Thread.UncaughtExceptionHandler
public class ThreadGroup extends Object implements Thread.UncaughtExceptionHandler
A thread group has a name and maximum priority. The name is specified when creating the group and cannot be changed. The group's maximum priority is the maximum priority for threads created in the group. It is initially inherited from the parent thread group but may be changed using the setMaxPriority
method.
A thread group is weakly reachable from its parent group so that it is eligible for garbage collection when there are no live threads in the group and the thread group is otherwise unreachable.
Unless otherwise specified, passing a null
argument to a constructor or method in this class will cause a NullPointerException
to be thrown.
Thread.getThreadGroup
method when invoked on a virtual thread. The thread group differs to other thread groups in that its maximum priority is fixed and cannot be changed with the setMaxPriority
method. Virtual threads are not included in the estimated thread count returned by the activeCount
method, are not enumerated by the enumerate
method, and are not interrupted by the interrupt
method.Constructor | Description |
---|---|
ThreadGroup |
Constructs a new thread group. |
ThreadGroup |
Creates a new thread group. |
Modifier and Type | Method | Description |
---|---|---|
int |
activeCount() |
Returns an estimate of the number of live platform threads in this thread group and its subgroups. |
int |
activeGroupCount() |
Returns an estimate of the number of groups in this thread group and its subgroups. |
final void |
checkAccess() |
Deprecated, for removal: This API element is subject to removal in a future version. This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. |
final void |
destroy() |
Deprecated, for removal: This API element is subject to removal in a future version. This method was originally specified to destroy an empty thread group. |
int |
enumerate |
Copies into the specified array every live platform thread in this thread group and its subgroups. |
int |
enumerate |
Copies into the specified array every live platform thread in this thread group. |
int |
enumerate |
Copies into the specified array references to every subgroup in this thread group and its subgroups. |
int |
enumerate |
Copies into the specified array references to every subgroup 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 live platform threads in this thread group and its subgroups. |
final boolean |
isDaemon() |
Deprecated, for removal: This API element is subject to removal in a future version. This method originally indicated if the thread group is a daemon thread group that is automatically destroyed when its last thread terminates. |
boolean |
isDestroyed() |
Deprecated, for removal: This API element is subject to removal in a future version. This method originally indicated if the thread group is destroyed. |
void |
list() |
Prints information about this thread group to the standard output. |
final boolean |
parentOf |
Tests if this thread group is either the thread group argument or one of its ancestor thread groups. |
final void |
resume() |
Deprecated, for removal: This API element is subject to removal in a future version. This method was originally specified to resume all threads in the thread group. |
final void |
setDaemon |
Deprecated, for removal: This API element is subject to removal in a future version. This method originally configured whether the thread group is a daemon thread group that is automatically destroyed when its last thread terminates. |
final void |
setMaxPriority |
Sets the maximum priority of the group. |
final void |
stop() |
Deprecated, for removal: This API element is subject to removal in a future version. This method was originally specified to stop all threads in the thread group. |
final void |
suspend() |
Deprecated, for removal: This API element is subject to removal in a future version. This method was originally specified to suspend all threads in the thread group. |
String |
toString() |
Returns a string representation of this Thread group. |
void |
uncaughtException |
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. |
public ThreadGroup(String name)
The checkAccess
method of the parent thread group is called with no arguments; this may result in a security exception.
name
- the name of the new thread group, can be null
SecurityException
- if the current thread cannot create a thread in the specified thread group.public ThreadGroup(ThreadGroup parent, String name)
The checkAccess
method of the parent thread group is called with no arguments; this may result in a security exception.
parent
- the parent thread group.name
- the name of the new thread group, can be null
SecurityException
- if the current thread cannot create a thread in the specified thread group.public final String getName()
null
public final ThreadGroup getParent()
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.
null
.SecurityException
- if the current thread cannot modify this thread group.public final int getMaxPriority()
@Deprecated(since="16", forRemoval=true) public final boolean isDaemon()
@Deprecated(since="16", forRemoval=true) public boolean isDestroyed()
@Deprecated(since="16", forRemoval=true) public final void setDaemon(boolean daemon)
First, the checkAccess
method of this thread group is called with no arguments; this may result in a security exception.
daemon
- the daemon statusSecurityException
- if the current thread cannot modify this thread group.public final void setMaxPriority(int pri)
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 Thread.MIN_PRIORITY
or greater than Thread.MAX_PRIORITY
, the maximum priority of the group remains unchanged.
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.
pri
- the new priority of the thread group.SecurityException
- if the current thread cannot modify this thread group.public final boolean parentOf(ThreadGroup g)
g
- a thread group, can be null
true
if this thread group is the thread group argument or one of its ancestor thread groups; false
otherwise.@Deprecated(since="17", forRemoval=true) public final void checkAccess()
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
.
SecurityException
- if the current thread is not allowed to access this thread group.public int activeCount()
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.
public int enumerate(Thread[] list)
An invocation of this method behaves in exactly the same way as the invocation
enumerate(list, true)
list
- an array into which to put the list of threadsSecurityException
- if checkAccess determines that the current thread cannot access this thread grouppublic int enumerate(Thread[] list, boolean recurse)
recurse
is true
, this method recursively enumerates all subgroups of this thread group and references to every live platform 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 live 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.
list
- an array into which to put the list of threadsrecurse
- if true
, recursively enumerate all subgroups of this thread groupSecurityException
- if checkAccess determines that the current thread cannot access this thread grouppublic int activeGroupCount()
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.
public int enumerate(ThreadGroup[] list)
An invocation of this method behaves in exactly the same way as the invocation
enumerate(list, true)
list
- an array into which to put the list of thread groupsSecurityException
- if checkAccess determines that the current thread cannot access this thread grouppublic int enumerate(ThreadGroup[] list, boolean recurse)
recurse
is true
, this method recursively enumerates all subgroups of this thread group and references to every 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 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.
list
- an array into which to put the list of thread groupsrecurse
- if true
, recursively enumerate all subgroupsSecurityException
- if checkAccess determines that the current thread cannot access this thread group@Deprecated(since="1.2", forRemoval=true) public final void stop()
UnsupportedOperationException
.public final void interrupt()
SecurityException
- if the current thread is not allowed to access this thread group or any of the threads in the thread group.@Deprecated(since="1.2", forRemoval=true) public final void suspend()
UnsupportedOperationException
.@Deprecated(since="1.2", forRemoval=true) public final void resume()
UnsupportedOperationException
.@Deprecated(since="16", forRemoval=true) public final void destroy()
public void list()
public void uncaughtException(Thread t, Throwable e)
Thread.UncaughtExceptionHandler
installed. The uncaughtException
method of ThreadGroup
does the following:
uncaughtException
method of that parent is called with the same two arguments. uncaughtException
method is called with the same two arguments. 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.
uncaughtException
in interface Thread.UncaughtExceptionHandler
t
- the thread that is about to exit.e
- the uncaught exception.public String toString()
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/ThreadGroup.html