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