code: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   * 
   *      http://www.apache.org/licenses/LICENSE-2.0
   * 
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.lang.time;
  
  /**
   * <p><code>StopWatch</code> provides a convenient API for timings.</p>
   * 
   * <p>To start the watch, call {@link #start()}. At this point you can:</p>
   * <ul>
   *  <li>{@link #split()} the watch to get the time whilst the watch continues in the
   *   background. {@link #unsplit()} will remove the effect of the split. At this point,
   *   these three options are available again.</li>
   *  <li>{@link #suspend()} the watch to pause it. {@link #resume()} allows the watch
   *   to continue. Any time between the suspend and resume will not be counted in
   *   the total. At this point, these three options are available again.</li>
   *  <li>{@link #stop()} the watch to complete the timing session.</li>
   * </ul>
   *
   * <p>It is intended that the output methods {@link #toString()} and {@link #getTime()}
   * should only be called after stop, split or suspend, however a suitable result will
   * be returned at other points.</p>
   *
   * <p>NOTE: As from v2.1, the methods protect against inappropriate calls.
   * Thus you cannot now call stop before start, resume before suspend or
   * unsplit before split.</p>
   *
   * <p>1. split(), suspend(), or stop() cannot be invoked twice<br />
   * 2. unsplit() may only be called if the watch has been split()<br />
   * 3. resume() may only be called if the watch has been suspend()<br />
   * 4. start() cannot be called twice without calling reset()</p>
   *
   * @author Stephen Colebourne
   * @since 2.0
   * @version $Id: StopWatch.java 504351 2007-02-06 22:49:50Z bayard $
   */
  public class StopWatch {
  
      // running states
      private static final int STATE_UNSTARTED = 0;
      private static final int STATE_RUNNING   = 1;
      private static final int STATE_STOPPED   = 2;
      private static final int STATE_SUSPENDED = 3;
  
      // split state
      private static final int STATE_UNSPLIT = 10;
      private static final int STATE_SPLIT   = 11;
  
      /**
       *  The current running state of the StopWatch. 
       */
      private int runningState = STATE_UNSTARTED;
  
      /**
       * Whether the stopwatch has a split time recorded. 
       */
      private int splitState   = STATE_UNSPLIT;
  
      /**
       * The start time.
       */
      private long startTime = -1;
      /**
       * The stop time.
       */
      private long stopTime = -1;
  
      /**
       * <p>Constructor.</p>
       */
      public StopWatch() {
          super();
      }
  
      /**
       * <p>Start the stopwatch.</p>
       * 
       * <p>This method starts a new timing session, clearing any previous values.</p>
       *
       * @throws IllegalStateException if the StopWatch is already running.
       */
      public void start() {
          if(this.runningState == STATE_STOPPED) {
              throw new IllegalStateException("Stopwatch must be reset before being restarted. ");
          }
          if(this.runningState != STATE_UNSTARTED) {
              throw new IllegalStateException("Stopwatch already started. ");
          }
          stopTime = -1;
          startTime = System.currentTimeMillis();
          this.runningState = STATE_RUNNING;
      }
  
      /**
       * <p>Stop the stopwatch.</p>
       * 
       * <p>This method ends a new timing session, allowing the time to be retrieved.</p>
       *
       * @throws IllegalStateException if the StopWatch is not running.
       */
      public void stop() {
          if(this.runningState != STATE_RUNNING && this.runningState != STATE_SUSPENDED) {
              throw new IllegalStateException("Stopwatch is not running. ");
          }
          if(this.runningState == STATE_RUNNING) {
              stopTime = System.currentTimeMillis();
          }
          this.runningState = STATE_STOPPED;
      }
  
      /**
       * <p>Resets the stopwatch. Stops it if need be. </p>
       * 
       * <p>This method clears the internal values to allow the object to be reused.</p>
       */
      public void reset() {
          this.runningState = STATE_UNSTARTED;
          this.splitState   = STATE_UNSPLIT;
          startTime = -1;
          stopTime = -1;
      }
  
      /**
       * <p>Split the time.</p>
       * 
       * <p>This method sets the stop time of the watch to allow a time to be extracted.
       * The start time is unaffected, enabling {@link #unsplit()} to continue the 
       * timing from the original start point.</p>
       *
       * @throws IllegalStateException if the StopWatch is not running.
       */
      public void split() {
          if(this.runningState != STATE_RUNNING) {
              throw new IllegalStateException("Stopwatch is not running. ");
          }
          stopTime = System.currentTimeMillis();
          this.splitState = STATE_SPLIT;
      }
  
      /**
       * <p>Remove a split.</p>
       * 
       * <p>This method clears the stop time. The start time is unaffected, enabling 
       * timing from the original start point to continue.</p>
       *
       * @throws IllegalStateException if the StopWatch has not been split.
       */
      public void unsplit() {
          if(this.splitState != STATE_SPLIT) {
              throw new IllegalStateException("Stopwatch has not been split. ");
          }
          stopTime = -1;
          this.splitState = STATE_UNSPLIT;
      }
  
      /**
       * <p>Suspend the stopwatch for later resumption.</p>
       * 
       * <p>This method suspends the watch until it is resumed. The watch will not include
       * time between the suspend and resume calls in the total time.</p>
       *
       * @throws IllegalStateException if the StopWatch is not currently running.
       */
      public void suspend() {
          if(this.runningState != STATE_RUNNING) {
              throw new IllegalStateException("Stopwatch must be running to suspend. ");
          }
          stopTime = System.currentTimeMillis();
          this.runningState = STATE_SUSPENDED;
      }
  
      /**
       * <p>Resume the stopwatch after a suspend.</p>
       * 
       * <p>This method resumes the watch after it was suspended. The watch will not include
       * time between the suspend and resume calls in the total time.</p>
       *
       * @throws IllegalStateException if the StopWatch has not been suspended. 
       */
      public void resume() {
          if(this.runningState != STATE_SUSPENDED) {
              throw new IllegalStateException("Stopwatch must be suspended to resume. ");
          }
          startTime += (System.currentTimeMillis() - stopTime);
          stopTime = -1;
          this.runningState = STATE_RUNNING;
      }
  
      /**
       * <p>Get the time on the stopwatch.</p>
       * 
       * <p>This is either the time between the start and the moment this method 
       * is called, or the amount of time between start and stop.</p>
       * 
       * @return the time in milliseconds
       */
      public long getTime() {
          if(this.runningState == STATE_STOPPED || this.runningState == STATE_SUSPENDED) {
              return this.stopTime - this.startTime;
          } else
          if(this.runningState == STATE_UNSTARTED) {
              return 0;
          } else
          if(this.runningState == STATE_RUNNING) {
              return System.currentTimeMillis() - this.startTime;
          }
          throw new RuntimeException("Illegal running state has occured. ");
      }
  
      /**
       * <p>Get the split time on the stopwatch.</p>
       * 
       * <p>This is the time between start and latest split. </p>
       * 
       * @return the split time in milliseconds
       *
       * @throws IllegalStateException if the StopWatch has not yet been split.
       * @since 2.1
       */
      public long getSplitTime() {
          if(this.splitState != STATE_SPLIT) {
              throw new IllegalStateException("Stopwatch must be split to get the split time. ");
          }
          return this.stopTime - this.startTime;
      }
  
      /**
       * <p>Gets a summary of the time that the stopwatch recorded as a string.</p>
       * 
       * <p>The format used is ISO8601-like,
       * <i>hours</i>:<i>minutes</i>:<i>seconds</i>.<i>milliseconds</i>.</p>
       * 
       * @return the time as a String
       */
      public String toString() {
          return DurationFormatUtils.formatDurationHMS(getTime());
      }
  
      /**
       * <p>Gets a summary of the split time that the stopwatch recorded as a string.</p>
       * 
       * <p>The format used is ISO8601-like,
       * <i>hours</i>:<i>minutes</i>:<i>seconds</i>.<i>milliseconds</i>.</p>
       * 
       * @return the split time as a String
       * @since 2.1
       */
      public String toSplitString() {
          return DurationFormatUtils.formatDurationHMS(getSplitTime());
      }
  
  }
  