Added in API level 1

Summary: Constants | Methods | Inherited Methods

Log

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Kotlin |Java

public final class Log
extends Object

java.lang.Object
↳	android.util.Log

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API for sending log output.

Generally, you should use the Log.v(), Log.d(), Log.i(), Log.w(), and Log.e() methods to write logs. You can then view the logs in logcat.

The order in terms of verbosity, from least to most is ERROR, WARN, INFO, DEBUG, VERBOSE.

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, the compiler 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.

When calling the log methods that take a Throwable parameter, if any of the throwables in the cause chain is an UnknownHostException, then the stack trace is not logged.

Note: The return value from the logging functions in this class may vary between Android releases due to changes in the logging implementation. For the methods that return an integer, a positive value may be considered as a successful invocation.

Summary

Constants
int	ASSERT Priority constant for the println method.
int	DEBUG Priority constant for the println method; use Log.d.
int	ERROR Priority constant for the println method; use Log.e.
int	INFO Priority constant for the println method; use Log.i.
int	VERBOSE Priority constant for the println method; use Log.v.
int	WARN Priority constant for the println method; use Log.w.

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 If any of the throwables in the cause chain is an UnknownHostException, this returns an empty string.
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) Send a VERBOSE log message.
static int	v(String tag, String msg, Throwable tr) Send a VERBOSE log message and log the exception.
static int	w(String tag, Throwable tr) Send a WARN log message and log the exception.
static int	w(String tag, String msg, Throwable tr) Send a WARN log message and log the exception.
static int	w(String tag, String msg) Send a WARN log message.
static int	wtf(String tag, String msg) What a Terrible Failure: Report a condition that should never happen.
static int	wtf(String tag, Throwable tr) What a Terrible Failure: Report an exception that should never happen.
static int	wtf(String tag, String msg, Throwable tr) What a Terrible Failure: Report an exception that should never happen.

Inherited methods

From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. final void wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Constants

ASSERT

Added in API level 1

public static final int ASSERT

Priority constant for the println method.

Constant Value: 7 (0x00000007)

DEBUG

Added in API level 1

public static final int DEBUG

Priority constant for the println method; use Log.d.

Constant Value: 3 (0x00000003)

ERROR

Added in API level 1

public static final int ERROR

Priority constant for the println method; use Log.e.

Constant Value: 6 (0x00000006)

INFO

Added in API level 1

public static final int INFO

Priority constant for the println method; use Log.i.

Constant Value: 4 (0x00000004)

VERBOSE

Added in API level 1

public static final int VERBOSE

Priority constant for the println method; use Log.v.

Constant Value: 2 (0x00000002)

WARN

Added in API level 1

public static final int WARN

Priority constant for the println method; use Log.w.

Constant Value: 5 (0x00000005)

Public methods

d

Added in API level 1

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

Send a DEBUG log message and log the exception.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value may be null.
tr	Throwable: An exception to log. This value may be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

d

Added in API level 1

public static int d (String tag, 
                String msg)

Send a DEBUG log message.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value cannot be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

e

Added in API level 1

public static int e (String tag, 
                String msg)

Send an ERROR log message.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value cannot be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

e

Added in API level 1

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

Send a ERROR log message and log the exception.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value may be null.
tr	Throwable: An exception to log. This value may be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

getStackTraceString

Added in API level 1

public static String getStackTraceString (Throwable tr)

Handy function to get a loggable stack trace from a Throwable

If any of the throwables in the cause chain is an UnknownHostException, this returns an empty string.

Parameters
tr	Throwable: An exception to log. This value may be null.

Returns
String	This value cannot be null.

i

Added in API level 1

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

Send a INFO log message and log the exception.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value may be null.
tr	Throwable: An exception to log. This value may be null.

Returns
int

i

Added in API level 1

public static int i (String tag, 
                String msg)

Send an INFO log message.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value cannot be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

isLoggable

Added in API level 1

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, or ASSERT. 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	String: The tag to check. This value may be null.
level	int: The level to check. Value is ASSERT, ERROR, WARN, INFO, DEBUG, or VERBOSE

Returns
boolean	Whether or not that this is allowed to be logged.

Throws
IllegalArgumentException	is thrown if the tag.length() > 23 for Nougat (7.0) and prior releases (API <= 25), there is no tag limit of concern after this API level.

println

Added in API level 1

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

Low-level logging call.

Parameters
priority	int: The priority/type of this log message Value is ASSERT, ERROR, WARN, INFO, DEBUG, or VERBOSE
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value cannot be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

v

Added in API level 1

public static int v (String tag, 
                String msg)

Send a VERBOSE log message.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value cannot be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

v

Added in API level 1

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

Send a VERBOSE log message and log the exception.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value may be null.
tr	Throwable: An exception to log. This value may be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

w

Added in API level 1

public static int w (String tag, 
                Throwable tr)

Send a WARN log message and log the exception.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
tr	Throwable: An exception to log. This value may be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

w

Added in API level 1

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

Send a WARN log message and log the exception.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value may be null.
tr	Throwable: An exception to log. This value may be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

w

Added in API level 1

public static int w (String tag, 
                String msg)

Send a WARN log message.

Parameters
tag	String: Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs. This value may be null.
msg	String: The message you would like logged. This value cannot be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

wtf

Added in API level 8

public static int wtf (String tag, 
                String msg)

What a Terrible Failure: Report a condition that should never happen. The error will always be logged at level ASSERT with the call stack. Depending on system configuration, a report may be added to the DropBoxManager and/or the process may be terminated immediately with an error dialog.

Parameters
tag	String: Used to identify the source of a log message. This value may be null.
msg	String: The message you would like logged. This value may be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

wtf

Added in API level 8

public static int wtf (String tag, 
                Throwable tr)

What a Terrible Failure: Report an exception that should never happen. Similar to wtf(java.lang.String, java.lang.String), with an exception to log.

Parameters
tag	String: Used to identify the source of a log message. This value may be null.
tr	Throwable: An exception to log. This value cannot be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).

wtf

Added in API level 8

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

What a Terrible Failure: Report an exception that should never happen. Similar to wtf(java.lang.String, java.lang.Throwable), with a message as well.

Parameters
tag	String: Used to identify the source of a log message. This value may be null.
msg	String: The message you would like logged. This value may be null.
tr	Throwable: An exception to log. May be null.

Returns
int	A positive value if the message was loggable (see isLoggable(String, int)).