StopWatch.java

package org.mafagafogigante.dungeon.util;

import org.mafagafogigante.dungeon.logging.DungeonLogger;

import java.util.EnumMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

/**
 * A StopWatch class used to measure time distance between two or more instants.
 *
 * <p>The precision of the measurements performed with a StopWatch are dependent on System.nanoTime() precision.
 */
public class StopWatch {

  private static final Map<TimeUnit, String> ABBREVIATIONS = new EnumMap<>(TimeUnit.class);

  static {
    ABBREVIATIONS.put(TimeUnit.NANOSECONDS, "ns");
    ABBREVIATIONS.put(TimeUnit.MICROSECONDS, "μs");
    ABBREVIATIONS.put(TimeUnit.MILLISECONDS, "ms");
    ABBREVIATIONS.put(TimeUnit.SECONDS, "s");
  }

  private final long time;

  public StopWatch() {
    time = System.nanoTime();
  }

  private long calculateTimeDifference() {
    return System.nanoTime() - time;
  }

  /**
   * Returns a String representation of the time difference between this method call and the creation of this StopWatch.
   * If the provided TimeUnit is not mapped to an abbreviation, null is returned.
   *
   * @param unit the TimeUnit to be used
   * @return a String composed of an integer followed by the abbreviation of the specified unit or null
   */
  public String toString(TimeUnit unit) {
    long timeDifference = calculateTimeDifference(); // Time difference should be calculated as soon as possible.
    if (ABBREVIATIONS.containsKey(unit)) {
      return unit.convert(timeDifference, TimeUnit.NANOSECONDS) + " " + ABBREVIATIONS.get(unit);
    } else {
      String message = "Passed a TimeUnit that does not have a defined abbreviation to StopWatch.toString(TimeUnit).";
      DungeonLogger.warning(message);
      return null;
    }
  }

  /**
   * Returns a String representation of the time difference in milliseconds between this method call and the creation of
   * this StopWatch. If the TimeUnit.MILLISECOND is not mapped to an abbreviation, null is returned.
   *
   * @return a String composed of an integer followed by the abbreviation for millisecond or null
   */
  @Override
  public String toString() {
    return toString(TimeUnit.MILLISECONDS);
  }

}