Android
android.util
public final class

android.util.Log

java.lang.Object
android.util.Log

API for sending log output.

Generally, use the Log.v() Log.d() Log.i() Log.w() and Log.e() methods.

The order in terms of verbosity, from least to most is ERROR, WARN, INFO, DEBUG, VERBOSE. Verbose should never be compiled into an application except during development. Debug logs are compiled in but stripped at runtime. Error, warning and info logs are always kept.

Tip: A good convention is to declare a TAG constant in your class:

private static final String TAG = "MyActivity";
and use that in subsequent calls to the log methods.

Tip: Don't forget that when you make a call like

Log.v(TAG, "index=" + i);
that when you're building the string to pass into Log.d, Java uses a StringBuilder and at least three allocations occur: the StringBuilder itself, the buffer, and the String object. Realistically, there is also another buffer allocation and copy, and even more pressure on the gc. That means that if your log message is filtered out, you might be doing significant work and incurring significant overhead.

Summary

Constants

      Value  
int  ASSERT  Priority constant for the println method.  0x00000007 
int  DEBUG  Priority constant for the println method; use Log.d.  0x00000003 
int  ERROR  Priority constant for the println method; use Log.e.  0x00000006 
int  INFO  Priority constant for the println method; use Log.i.  0x00000004 
int  VERBOSE  Priority constant for the println method; use Log.v.  0x00000002 
int  WARN  Priority constant for the println method; use Log.w.  0x00000005 

Public Methods

      static    int  d(String tag, String msg, Throwable tr)
Send a DEBUG log message and log the exception.
      static    int  d(String tag, String msg)
Send a DEBUG log message.
      static    int  e(String tag, String msg)
Send an ERROR log message.
      static    int  e(String tag, String msg, Throwable tr)
Send a ERROR log message and log the exception.
      static    String  getStackTraceString(Throwable tr)
Handy function to get a loggable stack trace from a Throwable
      static    int  i(String tag, String msg, Throwable tr)
Send a INFO log message and log the exception.
      static    int  i(String tag, String msg)
Send an INFO log message.
      static    boolean  isLoggable(String tag, int level)
Checks to see whether or not a log for the specified tag is loggable at the specified level.
      static    int  println(int priority, String tag, String msg)
Low-level logging call.
      static    int  v(String tag, String msg, Throwable tr)
Send a VERBOSE log message and log the exception.
      static    int  v(String tag, String msg)
Send a VERBOSE log message.
      static    int  w(String tag, String msg)
Send a WARN log message.
      static    int  w(String tag, Throwable tr)
      static    int  w(String tag, String msg, Throwable tr)
Send a WARN log message and log the exception.
Methods inherited from class java.lang.Object

Details

Constants

public static final int ASSERT

Priority constant for the println method.
Constant Value: 7 (0x00000007)

public static final int DEBUG

Priority constant for the println method; use Log.d.
Constant Value: 3 (0x00000003)

public static final int ERROR

Priority constant for the println method; use Log.e.
Constant Value: 6 (0x00000006)

public static final int INFO

Priority constant for the println method; use Log.i.
Constant Value: 4 (0x00000004)

public static final int VERBOSE

Priority constant for the println method; use Log.v.
Constant Value: 2 (0x00000002)

public static final int WARN

Priority constant for the println method; use Log.w.
Constant Value: 5 (0x00000005)

Public Methods

public static int d(String tag, String msg, Throwable tr)

Send a DEBUG log message and log the exception.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.
tr An exception to log

public static int d(String tag, String msg)

Send a DEBUG log message.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.

public static int e(String tag, String msg)

Send an ERROR log message.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.

public static int e(String tag, String msg, Throwable tr)

Send a ERROR log message and log the exception.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.
tr An exception to log

public static String getStackTraceString(Throwable tr)

Handy function to get a loggable stack trace from a Throwable

Parameters

tr An exception to log

public static int i(String tag, String msg, Throwable tr)

Send a INFO log message and log the exception.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.
tr An exception to log

public static int i(String tag, String msg)

Send an INFO log message.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.

public static boolean isLoggable(String tag, int level)

Checks to see whether or not a log for the specified tag is loggable at the specified level. The default level of any tag is set to INFO. This means that any level above and including INFO will be logged. Before you make any calls to a logging method you should check to see if your tag should be logged. You can change the default level by setting a system property: 'setprop log.tag.<YOUR_LOG_TAG> <LEVEL>' Where level is either VERBOSE, DEBUG, INFO, WARN, ERROR, ASSERT, or SUPPRESS. SUPRESS will turn off all logging for your tag. You can also create a local.prop file that with the following in it: 'log.tag.<YOUR_LOG_TAG>=<LEVEL>' and place that in /data/local.prop.

Parameters

tag The tag to check.
level The level to check.

Returns

  • Whether or not that this is allowed to be logged.

Throws

IllegalArgumentException is thrown if the tag.length() > 23.

public static int println(int priority, String tag, String msg)

Low-level logging call.

Parameters

priority The priority/type of this log message
tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.

Returns

  • The number of bytes written.

public static int v(String tag, String msg, Throwable tr)

Send a VERBOSE log message and log the exception.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.
tr An exception to log

public static int v(String tag, String msg)

Send a VERBOSE log message.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.

public static int w(String tag, String msg)

Send a WARN log message.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.

public static int w(String tag, Throwable tr)

public static int w(String tag, String msg, Throwable tr)

Send a WARN log message and log the exception.

Parameters

tag Used to identify the source of a log message. It usually identfies the class or activity where the log call occurs.
msg The message you would like logged.
tr An exception to log
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