Deduplicate Java/Scala template projects in skills [skip ci] (#15111)

Fixes #15094.

### Description

This removes the Java template project provided with the skills, making
the Scala project the ground truth for any input JVM UDF. The
instructions are adjusted accordingly. Jacoco and Hive support is moved
over to the Scala templates.

### Checklists

Documentation
- [X] Updated for new or modified user-facing features or behaviors
- [ ] No user-facing change

Testing
- [ ] Added or modified tests to cover new code paths
- [ ] Covered by existing tests
(Please provide the names of the existing tests in the PR description.)
- [X] Not required

Performance
- [ ] Tests ran and results are added in the PR description
- [ ] Issue filed with a link in the PR description
- [X] Not required

---------

Signed-off-by: Rishi Chandra <rishic@nvidia.com>

Author: rishic3

skills/README.md

@@ -110,7 +110,7 @@ Once you've installed the skills, try the workflow with one of the provided exam
       Results
 
       - Project directory: FormatPhoneUDF/
-      - Unit test: FormatPhoneUDF/src/test/java/com/udf/UnitTest.java
+      - Unit test: FormatPhoneUDF/src/test/scala/com/udf/UnitTest.scala
       - Status: All tests passing
       - Test coverage: 12 cases
    ```

skills/docs/dev/VERSIONS.md

@@ -2,20 +2,7 @@
 
 ## Files To Update
 
-### Java udf-gen-test Maven template
-
-File: `skills/udf-gen-test/templates/java/pom.xml`
-
-Update these properties together:
-
-- `<scala.binary.version>`
-- `<spark.version>`
-- `<rapids4spark.version>`
-- `<cuda.version>` if the RAPIDS artifact classifier changes
-- `<cudf.git.branch>`
-- `<rapids.cmake.branch>`
-
-### Scala udf-gen-test Maven template
+### udf-gen-test Maven template
 
 File: `skills/udf-gen-test/templates/scala/pom.xml`
 

skills/udf-benchmark/SKILL.md

@@ -28,7 +28,7 @@ Derive `<CamelName>` and `<snake_name>` from the UDF class name.
 
 ## Step 1: Implement BenchUtils
 
-Read `src/main/<java|scala>/com/udf/bench/BenchUtils.<java|scala>`. Replace placeholders with the actual camel/snake UDF name.
+Read `src/main/scala/com/udf/bench/BenchUtils.scala`. Replace placeholders with the actual camel/snake UDF name.
 
 Fill in the TODO methods following the docstrings. For variable-length inputs, generate sizable rows representative of enterprise-scale data. Refer to the unit test for schema and example data.
 
@@ -76,7 +76,7 @@ Follow [CUDF_MICROBENCHMARKS.md](CUDF_MICROBENCHMARKS.md) to implement and run i
 ## Output
 
 Upon successful completion:
-- Benchmark utilities: `src/main/<java|scala>/com/udf/bench/BenchUtils.<java|scala>`
-- Microbenchmarks (cuDF): `src/main/<java|scala>/com/udf/bench/MicroBenchRunner.<java|scala>`
+- Benchmark utilities: `src/main/scala/com/udf/bench/BenchUtils.scala`
+- Microbenchmarks (cuDF): `src/main/scala/com/udf/bench/MicroBenchRunner.scala`
 - Generated data: `data/`
 - Benchmark results: `results/`

skills/udf-convert-to-cuda/SKILL.md

@@ -54,7 +54,7 @@ Use `src/main/java/com/udf/PlaceholderUDFNameNativeRapidsUDF.java` as a starting
 4. Implement `evaluateColumnar` to validate column count/types and call the native method.
 5. Rename the native method to a descriptive operation name, e.g. `cosineSimilarityNative`.
 
-For Scala projects, keep this Java wrapper under `src/main/java/com/udf/` and register it from the Scala test/project. JNI can be used from Scala, but the Java wrapper keeps native symbol names and examples simpler.
+The project joint-compiles Java, so keep this Java wrapper under `src/main/java/com/udf/` and register it from the Scala test. JNI can be used from Scala, but the Java wrapper keeps native symbol names and examples simpler.
 If the Java wrapper's CPU fallback needs to call a Scala object, direct references can fail before `scala-maven-plugin` compiles the Scala classes; use reflection in the row-by-row fallback only, and keep `evaluateColumnar` on the normal JNI path.
 
 Read [JNI_CUDA_GUIDE.md](references/JNI_CUDA_GUIDE.md) for the `evaluateColumnar` contract, type mapping, pointer ownership, `NativeDepsLoader`, and native memory rules.
@@ -104,16 +104,12 @@ If the build fails while resolving cuDF headers or RAPIDS CMake, check network a
 
 ## Step 5: Build and Test
 
-Fill in the target-specific TODOs in `src/test/<java|scala>/com/udf/CudfComparisonTest.<java|scala>`:
+Fill in the target-specific TODOs in `src/test/scala/com/udf/CudfComparisonTest.scala`:
 - Register `<CamelName>NativeRapidsUDF` as the GPU implementation
 - Replace placeholder UDF names
 
 Run:
 ```bash
-# Java
-mvn test -Dtest=CudfComparisonTest -Pcuda-native-udf
-
-# Scala project using a Java native RapidsUDF wrapper
 mvn test -Dsuites=com.udf.CudfComparisonTest -Pcuda-native-udf
 ```
 
@@ -129,7 +125,7 @@ docker run --rm --gpus all \
   -v /etc/group:/etc/group:ro \
   -w /workspace \
   cuda-udf-build \
-  -c "mvn -B -Dmaven.repo.local=/workspace/.m2/repository test -Dtest=CudfComparisonTest -Pcuda-native-udf -Dnative.build.path=/workspace/target/native-build-docker -DskipCudfExtraction=true"
+  -c "mvn -B -Dmaven.repo.local=/workspace/.m2/repository test -Dsuites=com.udf.CudfComparisonTest -Pcuda-native-udf -Dnative.build.path=/workspace/target/native-build-docker -DskipCudfExtraction=true"
 ```
 
 If tests fail, iterate on the Java bridge or native implementation.

skills/udf-convert-to-cudf/SKILL.md

@@ -64,16 +64,12 @@ Create a copy of the original UDF file in the same source directory (`src/main/<
 
 ## Step 3: Build and Test
 
-Fill in the target-specific TODOs in `src/test/<java|scala>/com/udf/CudfComparisonTest.<java|scala>`:
+Fill in the target-specific TODOs in `src/test/scala/com/udf/CudfComparisonTest.scala`:
 - Implement `registerRapidsUDF` to register the new RapidsUDF class.
 - Replace placeholders with the actual camel/snake UDF name
 
 Then run the test:
 ```bash
-# Java
-mvn test -Dtest=CudfComparisonTest
-
-# Scala
 mvn test -Dsuites=com.udf.CudfComparisonTest
 ```
 
@@ -91,10 +87,6 @@ Treat the unit test as the CPU behavior specification. Do not weaken or remove t
 
 Re-run with memory leak detection:
 ```bash
-# Java
-mvn test -Dtest=CudfComparisonTest -Ddebug.memory.leaks=true > /tmp/memleak.log 2>&1
-
-# Scala
 mvn test -Dsuites=com.udf.CudfComparisonTest -Ddebug.memory.leaks=true > /tmp/memleak.log 2>&1
 
 # Check for leaks

skills/udf-convert-to-sql/SKILL.md

@@ -41,16 +41,12 @@ Implement the SQL expression in a file at `src/main/resources/<snake_name>.sql`.
 
 ## Step 2: Fill in test and iterate
 
-Update `src/test/<java|scala>/com/udf/SqlComparisonTest.<java|scala>`:
+Update `src/test/scala/com/udf/SqlComparisonTest.scala`:
 - Update the SQL file path to point to your `src/main/resources/<snake_name>.sql` file
 - Replace placeholders with the actual camel/snake UDF name
 
 Then run the test:
 ```bash
-# Java
-mvn test -Dtest=SqlComparisonTest
-
-# Scala
 mvn test -Dsuites=com.udf.SqlComparisonTest
 ```
 

skills/udf-gen-test/SKILL.md

@@ -33,7 +33,7 @@ Derive `<CamelName>` and `<snake_name>` from the UDF class name.
 
 The project can be found under this skill's templates directory.
 ```bash
-cp -r templates/<java|scala> <project_root>/<CamelName>/
+cp -r templates/scala <project_root>/<CamelName>/
 ```
 
 This provides a complete Maven project with all test and benchmark infrastructure.
@@ -56,7 +56,7 @@ Set the package declaration to `com.udf`:
 
 ## Step 2: Implement the Unit Test
 
-Read `src/test/<java|scala>/com/udf/UnitTest.<java|scala>`. Replace placeholders with the actual camel/snake UDF name.
+Read `src/test/scala/com/udf/UnitTest.scala`. Replace placeholders with the actual camel/snake UDF name.
 
 Fill in the TODO methods following the docstrings. Include diverse edge cases in `createTestData` (nulls, empty strings, malformed inputs, varying lengths).
 
@@ -86,10 +86,6 @@ Assertions should verify schema, row count, deterministic ordering, output value
 ## Step 3: Compile and Test
 
 ```bash
-# Java
-mvn test -Dtest=UnitTest
-
-# Scala
 mvn test -Dsuites=com.udf.UnitTest
 ```
 
@@ -100,16 +96,16 @@ If it fails, analyze the error output (stdout/stderr) and fix the test code. Con
 The template projects use JaCoCo (Java) / scoverage (Scala) code coverage tools.
 
 ```bash
-# Java
-mvn -Pcoverage test jacoco:report -Dtest=UnitTest
+# Java UDF
+mvn -Pcoverage test jacoco:report -Dsuites=com.udf.UnitTest
 
-# Scala
+# Scala UDF
 mvn -Pcoverage scoverage:report -Dsuites=com.udf.UnitTest
 ```
 
-For Java, read `target/site/jacoco/jacoco.csv` and inspect LINE, BRANCH, and METHOD counters for the target CPU UDF class and local helper classes. In `jacoco.xml`, counters appear as `<counter type="...">` elements, and source-line misses appear under `<sourcefile><line nr="..." mi="..." ci="..." mb="..." cb="...">`.
+For a Java UDF, read `target/site/jacoco/jacoco.csv` and inspect LINE, BRANCH, and METHOD counters for the target CPU UDF class and local helper classes. In `jacoco.xml`, counters appear as `<counter type="...">` elements, and source-line misses appear under `<sourcefile><line nr="..." mi="..." ci="..." mb="..." cb="...">`.
 
-For Scala, read `target/scoverage.xml` and inspect statement, branch, and method-level coverage for the target CPU UDF class/object and local helper classes/objects. scoverage XML stores package/class/method `statement-rate` and `branch-rate` attributes, and each executable statement has `line`, `branch`, and `invocation-count` attributes.
+For a Scala UDF, read `target/scoverage.xml` and inspect statement, branch, and method-level coverage for the target CPU UDF class/object and local helper classes/objects. scoverage XML stores package/class/method `statement-rate` and `branch-rate` attributes, and each executable statement has `line`, `branch`, and `invocation-count` attributes.
 
 Use the coverage report as actionable feedback:
 1. Inspect missed Java line, branch, and method coverage, or missed Scala statement, branch, and method-level coverage.
@@ -143,6 +139,6 @@ If any quality checks fail, revise the test code and re-run.
 
 Upon successful completion:
 - Project directory: `<project_root>/<CamelName>/`
-- Unit test: `src/test/<java|scala>/com/udf/UnitTest.<java|scala>`
+- Unit test: `src/test/scala/com/udf/UnitTest.scala`
 
 These outputs are required for **Step 2: Convert UDF**.