code: package io.ray.runtime.util;
  
  import io.ray.api.id.ActorId;
  import io.ray.api.id.ObjectId;
  import io.ray.api.id.TaskId;
  import java.util.Arrays;
  
  /**
   * Helper method for different Ids. Note: any changes to these methods must be synced with C++
   * helper functions in src/ray/common/id.h
   */
  public class IdUtil {
  
    /**
     * Compute the actor ID of the task which created this object.
     *
     * @return The actor ID of the task which created this object.
     */
    public static ActorId getActorIdFromObjectId(ObjectId objectId) {
      byte[] taskIdBytes = new byte[TaskId.LENGTH];
      System.arraycopy(objectId.getBytes(), 0, taskIdBytes, 0, TaskId.LENGTH);
      TaskId taskId = TaskId.fromBytes(taskIdBytes);
      byte[] actorIdBytes = new byte[ActorId.LENGTH];
      System.arraycopy(
          taskId.getBytes(), TaskId.UNIQUE_BYTES_LENGTH, actorIdBytes, 0, ActorId.LENGTH);
      return ActorId.fromBytes(actorIdBytes);
    }
  
    /** Compute the dummy object id for actor creation task. */
    public static ObjectId getActorCreationDummyObjectId(ActorId actorId) {
      byte[] objectIdBytes = new byte[ObjectId.LENGTH];
      Arrays.fill(objectIdBytes, (byte) 0xFF);
      byte[] actorIdBytes = actorId.getBytes();
      System.arraycopy(actorIdBytes, 0, objectIdBytes, 0, ActorId.LENGTH);
      return new ObjectId(objectIdBytes);
    }
  }
  