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+/*
+ * 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.lang3.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>
+ * 
+ * <p>This class is not thread-safe</p>
+ * 
+ * @since 2.0
+ * @version $Id: StopWatch.java 1088899 2011-04-05 05:31:27Z bayard $
+ */
+public class StopWatch {
+
+    private static final long NANO_2_MILLIS = 1000000L;
+
+    // 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;
+
+    /**
+     * The start time in Millis - nanoTime is only for elapsed time so we 
+     * need to also store the currentTimeMillis to maintain the old 
+     * getStartTime API.
+     */
+    private long startTimeMillis;
+
+    /**
+     * The stop time.
+     */
+    private long stopTime;
+
+    /**
+     * <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. ");
+        }
+        this.startTime = System.nanoTime();
+        this.startTimeMillis = 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) {
+            this.stopTime = System.nanoTime();
+        }
+        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;
+    }
+
+    /**
+     * <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. ");
+        }
+        this.stopTime = System.nanoTime();
+        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. ");
+        }
+        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. ");
+        }
+        this.stopTime = System.nanoTime();
+        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. ");
+        }
+        this.startTime += (System.nanoTime() - this.stopTime);
+        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() {
+        return getNanoTime() / NANO_2_MILLIS;
+    }
+    /**
+     * <p>
+     * Get the time on the stopwatch in nanoseconds.
+     * </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 nanoseconds
+     * @since 3.0
+     */
+    public long getNanoTime() {
+        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.nanoTime() - 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() {
+        return getSplitNanoTime() / NANO_2_MILLIS;
+    }
+    /**
+     * <p>
+     * Get the split time on the stopwatch in nanoseconds.
+     * </p>
+     * 
+     * <p>
+     * This is the time between start and latest split.
+     * </p>
+     * 
+     * @return the split time in nanoseconds
+     * 
+     * @throws IllegalStateException
+     *             if the StopWatch has not yet been split.
+     * @since 3.0
+     */
+    public long getSplitNanoTime() {
+        if (this.splitState != STATE_SPLIT) {
+            throw new IllegalStateException("Stopwatch must be split to get the split time. ");
+        }
+        return this.stopTime - this.startTime;
+    }
+
+    /**
+     * Returns the time this stopwatch was started.
+     * 
+     * @return the time this stopwatch was started
+     * @throws IllegalStateException
+     *             if this StopWatch has not been started
+     * @since 2.4
+     */
+    public long getStartTime() {
+        if (this.runningState == STATE_UNSTARTED) {
+            throw new IllegalStateException("Stopwatch has not been started");
+        }
+        // System.nanoTime is for elapsed time
+        return this.startTimeMillis;
+    }
+
+    /**
+     * <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
+     */
+    @Override
+    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());
+    }
+
+}