fields/accessors, inherited
+`BlockMicroMaterial` behavior, client-only boundaries and side-dependent UV/render routing. Keep actual face colour,
+overlay and texture rendering on the client manual checklist, and keep the characterization and port commits separate.
 
 **Phase 6/7, last.** `Microblock` and the microblock shape hierarchy, `MicroblockGenerator`, `MultipartGenerator`, and
 all of `multipart/asm/`. The ASM subsystem should be last; freeze generated-class fixtures before touching it.

src/main/scala/codechicken/microblock/DefaultContent$.java

@@ -0,0 +1,67 @@
+package codechicken.microblock;
+
+import net.minecraft.init.Blocks;
+
+import scala.collection.immutable.Range$;
+
+public final class DefaultContent$ {
+
+    public static final DefaultContent$ MODULE$ = new DefaultContent$();
+
+    private DefaultContent$() {}
+
+    public void load() {
+        FaceMicroClass$.MODULE$.register(0);
+        HollowMicroClass$.MODULE$.register(1);
+        CornerMicroClass$.MODULE$.register(2);
+        EdgeMicroClass$.MODULE$.register(3);
+        PostMicroClass$.MODULE$.register();
+
+        BlockMicroMaterial$ materials = BlockMicroMaterial$.MODULE$;
+        materials.createAndRegister(Blocks.stone, 0);
+        materials.createAndRegister(Blocks.dirt, Range$.MODULE$.inclusive(0, 2));
+        materials.createAndRegister(Blocks.cobblestone, 0);
+        materials.createAndRegister(Blocks.planks, Range$.MODULE$.inclusive(0, 5));
+        materials.createAndRegister(Blocks.log, Range$.MODULE$.inclusive(0, 3));
+        materials.createAndRegister(Blocks.log2, Range$.MODULE$.inclusive(0, 1), "tile.log2");
+        materials.createAndRegister(Blocks.leaves, Range$.MODULE$.inclusive(0, 3));
+        materials.createAndRegister(Blocks.leaves2, Range$.MODULE$.inclusive(0, 1), "tile.leaves2");
+        materials.createAndRegister(Blocks.sponge, 0);
+        materials.createAndRegister(Blocks.glass, 0);
+        materials.createAndRegister(Blocks.lapis_block, 0);
+        materials.createAndRegister(Blocks.sandstone, Range$.MODULE$.inclusive(0, 2));
+        materials.createAndRegister(Blocks.wool, Range$.MODULE$.inclusive(0, 15));
+        materials.createAndRegister(Blocks.gold_block, 0);
+        materials.createAndRegister(Blocks.iron_block, 0);
+        materials.createAndRegister(Blocks.brick_block, 0);
+        materials.createAndRegister(Blocks.bookshelf, 0);
+        materials.createAndRegister(Blocks.mossy_cobblestone, 0);
+        materials.createAndRegister(Blocks.obsidian, 0);
+        materials.createAndRegister(Blocks.diamond_block, 0);
+        materials.createAndRegister(Blocks.ice, 0);
+        materials.createAndRegister(Blocks.snow, 0);
+        materials.createAndRegister(Blocks.clay, 0);
+        materials.createAndRegister(Blocks.netherrack, 0);
+        materials.createAndRegister(Blocks.soul_sand, 0);
+        materials.createAndRegister(Blocks.glowstone, 0);
+        materials.createAndRegister(Blocks.stonebrick, Range$.MODULE$.inclusive(0, 3));
+        materials.createAndRegister(Blocks.nether_brick, 0);
+        materials.createAndRegister(Blocks.end_stone, 0);
+        materials.createAndRegister(Blocks.emerald_block, 0);
+        materials.createAndRegister(Blocks.redstone_block, 0);
+        materials.createAndRegister(Blocks.quartz_block, 0);
+        materials.createAndRegister(Blocks.stained_hardened_clay, Range$.MODULE$.inclusive(0, 15));
+        materials.createAndRegister(Blocks.hardened_clay, 0);
+        materials.createAndRegister(Blocks.coal_block, 0);
+        materials.createAndRegister(Blocks.packed_ice, 0);
+        materials.createAndRegister(Blocks.stained_glass, Range$.MODULE$.inclusive(0, 15));
+
+        MicroMaterialRegistry.remapName(materials.oldKey(Blocks.grass), materials.materialKey(Blocks.grass));
+        MicroMaterialRegistry.registerMaterial(new GrassMicroMaterial(), materials.materialKey(Blocks.grass));
+        MicroMaterialRegistry.remapName(materials.oldKey(Blocks.mycelium), materials.materialKey(Blocks.mycelium));
+        MicroMaterialRegistry
+                .registerMaterial(new TopMicroMaterial(Blocks.mycelium, 0), materials.materialKey(Blocks.mycelium));
+
+        MicroMaterialRegistry.registerMaterial(MissingMicroMaterial$.MODULE$, MissingMicroMaterial.key());
+    }
+}

src/main/scala/codechicken/microblock/DefaultContent.java

@@ -0,0 +1,10 @@
+package codechicken.microblock;
+
+public final class DefaultContent {
+
+    private DefaultContent() {}
+
+    public static void load() {
+        DefaultContent$.MODULE$.load();
+    }
+}

src/main/scala/codechicken/microblock/DefaultContent.scala

@@ -1,60 +0,0 @@
-package codechicken.microblock
-
-import net.minecraft.init.Blocks._
-import BlockMicroMaterial._
-import MicroMaterialRegistry._
-
-object DefaultContent {
-  def load() {
-    FaceMicroClass.register(0)
-    HollowMicroClass.register(1)
-    CornerMicroClass.register(2)
-    EdgeMicroClass.register(3)
-    PostMicroClass.register()
-
-    createAndRegister(stone)
-    createAndRegister(dirt, 0 to 2)
-    createAndRegister(cobblestone)
-    createAndRegister(planks, 0 to 5)
-    createAndRegister(log, 0 to 3)
-    createAndRegister(log2, 0 to 1, "tile.log2")
-    createAndRegister(leaves, 0 to 3)
-    createAndRegister(leaves2, 0 to 1, "tile.leaves2")
-    createAndRegister(sponge)
-    createAndRegister(glass)
-    createAndRegister(lapis_block)
-    createAndRegister(sandstone, 0 to 2)
-    createAndRegister(wool, 0 to 15)
-    createAndRegister(gold_block)
-    createAndRegister(iron_block)
-    createAndRegister(brick_block)
-    createAndRegister(bookshelf)
-    createAndRegister(mossy_cobblestone)
-    createAndRegister(obsidian)
-    createAndRegister(diamond_block)
-    createAndRegister(ice)
-    createAndRegister(snow)
-    createAndRegister(clay)
-    createAndRegister(netherrack)
-    createAndRegister(soul_sand)
-    createAndRegister(glowstone)
-    createAndRegister(stonebrick, 0 to 3)
-    createAndRegister(nether_brick)
-    createAndRegister(end_stone)
-    createAndRegister(emerald_block)
-    createAndRegister(redstone_block)
-    createAndRegister(quartz_block)
-    createAndRegister(stained_hardened_clay, 0 to 15)
-    createAndRegister(hardened_clay)
-    createAndRegister(coal_block)
-    createAndRegister(packed_ice)
-    createAndRegister(stained_glass, 0 to 15)
-
-    MicroMaterialRegistry.remapName(oldKey(grass), materialKey(grass))
-    registerMaterial(new GrassMicroMaterial, materialKey(grass))
-    MicroMaterialRegistry.remapName(oldKey(mycelium), materialKey(mycelium))
-    registerMaterial(new TopMicroMaterial(mycelium), materialKey(mycelium))
-
-    registerMaterial(MissingMicroMaterial$.MODULE$, MissingMicroMaterial.key())
-  }
-}