Update workflow.yml

Author: LorenzBuehmann

.github/workflows/workflow.yml

@@ -8,14 +8,20 @@ on:
 
 jobs:
   build:
-
-    runs-on: ubuntu-latest
+    name: Build on Java ${{ matrix.java_version }} and ${{ matrix.os }}
+    strategy:
+      matrix:
+        java_version: ['1.8', '9.0.x', '12.0.2']
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+    
+    runs-on: ${{ matrix.os }}
 
     steps:
     - uses: actions/checkout@v1
-    - name: Set up JDK 1.8
+    - name: Set up JDK ${{ matrix.java_version }}
       uses: actions/setup-java@v1
       with:
-        java-version: 1.8
+        java-version: ${{ matrix.java_version }}
+        architecture: x64
     - name: Build with Maven
       run: mvn package --file pom.xml