001 /*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.base;
018
019 import com.google.common.annotations.Beta;
020 import com.google.common.annotations.GwtCompatible;
021
022 /**
023 * A time source; returns a time value representing the number of nanoseconds elapsed since some
024 * fixed but arbitrary point in time. Note that most users should use {@link Stopwatch} instead of
025 * interacting with this class directly.
026 *
027 * <p><b>Warning:</b> this interface can only be used to measure elapsed time, not wall time.
028 *
029 * @author Kevin Bourrillion
030 * @since 10.0
031 * (<a href="http://code.google.com/p/guava-libraries/wiki/Compatibility"
032 * >mostly source-compatible</a> since 9.0)
033 */
034 @Beta
035 @GwtCompatible
036 public abstract class Ticker {
037 /**
038 * Constructor for use by subclasses.
039 */
040 protected Ticker() {}
041
042 /**
043 * Returns the number of nanoseconds elapsed since this ticker's fixed
044 * point of reference.
045 */
046 public abstract long read();
047
048 /**
049 * A ticker that reads the current time using {@link System#nanoTime}.
050 *
051 * @since 10.0
052 */
053 public static Ticker systemTicker() {
054 return SYSTEM_TICKER;
055 }
056
057 private static final Ticker SYSTEM_TICKER = new Ticker() {
058 @Override
059 public long read() {
060 return Platform.systemNanoTime();
061 }
062 };
063 }