1 /*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.google.common.base;
18
19 import com.google.common.annotations.Beta;
20 import com.google.common.annotations.GwtCompatible;
21
22 /**
23 * A time source; returns a time value representing the number of nanoseconds elapsed since some
24 * fixed but arbitrary point in time. Note that most users should use {@link Stopwatch} instead of
25 * interacting with this class directly.
26 *
27 * <p><b>Warning:</b> this interface can only be used to measure elapsed time, not wall time.
28 *
29 * @author Kevin Bourrillion
30 * @since 10.0
31 * (<a href="http://code.google.com/p/guava-libraries/wiki/Compatibility"
32 * >mostly source-compatible</a> since 9.0)
33 */
34 @Beta
35 @GwtCompatible
36 public abstract class Ticker {
37 /**
38 * Constructor for use by subclasses.
39 */
40 protected Ticker() {}
41
42 /**
43 * Returns the number of nanoseconds elapsed since this ticker's fixed
44 * point of reference.
45 */
46 public abstract long read();
47
48 /**
49 * A ticker that reads the current time using {@link System#nanoTime}.
50 *
51 * @since 10.0
52 */
53 public static Ticker systemTicker() {
54 return SYSTEM_TICKER;
55 }
56
57 private static final Ticker SYSTEM_TICKER = new Ticker() {
58 @Override
59 public long read() {
60 return Platform.systemNanoTime();
61 }
62 };
63 }