Android中Log的输出有如下几种：
Log.v(String tag, String msg); //VERBOSE
Log.d(String tag, String msg); //DEBUG
Log.i(String tag, String msg); //INFO
Log.w(String tag, String msg); //WARN
Log.e(String tag, String msg); //ERROR
以上log的级别依次升高，VERBOSE DEBUG信息应当只存在于开发中，INFO,WARN，ERROR这三种log将出现在发布版本中。
对于JAVA类中，可以声明一个字符串常量TAG，Logcat可以根据他来区分不同的log,例如在WindowsManagerService.java的类中，定义如下所示：
static final Sting TAG = "WindowManager"
需要打log的地方
Log.v(TAG, "Figuring out where to add app window" + client.asBinder() + "(token=" + token + ")");
logcat使用方法如下所示:
logcat [options] [filterspecs]
option "-s" 用来设置过滤器，格式是这样的 <tag>[:priority]
其中 <tag> 表示log的component， tag (或者使用 * 表示所有) ，priority如下所示:
V Verbose
D Debug
I Info
W Warn
E Error
F Fatal
S Silent
例：
logcat -s *:s 不打任何log
logcat -s WindowMnager:V <-- 打印WindowManagerService 中 Verbose 信息
如果在eclipse中查看Android log 输出，也就是logcat信息，可以 选择Windows > Show View > Other... > Android > LogCat。
附
logcat的参数说明:
Usage: logcat [options] [filterspecs]
options include:
-s Set default filter to silent.
Like specifying filterspec '*:s'
-f <filename> Log to file. Default to stdout
-r [<kbytes>] Rotate log every kbytes. (16 if unspecified). Requires -f
-n <count> Sets max number of rotated logs to <count>, default 4
-v <format> Sets the log print format, where <format> is one of:
brief process tag thread raw time long
-c clear (flush) the entire log and exit
-d dump the log and then exit (don't block)
-g get the size of the log's ring buffer and exit
-b <buffer> request alternate ring buffer, defaults to 'main'
filterspecs are a series of
<tag>[:priority]
where <tag> is a log component tag (or * for all) and priority is:
V Verbose
D Debug
I Info
W Warn
E Error
F Fatal
S Silent (supress all output)
'*' means '*:d' and <tag> by itself means <tag>:v
If not specified on the commandline, filterspec is set from ANDROID_LOG_TAG
If no filterspec is found, filter defaults to '*:I'
If not specified with -v, format is set from ANDROID_PRINTF_LOG
or defaults to "brief"