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Added in API level 1

Summary: Ctors | Methods | Inherited Methods | [Expand All]

ThreadGroup

public class ThreadGroup
extends Object implements Thread.UncaughtExceptionHandler

java.lang.Object
↳	java.lang.ThreadGroup

A thread group represents a set of threads. In addition, a thread group can also include other thread groups. The thread groups form a tree in which every thread group except the initial thread group has a parent.

A thread is allowed to access information about its own thread group, but not to access information about its thread group's parent thread group or any other thread groups.

Summary

Public constructors
`ThreadGroup(String name)` Constructs a new thread group.
`ThreadGroup(ThreadGroup parent, String name)` Creates a new thread group.

Public methods
`int`	`activeCount()` Returns an estimate of the number of active threads in this thread group and its subgroups.
`int`	`activeGroupCount()` Returns an estimate of the number of active groups in this thread group and its subgroups.
`boolean`	`allowThreadSuspension(boolean b)` This method was deprecated in API level 1. The definition of this call depends on `suspend()`, which is deprecated. Further, the behavior of this call was never specified.
`final void`	`checkAccess()` Determines if the currently running thread has permission to modify this thread group.
`final void`	`destroy()` Destroys this thread group and all of its subgroups.
`int`	`enumerate(ThreadGroup[] list)` Copies into the specified array references to every active subgroup in this thread group and its subgroups.
`int`	`enumerate(ThreadGroup[] list, boolean recurse)` Copies into the specified array references to every active subgroup in this thread group.
`int`	`enumerate(Thread[] list)` Copies into the specified array every active thread in this thread group and its subgroups.
`int`	`enumerate(Thread[] list, boolean recurse)` Copies into the specified array every active thread in this thread group.
`final int`	`getMaxPriority()` Returns the maximum priority of this thread group.
`final String`	`getName()` Returns the name of this thread group.
`final ThreadGroup`	`getParent()` Returns the parent of this thread group.
`final void`	`interrupt()` Interrupts all threads in this thread group.
`final boolean`	`isDaemon()` Tests if this thread group is a daemon thread group.
`boolean`	`isDestroyed()` Tests if this thread group has been destroyed.
`void`	`list()` Prints information about this thread group to the standard output.
`final boolean`	`parentOf(ThreadGroup g)` Tests if this thread group is either the thread group argument or one of its ancestor thread groups.
`final void`	`resume()` This method was deprecated in API level 1. This method is used solely in conjunction with `Thread.suspend` and `ThreadGroup.suspend`, both of which have been deprecated, as they are inherently deadlock-prone. See `suspend()` for details.
`final void`	`setDaemon(boolean daemon)` Changes the daemon status of this thread group.
`final void`	`setMaxPriority(int pri)` Sets the maximum priority of the group.
`final void`	`stop()` This method was deprecated in API level 1. This method is inherently unsafe. See `stop()` for details.
`final void`	`suspend()` This method was deprecated in API level 1. This method is inherently deadlock-prone. See `suspend()` for details.
`String`	`toString()` Returns a string representation of this Thread group.
`void`	`uncaughtException(Thread t, Throwable e)` Called by the Java Virtual Machine when a thread in this thread group stops because of an uncaught exception, and the thread does not have a specific `Thread.UncaughtExceptionHandler` installed.

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 millis, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void`	`wait(long millis)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void`	`wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

From interface


  
    java.lang.Thread.UncaughtExceptionHandler

Public constructors

ThreadGroup

Added in API level 1

ThreadGroup (String name)

Constructs a new thread group. The parent of this new group is the thread group of the currently running thread.

The checkAccess method of the parent thread group is called with no arguments; this may result in a security exception.

Parameters
`name`	`String`: the name of the new thread group.

Throws
`SecurityException`	if the current thread cannot create a thread in the specified thread group.

See also:

checkAccess()

ThreadGroup

Added in API level 1

ThreadGroup (ThreadGroup parent, 
                String name)

Creates a new thread group. The parent of this new group is the specified thread group.

The checkAccess method of the parent thread group is called with no arguments; this may result in a security exception.

Parameters
`parent`	`ThreadGroup`: the parent thread group.
`name`	`String`: the name of the new thread group.

Throws
`NullPointerException`	if the thread group argument is `null`.
`SecurityException`	if the current thread cannot create a thread in the specified thread group.

See also:

Public methods

activeCount

Added in API level 1

int activeCount ()

Returns an estimate of the number of active threads in this thread group and its subgroups. Recursively iterates over all subgroups in this thread group.

The value returned is only an estimate because the number of threads may change dynamically while this method traverses internal data structures, and might be affected by the presence of certain system threads. This method is intended primarily for debugging and monitoring purposes.

Returns
`int`	an estimate of the number of active threads in this thread group and in any other thread group that has this thread group as an ancestor

activeGroupCount

Added in API level 1

int activeGroupCount ()

Returns an estimate of the number of active groups in this thread group and its subgroups. Recursively iterates over all subgroups in this thread group.

The value returned is only an estimate because the number of thread groups may change dynamically while this method traverses internal data structures. This method is intended primarily for debugging and monitoring purposes.

Returns
`int`	the number of active thread groups with this thread group as an ancestor

allowThreadSuspension

Added in API level 1

boolean allowThreadSuspension (boolean b)

This method was deprecated in API level 1.
The definition of this call depends on suspend(), which is deprecated. Further, the behavior of this call was never specified.

Used by VM to control lowmem implicit suspension.

Parameters
`b`	`boolean`: boolean to allow or disallow suspension

Returns
`boolean`	true on success

checkAccess

Added in API level 1

void checkAccess ()

Determines if the currently running thread has permission to modify this thread group.

If there is a security manager, its checkAccess method is called with this thread group as its argument. This may result in throwing a SecurityException.

Throws
`SecurityException`	if the current thread is not allowed to access this thread group.

See also:

checkAccess(java.lang.ThreadGroup)

destroy

Added in API level 1

void destroy ()

Destroys this thread group and all of its subgroups. This thread group must be empty, indicating that all threads that had been in this thread group have since stopped.

First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

Throws
`IllegalThreadStateException`	if the thread group is not empty or if the thread group has already been destroyed.
`SecurityException`	if the current thread cannot modify this thread group.

See also:

checkAccess()

enumerate

Added in API level 1

int enumerate (ThreadGroup[] list)

Copies into the specified array references to every active subgroup in this thread group and its subgroups.

An invocation of this method behaves in exactly the same way as the invocation

enumerate(list, true)

Parameters
`list`	`ThreadGroup`: an array into which to put the list of thread groups

Returns
`int`	the number of thread groups put into the array

Throws
`SecurityException`	if checkAccess determines that the current thread cannot access this thread group

enumerate

Added in API level 1

int enumerate (ThreadGroup[] list, 
                boolean recurse)

Copies into the specified array references to every active subgroup in this thread group. If recurse is true, this method recursively enumerates all subgroups of this thread group and references to every active thread group in these subgroups are also included.

An application might use the activeGroupCount method to get an estimate of how big the array should be, however if the array is too short to hold all the thread groups, the extra thread groups are silently ignored. If it is critical to obtain every active subgroup in this thread group, the caller should verify that the returned int value is strictly less than the length of list.

Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.

Parameters
`list`	`ThreadGroup`: an array into which to put the list of thread groups
`recurse`	`boolean`: if `true`, recursively enumerate all subgroups

Returns
`int`	the number of thread groups put into the array

Throws
`SecurityException`	if checkAccess determines that the current thread cannot access this thread group

enumerate

Added in API level 1

int enumerate (Thread[] list)

Copies into the specified array every active thread in this thread group and its subgroups.

An invocation of this method behaves in exactly the same way as the invocation

enumerate(list, true)

Parameters
`list`	`Thread`: an array into which to put the list of threads

Returns
`int`	the number of threads put into the array

Throws
`SecurityException`	if checkAccess determines that the current thread cannot access this thread group

enumerate

Added in API level 1

int enumerate (Thread[] list, 
                boolean recurse)

Copies into the specified array every active thread in this thread group. If recurse is true, this method recursively enumerates all subgroups of this thread group and references to every active thread in these subgroups are also included. If the array is too short to hold all the threads, the extra threads are silently ignored.

An application might use the activeCount method to get an estimate of how big the array should be, however if the array is too short to hold all the threads, the extra threads are silently ignored. If it is critical to obtain every active thread in this thread group, the caller should verify that the returned int value is strictly less than the length of list.

Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.

Parameters
`list`	`Thread`: an array into which to put the list of threads
`recurse`	`boolean`: if `true`, recursively enumerate all subgroups of this thread group

Returns
`int`	the number of threads put into the array

Throws
`SecurityException`	if checkAccess determines that the current thread cannot access this thread group

getMaxPriority

Added in API level 1

int getMaxPriority ()

Returns the maximum priority of this thread group. Threads that are part of this group cannot have a higher priority than the maximum priority.

Returns
`int`	the maximum priority that a thread in this thread group can have.

See also:

setMaxPriority(int)

getName

Added in API level 1

String getName ()

Returns the name of this thread group.

Returns
`String`	the name of this thread group.

getParent

Added in API level 1

ThreadGroup getParent ()

Returns the parent of this thread group.

First, if the parent is not null, the checkAccess method of the parent thread group is called with no arguments; this may result in a security exception.

Returns
`ThreadGroup`	the parent of this thread group. The top-level thread group is the only thread group whose parent is `null`.

Throws
`SecurityException`	if the current thread cannot modify this thread group.

See also:

interrupt

Added in API level 1

void interrupt ()

Interrupts all threads in this thread group.

First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

This method then calls the interrupt method on all the threads in this thread group and in all of its subgroups.

Throws
`SecurityException`	if the current thread is not allowed to access this thread group or any of the threads in the thread group.

See also:

isDaemon

Added in API level 1

boolean isDaemon ()

Tests if this thread group is a daemon thread group. A daemon thread group is automatically destroyed when its last thread is stopped or its last thread group is destroyed.

Returns
`boolean`	`true` if this thread group is a daemon thread group; `false` otherwise.

isDestroyed

Added in API level 1

boolean isDestroyed ()

Tests if this thread group has been destroyed.

Returns
`boolean`	true if this object is destroyed

list

Added in API level 1

void list ()

Prints information about this thread group to the standard output. This method is useful only for debugging.

parentOf

Added in API level 1

boolean parentOf (ThreadGroup g)

Tests if this thread group is either the thread group argument or one of its ancestor thread groups.

Parameters
`g`	`ThreadGroup`: a thread group.

Returns
`boolean`	`true` if this thread group is the thread group argument or one of its ancestor thread groups; `false` otherwise.

resume

Added in API level 1

void resume ()

This method was deprecated in API level 1.
This method is used solely in conjunction with Thread.suspend and ThreadGroup.suspend, both of which have been deprecated, as they are inherently deadlock-prone. See suspend() for details.

Resumes all threads in this thread group.

First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

This method then calls the resume method on all the threads in this thread group and in all of its sub groups.

Throws
`SecurityException`	if the current thread is not allowed to access this thread group or any of the threads in the thread group.

See also:

setDaemon

Added in API level 1

void setDaemon (boolean daemon)

Changes the daemon status of this thread group.

First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

A daemon thread group is automatically destroyed when its last thread is stopped or its last thread group is destroyed.

Parameters
`daemon`	`boolean`: if `true`, marks this thread group as a daemon thread group; otherwise, marks this thread group as normal.

Throws
`SecurityException`	if the current thread cannot modify this thread group.

See also:

setMaxPriority

Added in API level 1

void setMaxPriority (int pri)

Sets the maximum priority of the group. Threads in the thread group that already have a higher priority are not affected.

First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

If the pri argument is less than MIN_PRIORITY or greater than MAX_PRIORITY, it is clamped to those values.

Otherwise, the priority of this ThreadGroup object is set to the smaller of the specified pri and the maximum permitted priority of the parent of this thread group. (If this thread group is the system thread group, which has no parent, then its maximum priority is simply set to pri.) Then this method is called recursively, with pri as its argument, for every thread group that belongs to this thread group.

Parameters
`pri`	`int`: the new priority of the thread group.

Throws
`SecurityException`	if the current thread cannot modify this thread group.

See also:

stop

Added in API level 1

void stop ()

This method was deprecated in API level 1.
This method is inherently unsafe. See stop() for details.

Stops all threads in this thread group.

First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

This method then calls the stop method on all the threads in this thread group and in all of its subgroups.

Throws
`SecurityException`	if the current thread is not allowed to access this thread group or any of the threads in the thread group.

See also:

suspend

Added in API level 1

void suspend ()

This method was deprecated in API level 1.
This method is inherently deadlock-prone. See suspend() for details.

Suspends all threads in this thread group.

First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

This method then calls the suspend method on all the threads in this thread group and in all of its subgroups.

Throws
`SecurityException`	if the current thread is not allowed to access this thread group or any of the threads in the thread group.

See also:

toString

Added in API level 1

String toString ()

Returns a string representation of this Thread group.

Returns
`String`	a string representation of this thread group.

uncaughtException

Added in API level 1

void uncaughtException (Thread t, 
                Throwable e)

Called by the Java Virtual Machine when a thread in this thread group stops because of an uncaught exception, and the thread does not have a specific Thread.UncaughtExceptionHandler installed.

The uncaughtException method of ThreadGroup does the following:

If this thread group has a parent thread group, the uncaughtException method of that parent is called with the same two arguments.
Otherwise, this method checks to see if there is a default uncaught exception handler installed, and if so, its uncaughtException method is called with the same two arguments.
Otherwise, this method determines if the Throwable argument is an instance of ThreadDeath. If so, nothing special is done. Otherwise, a message containing the thread's name, as returned from the thread's getName method, and a stack backtrace, using the Throwable's printStackTrace method, is printed to the standard error stream.

Applications can override this method in subclasses of ThreadGroup to provide alternative handling of uncaught exceptions.

Parameters
`t`	`Thread`: the thread that is about to exit.
`e`	`Throwable`: the uncaught exception.