code: package io.ray.api.id;
  
  import java.io.Serializable;
  import java.nio.ByteBuffer;
  import java.util.Arrays;
  import java.util.Random;
  
  /** Represents the id of a placement group. */
  public class PlacementGroupId extends BaseId implements Serializable {
  
    private static final int UNIQUE_BYTES_LENGTH = 14;
  
    public static final int LENGTH = JobId.LENGTH + UNIQUE_BYTES_LENGTH;
  
    public static final PlacementGroupId NIL = nil();
  
    private PlacementGroupId(byte[] id) {
      super(id);
    }
  
    /** Creates a PlacementGroupId from the given ByteBuffer. */
    public static PlacementGroupId fromByteBuffer(ByteBuffer bb) {
      return new PlacementGroupId(byteBuffer2Bytes(bb));
    }
  
    /** Create a PlacementGroupId instance according to the given bytes. */
    public static PlacementGroupId fromBytes(byte[] bytes) {
      return new PlacementGroupId(bytes);
    }
  
    /** Generate a nil PlacementGroupId. */
    private static PlacementGroupId nil() {
      byte[] b = new byte[LENGTH];
      Arrays.fill(b, (byte) 0xFF);
      return new PlacementGroupId(b);
    }
  
    /** Generate an PlacementGroupId with random value. Used for local mode and test only. */
    public static PlacementGroupId fromRandom() {
      byte[] b = new byte[LENGTH];
      new Random().nextBytes(b);
      return new PlacementGroupId(b);
    }
  
    @Override
    public int size() {
      return LENGTH;
    }
  }
  