enable maven checkstyle (#6829)

java/test/src/main/java/org/ray/api/TestProgressListener.java

@@ -9,9 +9,9 @@ import org.testng.ITestResult;
 
 public class TestProgressListener implements IInvokedMethodListener, ITestListener {
 
-  private String getFullTestName(ITestResult iTestResult) {
-    return iTestResult.getTestClass().getName() + "."
-        + iTestResult.getMethod().getMethodName();
+  private String getFullTestName(ITestResult testResult) {
+    return testResult.getTestClass().getName() + "."
+        + testResult.getMethod().getMethodName();
   }
 
   private void printInfo(String tag, String content) {

java/test/src/main/java/org/ray/api/TestUtils.java

@@ -37,10 +37,6 @@ public class TestUtils {
     skipTestIfDirectActorCallEnabled(true);
   }
 
-  public static void skipTestIfDirectActorCallDisabled() {
-    skipTestIfDirectActorCallEnabled(false);
-  }
-
   private static void skipTestIfDirectActorCallEnabled(boolean enabled) {
     if (enabled == ActorCreationOptions.DEFAULT_USE_DIRECT_CALL) {
       throw new SkipException(String.format("This test doesn't work when direct actor call is %s.",
@@ -48,6 +44,10 @@ public class TestUtils {
     }
   }
 
+  public static void skipTestIfDirectActorCallDisabled() {
+    skipTestIfDirectActorCallEnabled(false);
+  }
+
   /**
    * Wait until the given condition is met.
    *
@@ -82,7 +82,7 @@ public class TestUtils {
 
   /**
    * Warm up the cluster to make sure there's at least one idle worker.
-   *
+   * <p>
    * This is needed before calling `wait`. Because, in Travis CI, starting a new worker
    * process could be slower than the wait timeout.
    * TODO(hchen): We should consider supporting always reversing a certain number of

java/test/src/main/java/org/ray/api/test/BaseMultiLanguageTest.java

@@ -1,5 +1,8 @@
 package org.ray.api.test;
 
+import com.google.common.base.Strings;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
 import java.io.File;
 import java.lang.ProcessBuilder.Redirect;
 import java.util.List;
@@ -8,11 +11,6 @@ import java.util.Map.Entry;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
-
-import com.google.common.base.Strings;
-import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableMap;
-
 import org.ray.api.Ray;
 import org.ray.runtime.util.NetworkUtil;
 import org.slf4j.Logger;

java/test/src/main/java/org/ray/api/test/BaseTest.java

@@ -1,11 +1,9 @@
 package org.ray.api.test;
 
+import com.google.common.collect.ImmutableList;
 import java.io.File;
 import java.lang.reflect.Method;
 import java.util.List;
-
-import com.google.common.collect.ImmutableList;
-
 import org.ray.api.Ray;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

java/test/src/main/java/org/ray/api/test/SingleProcessModeTest.java

@@ -1,5 +1,9 @@
 package org.ray.api.test;
 
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 import org.ray.api.Ray;
 import org.ray.api.RayActor;
 import org.ray.api.RayObject;
@@ -9,16 +13,11 @@ import org.ray.api.id.ActorId;
 import org.testng.Assert;
 import org.testng.annotations.Test;
 
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-
 public class SingleProcessModeTest extends BaseTest {
 
-  private final static int NUM_ACTOR_INSTANCE = 10;
+  private static final int NUM_ACTOR_INSTANCE = 10;
 
-  private final static int TIMES_TO_CALL_PER_ACTOR = 10;
+  private static final int TIMES_TO_CALL_PER_ACTOR = 10;
 
   @RayRemote
   static class MyActor {

java/test/src/main/java/org/ray/api/test/UniqueIdTest.java

@@ -3,9 +3,6 @@ package org.ray.api.test;
 import java.nio.ByteBuffer;
 import java.util.Arrays;
 import javax.xml.bind.DatatypeConverter;
-
-import org.ray.api.id.ObjectId;
-import org.ray.api.id.TaskId;
 import org.ray.api.id.UniqueId;
 import org.ray.runtime.util.IdUtil;
 import org.testng.Assert;