2,threadgroup Concepts and usage

When a task requires more than one child thread to handle the business, it is not desirable that these sub-threads be disorganized, and the thread groups are created when they need to be managed uniformly.

Threadgroup API description, where red is the common method

Method Summary
int	activeCount() Returns the estimated number of active threads in this thread group.
int	activeGroupCount() Returns the estimated number of active thread groups in this thread group.
boolean	allowThreadSuspension(boolean b) is obsolete. The definition of this call depends on suspend (), which is deprecated. Further, the behavior of this call is never specified.
void	checkAccess() Determines whether the currently running thread has permission to modify this thread group.
void	destroy() Destroys this thread group and all its child groups.
int	enumerate(Thread[] list) Copies all active threads in this thread group and its subgroups into the specified array.
int	enumerate(Thread[] list, boolean recurse) Copies all the active threads in this thread group into the specified array.
int	enumerate(ThreadGroup[] list) Copies a reference to all active subgroups in this thread group into the specified array.
int	enumerate(ThreadGroup[] list, boolean recurse) Copies a reference to all active subgroups in this thread group into the specified array.
int	getMaxPriority() Returns the highest priority for this thread group.
String	getName() Returns the name of this thread group.
ThreadGroup	getParent() Returns the parent thread group for this thread group.
void	interrupt() Interrupts all threads in this thread group.
boolean	isDaemon() Tests whether this thread group is a background program thread group.
boolean	isDestroyed() Tests whether this thread group has been destroyed.
void	list() Prints information about this thread group to standard output.
boolean	parentOf(ThreadGroup g) Tests whether this thread group is a thread group parameter or one of its ancestor thread groups.
void	resume() is obsolete. This method is only used for federated Thread.Suspend and threadgroup.suspend , because they are inherently prone to deadlocks, so both are deprecated. For more information, see Thread.Suspend ().
void	setDaemon(boolean daemon) Change the background program state for this thread group.
void	setMaxPriority(int pri) Sets the highest priority for the thread group.
void	stop() is obsolete. This method has inherent insecurity. For more information, see Thread.stop ().
void	suspend() is obsolete. This method easily leads to deadlocks. For more information, see Thread.Suspend ().
String	toString() Returns a string representation of this thread group.
void	uncaughtException(Thread t, Throwable e) This method is called by 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.

2,threadgroup Concepts and usage