[Java] Throw exception if Ray.init() is not called and users try to access ray API (#10497)

java/test/src/main/java/io/ray/test/BaseMultiLanguageTest.java

@@ -91,7 +91,7 @@ public abstract class BaseMultiLanguageTest {
     }
 
     // Connect to the cluster.
-    Assert.assertNull(Ray.internal());
+    Assert.assertFalse(Ray.isInitialized());
     System.setProperty("ray.redis.address", "127.0.0.1:6379");
     System.setProperty("ray.object-store.socket-name", PLASMA_STORE_SOCKET_NAME);
     System.setProperty("ray.raylet.socket-name", RAYLET_SOCKET_NAME);

java/test/src/main/java/io/ray/test/BaseTest.java

@@ -19,7 +19,7 @@ public class BaseTest {
 
   @BeforeMethod(alwaysRun = true)
   public void setUpBase(Method method) {
-    Assert.assertNull(Ray.internal());
+    Assert.assertFalse(Ray.isInitialized());
     Ray.init();
     // These files need to be deleted after each test case.
     filesToDelete = ImmutableList.of(