[Java] lint unused imports (#4100)

java/api/src/main/java/org/ray/api/options/ActorCreationOptions.java

@@ -1,6 +1,5 @@
 package org.ray.api.options;
 
-import java.util.HashMap;
 import java.util.Map;
 
 /**

java/api/src/main/java/org/ray/api/runtime/RayRuntime.java

@@ -7,7 +7,6 @@ import org.ray.api.WaitResult;
 import org.ray.api.function.RayFunc;
 import org.ray.api.id.UniqueId;
 import org.ray.api.options.ActorCreationOptions;
-import org.ray.api.options.BaseTaskOptions;
 import org.ray.api.options.CallOptions;
 
 /**

java/checkstyle.xml

@@ -28,6 +28,9 @@
     </module>
 
     <module name="TreeWalker">
+        <!-- Below are custom config items in addition to the original google style config. -->
+        <module name="UnusedImports"/>
+        <!-- End of custom config items -->
         <module name="OuterTypeFilename"/>
         <module name="IllegalTokenText">
             <property name="tokens" value="STRING_LITERAL, CHAR_LITERAL"/>

java/runtime/src/main/java/org/ray/runtime/AbstractRayRuntime.java

@@ -1,7 +1,5 @@
 package org.ray.runtime;
 
-import static java.util.stream.Collectors.toList;
-
 import com.google.common.collect.ImmutableList;
 import java.util.ArrayList;
 import java.util.Arrays;

java/runtime/src/main/java/org/ray/runtime/objectstore/ObjectStoreProxy.java

@@ -8,10 +8,8 @@ import org.apache.arrow.plasma.ObjectStoreLink;
 import org.apache.arrow.plasma.ObjectStoreLink.ObjectStoreData;
 import org.apache.arrow.plasma.PlasmaClient;
 import org.apache.arrow.plasma.exceptions.DuplicateObjectException;
-import org.apache.commons.lang3.tuple.Pair;
 import org.ray.api.exception.RayActorException;
 import org.ray.api.exception.RayException;
-import org.ray.api.exception.RayTaskException;
 import org.ray.api.exception.RayWorkerException;
 import org.ray.api.exception.UnreconstructableException;
 import org.ray.api.id.UniqueId;

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

@@ -1,6 +1,5 @@
 package org.ray.api.test;
 
-import java.io.File;
 import org.ray.api.Ray;
 import org.testng.annotations.AfterMethod;
 import org.testng.annotations.BeforeMethod;

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

@@ -2,7 +2,6 @@ package org.ray.api.test;
 
 import com.google.common.collect.ImmutableList;
 import java.io.File;
-import java.io.IOException;
 import java.lang.ProcessBuilder.Redirect;
 import java.util.List;
 import java.util.concurrent.TimeUnit;

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

@@ -8,7 +8,6 @@ import org.ray.api.RayObject;
 import org.ray.api.annotation.RayRemote;
 import org.ray.runtime.util.FileUtil;
 import org.testng.Assert;
-import org.testng.annotations.Test;
 
 /**
  * given a directory of document files on each "machine", we would like to count the appearance of