add build action

.github/workflows/build.yml

@@ -0,0 +1,16 @@
+name: Build
+
+on: [push]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+      - name: Set up JDK 12
+        uses: actions/setup-java@v1
+        with:
+          java-version: 12
+      - run: find . -type f -name "*.java" > sources.txt
+      - run: javac @sources.txt