@ElementTypesAreNonnullByDefault
public abstract class Ticker {
  /** Constructor for use by subclasses. */
  protected Ticker() {}

  /** Returns the number of nanoseconds elapsed since this ticker's fixed point of reference. */
  public abstract long read();

  /**
   * A ticker that reads the current time using {@link System#nanoTime}.
   *
   * @since 10.0
   */
  public static Ticker systemTicker() {
    return SYSTEM_TICKER;
  }

@ElementTypesAreNonnullByDefault
public abstract class Ticker {
  /** Constructor for use by subclasses. */
  protected Ticker() {}

  /** Returns the number of nanoseconds elapsed since this ticker's fixed point of reference. */
  public abstract long read();

  /**
   * A ticker that reads the current time using {@link System#nanoTime}.
   *
   * @since 10.0
   */
  public static Ticker systemTicker() {
    return SYSTEM_TICKER;
  }