public class

Thread

extends Object
implements Runnable

java.lang.Object
↳	java.lang.Thread

Known Direct Subclasses

HandlerThread

Class Overview

A Thread is a unit of concurrent execution. It has its own call stack for methods being called and their parameters. Threads in the same VM interact and synchronize by the use of shared Objects and monitors associated with these objects. Synchronized methods and part of the API in Object also allow Threads to cooperate.

Summary

Nested Classes
public class	Thread.State	A representation of a thread's state.
public class	Thread.UncaughtExceptionHandler	Implemented by objects that want to handle cases where a thread is being terminated by an uncaught exception.

Constants
int	MAX_PRIORITY	The maximum priority value allowed for a thread.
int	MIN_PRIORITY	The minimum priority value allowed for a thread.
int	NORM_PRIORITY	The normal (default) priority value assigned to threads.

Public Constructors
	Thread() Constructs a new Thread with no runnable object and a newly generated name.
	Thread(Runnable runnable) Constructs a new Thread with a runnable object and a newly generated name.
	Thread(Runnable runnable, String threadName) Constructs a new Thread with a runnable object and name provided.
	Thread(String threadName) Constructs a new Thread with no runnable object and the name provided.
	Thread(ThreadGroup group, Runnable runnable) Constructs a new Thread with a runnable object and a newly generated name.
	Thread(ThreadGroup group, Runnable runnable, String threadName) Constructs a new Thread with a runnable object, the given name and belonging to the ThreadGroup passed as parameter.
	Thread(ThreadGroup group, String threadName) Constructs a new Thread with no runnable object, the given name and belonging to the ThreadGroup passed as parameter.
	Thread(ThreadGroup group, Runnable runnable, String threadName, long stackSize) Constructs a new Thread with a runnable object, the given name and belonging to the ThreadGroup passed as parameter.

Public Methods
static int	activeCount() Returns the number of active threads in the running thread's ThreadGroup and its subgroups.
final void	checkAccess() This method is used for operations that require approval from a SecurityManager.
int	countStackFrames() This method is deprecated. The results of this call were never well defined. To make things worse, it would depend if the Thread was suspended or not, and suspend was deprecated too.
static Thread	currentThread() Returns the instance of Thread that corresponds to the running Thread which calls this method.
void	destroy() This method is deprecated. Not implemented.
static void	dumpStack() Prints a text representation of the stack for this Thread.
static int	enumerate(Thread[] threads) Copies an array with all Threads which are in the same ThreadGroup as the receiver - and subgroups - into the array `threads` passed as parameter.
static Map<Thread, StackTraceElement[]>	getAllStackTraces() Returns the stack traces of all the currently live threads and puts them into the given map.
ClassLoader	getContextClassLoader() Returns the context ClassLoader for the receiver.
static Thread.UncaughtExceptionHandler	getDefaultUncaughtExceptionHandler() Returns the default exception handler that's executed when uncaught exception terminates a thread.
long	getId() Returns the thread's identifier.
final String	getName() Returns the name of the receiver.
final int	getPriority() Returns the priority of the receiver.
StackTraceElement[]	getStackTrace() Returns the current stack trace of the thread.
Thread.State	getState() Returns the current state of the thread for monitoring purposes.
final ThreadGroup	getThreadGroup() Returns the ThreadGroup to which the receiver belongs
Thread.UncaughtExceptionHandler	getUncaughtExceptionHandler() Returns the thread's uncaught exception handler.
static boolean	holdsLock(Object object) Returns whether the current thread has a monitor lock on the specified object.
void	interrupt() Posts an interrupt request to the receiver.
static boolean	interrupted() Returns a `boolean` indicating whether the current Thread ( `currentThread()`) has a pending interrupt request ( `true`) or not (`false`).
final boolean	isAlive() Returns `true` if the receiver has already been started and still runs code (hasn't died yet).
final boolean	isDaemon() Returns a `boolean` indicating whether the receiver is a daemon Thread (`true`) or not (`false`) A daemon Thread only runs as long as there are non-daemon Threads running.
boolean	isInterrupted() Returns a `boolean` indicating whether the receiver has a pending interrupt request (`true`) or not ( `false`)
final void	join() Blocks the current Thread (`Thread.currentThread()`) until the receiver finishes its execution and dies.
final void	join(long millis, int nanos) Blocks the current Thread (`Thread.currentThread()`) until the receiver finishes its execution and dies or the specified timeout expires, whatever happens first.
final void	join(long millis) Blocks the current Thread (`Thread.currentThread()`) until the receiver finishes its execution and dies or the specified timeout expires, whatever happens first.
final void	resume() This method is deprecated. Used with deprecated method suspend()
void	run() Calls the `run()` method of the Runnable object the receiver holds.
void	setContextClassLoader(ClassLoader cl) Set the context ClassLoader for the receiver.
final void	setDaemon(boolean isDaemon) Set if the receiver is a daemon Thread or not.
static void	setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler handler) Sets the default uncaught exception handler.
final void	setName(String threadName) Sets the name of the receiver.
final void	setPriority(int priority) Sets the priority of the receiver.
void	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler handler) Sets the default uncaught exception handler.
static void	sleep(long time, int nanos) Causes the thread which sent this message to sleep an interval of time (given in milliseconds).
static void	sleep(long time) Causes the thread which sent this message to sleep an interval of time (given in milliseconds).
synchronized void	start() Starts the new Thread of execution.
final void	stop() This method is deprecated. No replacement.
synchronized final void	stop(Throwable throwable) This method is deprecated. No replacement.
final void	suspend() This method is deprecated. May cause deadlocks.
String	toString() Returns a string containing a concise, human-readable description of the receiver.
static void	yield() Causes the thread which sent this message to yield execution to another Thread that is ready to run.

[Expand]

Inherited Methods

From class java.lang.Object

Object	clone() Returns a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	equals(Object o) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
void	finalize() Called by the virtual machine when there are no longer any (non-weak) references to the receiver.
final Class<? extends Object>	getClass() Returns the unique instance of java.lang.Class which represents the class of the receiver.
int	hashCode() Returns an integer hash code for the receiver.
final void	notify() Causes one thread which is `wait` ing on the receiver to be made ready to run.
final void	notifyAll() Causes all threads which are `wait` ing on the receiver to be made ready to run.
String	toString() Returns a string containing a concise, human-readable description of the receiver.
final void	wait(long time, int frac) Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by `notify` or `notifyAll`) or the expiration of the timeout.
final void	wait(long time) Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by `notify` or `notifyAll`) or the expiration of the timeout.
final void	wait() Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by `notify` or `notifyAll`).

From interface java.lang.Runnable

Constants

public static final int MAX_PRIORITY

The maximum priority value allowed for a thread.

Constant Value: 10 (0x0000000a)

public static final int MIN_PRIORITY

The minimum priority value allowed for a thread.

Constant Value: 1 (0x00000001)

public static final int NORM_PRIORITY

The normal (default) priority value assigned to threads.

Constant Value: 5 (0x00000005)

Public Constructors

public Thread ()

Constructs a new Thread with no runnable object and a newly generated name. The new Thread will belong to the same ThreadGroup as the Thread calling this constructor.

public Thread (Runnable runnable)

Constructs a new Thread with a runnable object and a newly generated name. The new Thread will belong to the same ThreadGroup as the Thread calling this constructor.

Parameters

runnable	a java.lang.Runnable whose method `run` will be executed by the new Thread

public Thread (Runnable runnable, String threadName)

Constructs a new Thread with a runnable object and name provided. The new Thread will belong to the same ThreadGroup as the Thread calling this constructor.

Parameters

runnable	a java.lang.Runnable whose method `run` will be executed by the new Thread
threadName	Name for the Thread being created

public Thread (String threadName)

Constructs a new Thread with no runnable object and the name provided. The new Thread will belong to the same ThreadGroup as the Thread calling this constructor.

Parameters

threadName	Name for the Thread being created

public Thread (ThreadGroup group, Runnable runnable)

Constructs a new Thread with a runnable object and a newly generated name. The new Thread will belong to the ThreadGroup passed as parameter.

Parameters

group	ThreadGroup to which the new Thread will belong
runnable	a java.lang.Runnable whose method `run` will be executed by the new Thread

Throws

SecurityException	if `group.checkAccess()` fails with a SecurityException
IllegalThreadStateException	if `group.destroy()` has already been done

public Thread (ThreadGroup group, Runnable runnable, String threadName)

Constructs a new Thread with a runnable object, the given name and belonging to the ThreadGroup passed as parameter.

Parameters

group	ThreadGroup to which the new Thread will belong
runnable	a java.lang.Runnable whose method `run` will be executed by the new Thread
threadName	Name for the Thread being created

Throws

SecurityException	if `group.checkAccess()` fails with a SecurityException
IllegalThreadStateException	if `group.destroy()` has already been done

public Thread (ThreadGroup group, String threadName)

Constructs a new Thread with no runnable object, the given name and belonging to the ThreadGroup passed as parameter.

Parameters

group	ThreadGroup to which the new Thread will belong
threadName	Name for the Thread being created

Throws

SecurityException	if `group.checkAccess()` fails with a SecurityException
IllegalThreadStateException	if `group.destroy()` has already been done

public Thread (ThreadGroup group, Runnable runnable, String threadName, long stackSize)

Constructs a new Thread with a runnable object, the given name and belonging to the ThreadGroup passed as parameter.

Parameters

group	ThreadGroup to which the new Thread will belong
runnable	a java.lang.Runnable whose method `run` will be executed by the new Thread
threadName	Name for the Thread being created
stackSize	Platform dependent stack size

Throws

SecurityException	if `group.checkAccess()` fails with a SecurityException
IllegalThreadStateException	if `group.destroy()` has already been done

Public Methods

public static int activeCount ()

Returns the number of active threads in the running thread's ThreadGroup and its subgroups.

Returns

Number of Threads

public final void checkAccess ()

This method is used for operations that require approval from a SecurityManager. If there's none installed, this method is a no-op. If there's a SecurityManager installed , checkAccess(Thread) is called for that SecurityManager.

public int countStackFrames ()

This method is deprecated.The results of this call were never well defined. To make things worse, it would depend if the Thread was suspended or not, and suspend was deprecated too.

Returns the number of stack frames in this thread.

Returns

Number of stack frames

public static Thread currentThread ()

Returns the instance of Thread that corresponds to the running Thread which calls this method.

Returns

a java.lang.Thread corresponding to the code that called currentThread()

public void destroy ()

This method is deprecated.Not implemented.

Destroys the receiver without any monitor cleanup.

public static void dumpStack ()

Prints a text representation of the stack for this Thread.

public static int enumerate (Thread[] threads)

Copies an array with all Threads which are in the same ThreadGroup as the receiver - and subgroups - into the array threads passed as parameter. If the array passed as parameter is too small no exception is thrown - the extra elements are simply not copied.

Parameters

threads	array into which the Threads will be copied

Returns

How many Threads were copied over

Throws

SecurityException	if the installed SecurityManager fails checkAccess(Thread)

public static Map<Thread, StackTraceElement[]> getAllStackTraces ()

Returns the stack traces of all the currently live threads and puts them into the given map.

Returns

A Map of current Threads to StackTraceElement arrays.

Throws

SecurityException	if the current SecurityManager fails the checkPermission(java.security.Permission) call.

public ClassLoader getContextClassLoader ()

Returns the context ClassLoader for the receiver.

If the conditions

there is a security manager
the caller's class loader is not null
the caller's class loader is not the same as or an ancestor of contextClassLoader

are satisfied, a security check for RuntimePermission("getClassLoader") is performed first.

Returns

ClassLoader The context ClassLoader

Throws

SecurityException	If aforementioned security check fails.

public static Thread.UncaughtExceptionHandler getDefaultUncaughtExceptionHandler ()

Returns the default exception handler that's executed when uncaught exception terminates a thread.

Returns

An Thread.UncaughtExceptionHandler or null if none exists.

public long getId ()

Returns the thread's identifier. The ID is a positive long generated on thread creation, is unique to the thread and doesn't change during the life of the thread; the ID may be reused after the thread has been terminated.

Returns

The thread's ID.

public final String getName ()

Returns the name of the receiver.

Returns

the receiver's name (a java.lang.String)

public final int getPriority ()

Returns the priority of the receiver.

Returns

the receiver's priority (an int)

public StackTraceElement[] getStackTrace ()

Returns the current stack trace of the thread.

The RuntimePermission("getStackTrace") is checked before returning a result.

Returns

An array of StackTraceElements.

Throws

SecurityException	if the current SecurityManager fails the checkPermission(java.security.Permission) call.

public Thread.State getState ()

Returns the current state of the thread for monitoring purposes.

Returns

A State value.

public final ThreadGroup getThreadGroup ()

Returns the ThreadGroup to which the receiver belongs

Returns

the receiver's ThreadGroup

public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler ()

Returns the thread's uncaught exception handler. If not explicitly set, then the ThreadGroup's handler is returned. If the thread is terminated, then null is returned.

Returns

An UncaughtExceptionHandler instance or null.

public static boolean holdsLock (Object object)

Returns whether the current thread has a monitor lock on the specified object.

Parameters

object	the object to test for the monitor lock

Returns

true when the current thread has a monitor lock on the specified object

public void interrupt ()

Posts an interrupt request to the receiver.

Throws

SecurityException	if `checkAccess()` fails with a SecurityException

public static boolean interrupted ()

Returns a boolean indicating whether the current Thread ( currentThread()) has a pending interrupt request ( true) or not (false). It also has the side-effect of clearing the flag.

Returns

a boolean

public final boolean isAlive ()

Returns true if the receiver has already been started and still runs code (hasn't died yet). Returns false either if the receiver hasn't been started yet or if it has already started and run to completion and died.

Returns

a boolean

public final boolean isDaemon ()

Returns a boolean indicating whether the receiver is a daemon Thread (true) or not (false) A daemon Thread only runs as long as there are non-daemon Threads running. When the last non-daemon Thread ends, the whole program ends no matter if it had daemon Threads still running or not.

Returns

a boolean

public boolean isInterrupted ()

Returns a boolean indicating whether the receiver has a pending interrupt request (true) or not ( false)

Returns

a boolean

public final void join ()

Blocks the current Thread (Thread.currentThread()) until the receiver finishes its execution and dies.

Throws

InterruptedException	if `interrupt()` was called for the receiver while it was in the `join()` call

public final void join (long millis, int nanos)

Blocks the current Thread (Thread.currentThread()) until the receiver finishes its execution and dies or the specified timeout expires, whatever happens first.

Parameters

millis	The maximum time to wait (in milliseconds).
nanos	Extra nanosecond precision

Throws

InterruptedException	if `interrupt()` was called for the receiver while it was in the `join()` call

public final void join (long millis)

Blocks the current Thread (Thread.currentThread()) until the receiver finishes its execution and dies or the specified timeout expires, whatever happens first.

Parameters

millis	The maximum time to wait (in milliseconds).

Throws

InterruptedException	if `interrupt()` was called for the receiver while it was in the `join()` call

public final void resume ()

This method is deprecated.Used with deprecated method suspend()

This is a no-op if the receiver was never suspended, or suspended and already resumed. If the receiver is suspended, however, makes it resume to the point where it was when it was suspended.

Throws

SecurityException	if `checkAccess()` fails with a SecurityException

public void run ()

Calls the run() method of the Runnable object the receiver holds. If no Runnable is set, does nothing.

public void setContextClassLoader (ClassLoader cl)

Set the context ClassLoader for the receiver.

The RuntimePermission("setContextClassLoader") is checked prior to setting the handler.

Parameters

cl	The context ClassLoader

Throws

SecurityException	if the current SecurityManager fails the checkPermission call.

public final void setDaemon (boolean isDaemon)

Set if the receiver is a daemon Thread or not. This can only be done before the Thread starts running.

Parameters

isDaemon	A boolean indicating if the Thread should be daemon or not

Throws

SecurityException	if `checkAccess()` fails with a SecurityException

public static void setDefaultUncaughtExceptionHandler (Thread.UncaughtExceptionHandler handler)

Sets the default uncaught exception handler.

The RuntimePermission("setDefaultUncaughtExceptionHandler") is checked prior to setting the handler.

Parameters

handler	The handler to set or `null`.

Throws

SecurityException	if the current SecurityManager fails the checkPermission call.

public final void setName (String threadName)

Sets the name of the receiver.

Parameters

threadName	new name for the Thread

Throws

SecurityException	if `checkAccess()` fails with a SecurityException

public final void setPriority (int priority)

Sets the priority of the receiver. Note that the final priority set may not be the parameter that was passed - it will depend on the receiver's ThreadGroup. The priority cannot be set to be higher than the receiver's ThreadGroup's maxPriority().

Parameters

priority	new priority for the Thread

Throws

SecurityException	if `checkAccess()` fails with a SecurityException
IllegalArgumentException	if the new priority is greater than Thread.MAX_PRIORITY or less than Thread.MIN_PRIORITY

public void setUncaughtExceptionHandler (Thread.UncaughtExceptionHandler handler)

Sets the default uncaught exception handler.

Parameters

handler	The handler to set or `null`.

Throws

SecurityException	if the current SecurityManager fails the checkAccess call.

public static void sleep (long time, int nanos)

Causes the thread which sent this message to sleep an interval of time (given in milliseconds). The precision is not guaranteed - the Thread may sleep more or less than requested.

Parameters

time	The time to sleep in milliseconds.
nanos	Extra nanosecond precision

Throws

InterruptedException	if `interrupt()` was called for this Thread while it was sleeping

public static void sleep (long time)

Causes the thread which sent this message to sleep an interval of time (given in milliseconds). The precision is not guaranteed - the Thread may sleep more or less than requested.

Parameters

time	The time to sleep in milliseconds.

Throws

InterruptedException	if `interrupt()` was called for this Thread while it was sleeping

public synchronized void start ()

Starts the new Thread of execution. The run() method of the receiver will be called by the receiver Thread itself (and not the Thread calling start()).

Throws

IllegalThreadStateException	Unspecified in the Java language specification

public final void stop ()

This method is deprecated.No replacement.

Requests the receiver Thread to stop and throw ThreadDeath. The Thread is resumed if it was suspended and awakened if it was sleeping, so that it can proceed to throw ThreadDeath.

Throws

SecurityException	if `checkAccess()` fails with a SecurityException

public final synchronized void stop (Throwable throwable)

This method is deprecated.No replacement.

Requests the receiver Thread to stop and throw the throwable(). The Thread is resumed if it was suspended and awakened if it was sleeping, so that it can proceed to throw the throwable().

Parameters

throwable	Throwable object to be thrown by the Thread

Throws

SecurityException	if `checkAccess()` fails with a SecurityException
NullPointerException	if `throwable()` is `null`

public final void suspend ()

This method is deprecated.May cause deadlocks.

This is a no-op if the receiver is suspended. If the receiver isAlive() however, suspended it until resume() is sent to it. Suspend requests are not queued, which means that N requests are equivalent to just one - only one resume request is needed in this case.

Throws

SecurityException	if `checkAccess()` fails with a SecurityException

public String toString ()

Returns a string containing a concise, human-readable description of the receiver.

Returns

a printable representation for the receiver.

public static void yield ()

Causes the thread which sent this message to yield execution to another Thread that is ready to run. The actual scheduling is implementation-dependent.

Feb	MAR	Apr
	06
2008	2009	2010

Interfaces

Classes

Enums

Exceptions

Errors

Thread

Class Overview

See Also

Summary

Constants

public static final int MAX_PRIORITY

public static final int MIN_PRIORITY

public static final int NORM_PRIORITY

Public Constructors

public Thread ()

See Also

public Thread (Runnable runnable)

Parameters

See Also

public Thread (Runnable runnable, String threadName)

Parameters

See Also

public Thread (String threadName)

Parameters

See Also

public Thread (ThreadGroup group, Runnable runnable)

Parameters

Throws

See Also

public Thread (ThreadGroup group, Runnable runnable, String threadName)

Parameters

Throws

See Also

public Thread (ThreadGroup group, String threadName)

Parameters

Throws

See Also

public Thread (ThreadGroup group, Runnable runnable, String threadName, long stackSize)

Parameters

Throws

See Also

Public Methods

public static int activeCount ()

Returns

public final void checkAccess ()

See Also

public int countStackFrames ()

Returns

public static Thread currentThread ()

Returns

public void destroy ()

public static void dumpStack ()

public static int enumerate (Thread[] threads)

Parameters

Returns

Throws

See Also

public static Map<Thread, StackTraceElement[]> getAllStackTraces ()

Returns

Throws

public ClassLoader getContextClassLoader ()

Returns

Throws

See Also

public static Thread.UncaughtExceptionHandler getDefaultUncaughtExceptionHandler ()

Returns

public long getId ()

Returns

public final String getName ()

Returns

public final int getPriority ()

Returns

See Also

public StackTraceElement[] getStackTrace ()

Returns

Throws

public Thread.State getState ()

Returns

public final ThreadGroup getThreadGroup ()

Returns