[java] Improve UniqueID code. (#2723)

java/runtime-common/src/main/java/org/ray/core/RayRuntime.java

@@ -209,7 +209,7 @@ public abstract class RayRuntime implements RayApi {
   }
 
   /**
-   * get the task identity of the currently running task, UniqueID.Nil if not inside any
+   * get the task identity of the currently running task, UniqueID.NIL if not inside any
    */
   public UniqueID getCurrentTaskId() {
     return worker.getCurrentTaskId();
@@ -381,7 +381,7 @@ public abstract class RayRuntime implements RayApi {
   }
 
   /**
-   * get the object put identity of the currently running task, UniqueID.Nil if not inside any
+   * get the object put identity of the currently running task, UniqueID.NIL if not inside any
    */
   public UniqueID[] getCurrentTaskReturnIDs() {
     return worker.getCurrentTaskReturnIDs();

java/runtime-common/src/main/java/org/ray/core/Worker.java

@@ -67,9 +67,8 @@ public class Worker {
 
   }
 
-
   private RayObject taskSubmit(UniqueID taskId, MethodId methodId, Object[] args) {
-    RayInvocation ri = createRemoteInvocation(methodId, args, RayActor.nil);
+    RayInvocation ri = createRemoteInvocation(methodId, args, RayActor.NIL);
     return scheduler.submit(taskId, ri);
   }
 
@@ -95,7 +94,7 @@ public class Worker {
       RayFunc func, Object[] args) {
     Preconditions.checkNotNull(taskId);
     MethodId mid = methodIdOf(func);
-    RayInvocation ri = createRemoteInvocation(mid, args, RayActor.nil);
+    RayInvocation ri = createRemoteInvocation(mid, args, RayActor.NIL);
     return scheduler.submitActorCreationTask(taskId, createActorId, ri);
   }
 

java/runtime-common/src/main/java/org/ray/core/WorkerContext.java

@@ -35,13 +35,13 @@ public class WorkerContext {
     currentWorkerCtx.set(ctx);
 
     TaskSpec dummy = new TaskSpec();
-    dummy.parentTaskId = UniqueID.nil;
+    dummy.parentTaskId = UniqueID.NIL;
     if (params.worker_mode == WorkerMode.DRIVER) {
       dummy.taskId = UniqueID.randomId();
     } else {
-      dummy.taskId = UniqueID.nil;
+      dummy.taskId = UniqueID.NIL;
     }
-    dummy.actorId = UniqueID.nil;
+    dummy.actorId = UniqueID.NIL;
     dummy.driverId = params.driver_id;
     prepare(dummy, null);
 

java/runtime-common/src/main/java/org/ray/core/model/RayParameters.java

@@ -44,7 +44,7 @@ public class RayParameters {
   public int local_scheduler_rpc_port = 34567;
 
   @AConfig(comment = "driver ID when the worker is served as a driver")
-  public UniqueID driver_id = UniqueID.nil;
+  public UniqueID driver_id = UniqueID.NIL;
 
   @AConfig(comment = "logging directory")
   public String log_dir = "/tmp/raylogs";

java/runtime-common/src/main/java/org/ray/spi/LocalSchedulerProxy.java

@@ -28,14 +28,14 @@ public class LocalSchedulerProxy {
 
   public RayObject submit(UniqueID taskId, RayInvocation invocation) {
     UniqueID[] returnIds = genReturnIds(taskId, 1);
-    this.doSubmit(invocation, taskId, returnIds, UniqueID.nil);
+    this.doSubmit(invocation, taskId, returnIds, UniqueID.NIL);
     return new RayObject(returnIds[0]);
   }
 
   public RayObject submitActorTask(UniqueID taskId, RayInvocation invocation) {
     // add one for the dummy return ID
     UniqueID[] returnIds = genReturnIds(taskId, 2);
-    this.doSubmit(invocation, taskId, returnIds, UniqueID.nil);
+    this.doSubmit(invocation, taskId, returnIds, UniqueID.NIL);
     return new RayObject(returnIds[0]);
   }
 

java/runtime-common/src/main/java/org/ray/spi/model/RayInvocation.java

@@ -9,7 +9,7 @@ import org.ray.api.UniqueID;
  */
 public class RayInvocation {
 
-  private static final RayActor<?> nil = new RayActor<>(UniqueID.nil, UniqueID.nil);
+  private static final RayActor<?> nil = new RayActor<>(UniqueID.NIL, UniqueID.NIL);
   public final String className;
   /**
    * unique id for a method.