Add initial JVM example.

Author: stuhood

.github/workflows/pants.yaml

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+# Copyright 2021 Pants project contributors.
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+# See https://pants.readme.io/docs/using-pants-in-ci for tips on how to set up your CI with Pants.
+
+name: Pants
+
+on: [push, pull_request]
+
+jobs:
+  org-check:
+    name: Check GitHub Organization
+    if: ${{ github.repository_owner == 'pantsbuild' }}
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Noop
+        run: "true"
+  build:
+    name: Perform CI Checks
+    needs: org-check
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/cache@v2
+      id: cache
+      with:
+        path: |
+          ~/.cache/pants/setup
+          ~/.cache/pants/lmdb_store
+          ~/.cache/pants/named_caches
+        key: ${{ runner.os }}-
+    - name: Bootstrap Pants
+      run: ./pants --version
+    - name: Check Pants config files
+      run: ./pants tailor --check update-build-files --check
+    - name: Lint, compile, and test
+      run: ./pants lint check test '::'
+    - name: Package / Run
+      run: |
+        ./pants package ::
+    - name: Upload Pants log
+      uses: actions/upload-artifact@v2
+      with:
+        name: pants-log
+        path: .pants.d/pants.log
+      if: always()  # We want the log even on failures.

.gitignore

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+# Pants workspace files
+/.pants.d/
+/dist/
+/.pids
+/.pants.workdir.file_lock*
+
+# Editor specific files
+*.swp

.scalafmt.conf

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+version = 3.2.1
+runner.dialect = scala213
+maxColumn = 100

3rdparty/jvm/com/google/guava/BUILD

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+jvm_artifact(
+    group="com.google.guava",
+    artifact="guava",
+    version="31.0.1-jre",
+    # Because `guava` provides a package which does not match its `group`, we explicitly list it
+    # here, which allows inference to recognize that imports of this package are provided by this
+    # artifact. See https://www.pantsbuild.org/v2.9/docs/reference-jvm_artifact#codepackagescode
+    # for more information.
+    packages=["com.google.common.**"],
+)

3rdparty/jvm/com/lihaoyi/BUILD

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+jvm_artifact(
+    name="acyclic",
+    group="com.lihaoyi",
+    artifact="acyclic_2.13",
+    version="0.2.1",
+    # Because `acyclic` provides a package which does not match its `group`, we explicitly list it
+    # here, which allows inference to recognize that imports of this package are provided by this
+    # artifact. See https://www.pantsbuild.org/v2.9/docs/reference-jvm_artifact#codepackagescode
+    # for more information.
+    packages=["acyclic.**"],
+)