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ThreadGroup.javaAPI DocJava SE 6 API34555Tue Jun 10 00:25:38 BST 2008java.lang

ThreadGroup

public class ThreadGroup extends Object implements Thread$UncaughtExceptionHandler
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.

author
unascribed
version
1.65, 11/17/05
since
JDK1.0

Fields Summary
ThreadGroup
parent
String
name
int
maxPriority
boolean
destroyed
boolean
daemon
boolean
vmAllowSuspension
int
nUnstartedThreads
int
nthreads
Thread[]
threads
int
ngroups
ThreadGroup[]
groups
Constructors Summary
private ThreadGroup()
Creates an empty Thread group that is not in any Thread group. This method is used to create the system Thread group.


                                
      	// called from C code
	this.name = "system";
	this.maxPriority = Thread.MAX_PRIORITY;
    
public 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.

param
name the name of the new thread group.
exception
SecurityException if the current thread cannot create a thread in the specified thread group.
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

	this(Thread.currentThread().getThreadGroup(), name);
    
public 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.

param
parent the parent thread group.
param
name the name of the new thread group.
exception
NullPointerException if the thread group argument is null.
exception
SecurityException if the current thread cannot create a thread in the specified thread group.
see
java.lang.SecurityException
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

	if (parent == null) {
	    throw new NullPointerException();
	}
	parent.checkAccess();
	this.name = name;
	this.maxPriority = parent.maxPriority;
	this.daemon = parent.daemon;
	this.vmAllowSuspension = parent.vmAllowSuspension;
	this.parent = parent;
	parent.add(this);
    
Methods Summary
public intactiveCount()
Returns an estimate of the number of active threads in this thread group. The result might not reflect concurrent activity, and might be affected by the presence of certain system threads.

Due to the inherently imprecise nature of the result, it is recommended that this method only be used for informational purposes.

return
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.
since
JDK1.0

	int result;
	// Snapshot sub-group data so we don't hold this lock
	// while our children are computing.
	int ngroupsSnapshot;
	ThreadGroup[] groupsSnapshot;
	synchronized (this) {
	    if (destroyed) {
		return 0;
	    }
	    result = nthreads;
	    ngroupsSnapshot = ngroups;
	    if (groups != null) {
		groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
	    } else {
		groupsSnapshot = null;
	    }
	}
	for (int i = 0 ; i < ngroupsSnapshot ; i++) {
	    result += groupsSnapshot[i].activeCount();
	}
	return result;
    
public intactiveGroupCount()
Returns an estimate of the number of active groups in this thread group. The result might not reflect concurrent activity.

Due to the inherently imprecise nature of the result, it is recommended that this method only be used for informational purposes.

return
the number of active thread groups with this thread group as an ancestor.
since
JDK1.0

	int ngroupsSnapshot;
	ThreadGroup[] groupsSnapshot;
	synchronized (this) {
	    if (destroyed) {
		return 0;
	    }
	    ngroupsSnapshot = ngroups;
	    if (groups != null) {
		groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
	    } else {
		groupsSnapshot = null;
	    }
	}
	int n = ngroupsSnapshot;
	for (int i = 0 ; i < ngroupsSnapshot ; i++) {
	    n += groupsSnapshot[i].activeGroupCount();
	}
	return n;
    
private final voidadd(java.lang.ThreadGroup g)
Adds the specified Thread group to this group.

param
g the specified Thread group to be added
exception
IllegalThreadStateException If the Thread group has been destroyed.

	synchronized (this) {
	    if (destroyed) {
		throw new IllegalThreadStateException();
	    }
	    if (groups == null) {
		groups = new ThreadGroup[4];
	    } else if (ngroups == groups.length) {
		groups = Arrays.copyOf(groups, ngroups * 2);
	    }
	    groups[ngroups] = g;

	    // This is done last so it doesn't matter in case the
	    // thread is killed
	    ngroups++;
	}
    
voidadd(java.lang.Thread t)
Adds the specified Thread to this group.

param
t the Thread to be added
exception
IllegalThreadStateException If the Thread group has been destroyed.

	synchronized (this) {
	    if (destroyed) {
		throw new IllegalThreadStateException();
	    }
	    if (threads == null) {
		threads = new Thread[4];
	    } else if (nthreads == threads.length) {
                threads = Arrays.copyOf(threads, nthreads * 2);
	    }
	    threads[nthreads] = t;

	    // This is done last so it doesn't matter in case the
	    // thread is killed
	    nthreads++;
            nUnstartedThreads--;
	}
    
voidaddUnstarted()
Increments the count of unstarted threads in the thread group. Unstarted threads are not added to the thread group so that they can be collected if they are never started, but they must be counted so that daemon thread groups with unstarted threads in them are not destroyed.

        synchronized(this) {
            if (destroyed) {
                throw new IllegalThreadStateException();
            }
            nUnstartedThreads++;
        }
    
public booleanallowThreadSuspension(boolean b)
Used by VM to control lowmem implicit suspension.

param
b boolean to allow or disallow suspension
return
true on success
since
JDK1.1
deprecated
The definition of this call depends on {@link #suspend}, which is deprecated. Further, the behavior of this call was never specified.

	this.vmAllowSuspension = b;
	if (!b) {
	    VM.unsuspendSomeThreads();
	}
	return true;
    
public final voidcheckAccess()
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.

exception
SecurityException if the current thread is not allowed to access this thread group.
see
java.lang.SecurityManager#checkAccess(java.lang.ThreadGroup)
since
JDK1.0

	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkAccess(this);
	}
    
public final voiddestroy()
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.

exception
IllegalThreadStateException if the thread group is not empty or if the thread group has already been destroyed.
exception
SecurityException if the current thread cannot modify this thread group.
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

	int ngroupsSnapshot;
	ThreadGroup[] groupsSnapshot;
	synchronized (this) {
	    checkAccess();
	    if (destroyed || (nthreads > 0)) {
		throw new IllegalThreadStateException();
	    }
	    ngroupsSnapshot = ngroups;
	    if (groups != null) {
		groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
	    } else {
		groupsSnapshot = null;
	    }
	    if (parent != null) {
		destroyed = true;
		ngroups = 0;
		groups = null;
		nthreads = 0;
		threads = null;
	    }
	}
	for (int i = 0 ; i < ngroupsSnapshot ; i += 1) {
	    groupsSnapshot[i].destroy();
	}
	if (parent != null) {
	    parent.remove(this);
	}
    
public intenumerate(java.lang.Thread[] list)
Copies into the specified array every active thread in this thread group and its subgroups.

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

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 and its subgroups, 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 informational purposes.

param
list an array into which to place the list of threads.
return
the number of threads put into the array.
exception
SecurityException if the current thread does not have permission to enumerate this thread group.
see
java.lang.ThreadGroup#activeCount()
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

        checkAccess();
	return enumerate(list, 0, true);
    
public intenumerate(java.lang.Thread[] list, boolean recurse)
Copies into the specified array every active thread in this thread group. If the recurse flag is true, references to every active thread in this thread's subgroups are also included. If the array is too short to hold all the threads, the extra threads are silently ignored.

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

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 informational purposes.

param
list an array into which to place the list of threads.
param
recurse a flag indicating whether also to include threads in thread groups that are subgroups of this thread group.
return
the number of threads placed into the array.
exception
SecurityException if the current thread does not have permission to enumerate this thread group.
see
java.lang.ThreadGroup#activeCount()
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

        checkAccess();
	return enumerate(list, 0, recurse);
    
private intenumerate(java.lang.Thread[] list, int n, boolean recurse)

	int ngroupsSnapshot = 0;
	ThreadGroup[] groupsSnapshot = null;
	synchronized (this) {
	    if (destroyed) {
		return 0;
	    }
	    int nt = nthreads;
	    if (nt > list.length - n) {
		nt = list.length - n;
	    }
	    for (int i = 0; i < nt; i++) {
                if (threads[i].isAlive()) {
                    list[n++] = threads[i];
                }
            }
	    if (recurse) {
		ngroupsSnapshot = ngroups;
		if (groups != null) {
                    groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
		} else {
		    groupsSnapshot = null;
		}
	    }
	}
	if (recurse) {
	    for (int i = 0 ; i < ngroupsSnapshot ; i++) {
		n = groupsSnapshot[i].enumerate(list, n, true);
	    }
	}
	return n;
    
public intenumerate(java.lang.ThreadGroup[] list)
Copies into the specified array references to every active subgroup in this thread group.

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

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 informational purposes.

param
list an array into which to place the list of thread groups.
return
the number of thread groups put into the array.
exception
SecurityException if the current thread does not have permission to enumerate this thread group.
see
java.lang.ThreadGroup#activeGroupCount()
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

        checkAccess();
	return enumerate(list, 0, true);
    
public intenumerate(java.lang.ThreadGroup[] list, boolean recurse)
Copies into the specified array references to every active subgroup in this thread group. If the recurse flag is true, references to all active subgroups of the subgroups and so forth are also included.

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

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 informational purposes.

param
list an array into which to place the list of threads.
param
recurse a flag indicating whether to recursively enumerate all included thread groups.
return
the number of thread groups put into the array.
exception
SecurityException if the current thread does not have permission to enumerate this thread group.
see
java.lang.ThreadGroup#activeGroupCount()
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

        checkAccess();
	return enumerate(list, 0, recurse);
    
private intenumerate(java.lang.ThreadGroup[] list, int n, boolean recurse)

	int ngroupsSnapshot = 0;
	ThreadGroup[] groupsSnapshot = null;
	synchronized (this) {
	    if (destroyed) {
		return 0;
	    }
	    int ng = ngroups;
	    if (ng > list.length - n) {
		ng = list.length - n;
	    }
	    if (ng > 0) {
		System.arraycopy(groups, 0, list, n, ng);
		n += ng;
	    }
	    if (recurse) {
		ngroupsSnapshot = ngroups;
		if (groups != null) {
                    groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
		} else {
		    groupsSnapshot = null;
		}
	    }
	}
	if (recurse) {
	    for (int i = 0 ; i < ngroupsSnapshot ; i++) {
		n = groupsSnapshot[i].enumerate(list, n, true);
	    }
	}
	return n;
    
public final intgetMaxPriority()
Returns the maximum priority of this thread group. Threads that are part of this group cannot have a higher priority than the maximum priority.

return
the maximum priority that a thread in this thread group can have.
see
#setMaxPriority
since
JDK1.0

	return maxPriority;
    
public final java.lang.StringgetName()
Returns the name of this thread group.

return
the name of this thread group.
since
JDK1.0

	return name;
    
public final java.lang.ThreadGroupgetParent()
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.

return
the parent of this thread group. The top-level thread group is the only thread group whose parent is null.
exception
SecurityException if the current thread cannot modify this thread group.
see
java.lang.ThreadGroup#checkAccess()
see
java.lang.SecurityException
see
java.lang.RuntimePermission
since
JDK1.0

	if (parent != null)
	    parent.checkAccess();
	return parent;
    
public final voidinterrupt()
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.

exception
SecurityException if the current thread is not allowed to access this thread group or any of the threads in the thread group.
see
java.lang.Thread#interrupt()
see
java.lang.SecurityException
see
java.lang.ThreadGroup#checkAccess()
since
1.2

	int ngroupsSnapshot;
	ThreadGroup[] groupsSnapshot;
	synchronized (this) {
	    checkAccess();
	    for (int i = 0 ; i < nthreads ; i++) {
		threads[i].interrupt();
	    }
	    ngroupsSnapshot = ngroups;
	    if (groups != null) {
		groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
	    } else {
		groupsSnapshot = null;
	    }
	}
	for (int i = 0 ; i < ngroupsSnapshot ; i++) {
	    groupsSnapshot[i].interrupt();
	}
    
public final booleanisDaemon()
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.

return
true if this thread group is a daemon thread group; false otherwise.
since
JDK1.0

	return daemon;
    
public synchronized booleanisDestroyed()
Tests if this thread group has been destroyed.

return
true if this object is destroyed
since
JDK1.1

	return destroyed;
    
public voidlist()
Prints information about this thread group to the standard output. This method is useful only for debugging.

since
JDK1.0

	list(System.out, 0);
    
voidlist(java.io.PrintStream out, int indent)

	int ngroupsSnapshot;
	ThreadGroup[] groupsSnapshot;
	synchronized (this) {
	    for (int j = 0 ; j < indent ; j++) {
		out.print(" ");
	    }
	    out.println(this);
	    indent += 4;
	    for (int i = 0 ; i < nthreads ; i++) {
		for (int j = 0 ; j < indent ; j++) {
		    out.print(" ");
		}
		out.println(threads[i]);
	    }
	    ngroupsSnapshot = ngroups;
	    if (groups != null) {
		groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
	    } else {
		groupsSnapshot = null;
	    }
	}
	for (int i = 0 ; i < ngroupsSnapshot ; i++) {
	    groupsSnapshot[i].list(out, indent);
	}
    
public final booleanparentOf(java.lang.ThreadGroup g)
Tests if this thread group is either the thread group argument or one of its ancestor thread groups.

param
g a thread group.
return
true if this thread group is the thread group argument or one of its ancestor thread groups; false otherwise.
since
JDK1.0

	for (; g != null ; g = g.parent) {
	    if (g == this) {
		return true;
	    }
	}
	return false;
    
private voidremove(java.lang.ThreadGroup g)
Removes the specified Thread group from this group.

param
g the Thread group to be removed
return
if this Thread has already been destroyed.

	synchronized (this) {
	    if (destroyed) {
		return;
	    }
	    for (int i = 0 ; i < ngroups ; i++) {
		if (groups[i] == g) {
		    ngroups -= 1;
		    System.arraycopy(groups, i + 1, groups, i, ngroups - i);
		    // Zap dangling reference to the dead group so that
		    // the garbage collector will collect it.
		    groups[ngroups] = null;
		    break;
		}
	    }
	    if (nthreads == 0) {
		notifyAll();
	    }
            if (daemon && (nthreads == 0) &&  
                (nUnstartedThreads == 0) && (ngroups == 0))  
            { 
		destroy();
	    }
	}
    
voidremove(java.lang.Thread t)
Removes the specified Thread from this group.

param
t the Thread to be removed
return
if the Thread has already been destroyed.

	synchronized (this) {
	    if (destroyed) {
		return;
	    }
	    for (int i = 0 ; i < nthreads ; i++) {
		if (threads[i] == t) {
		    System.arraycopy(threads, i + 1, threads, i, --nthreads - i);
		    // Zap dangling reference to the dead thread so that
		    // the garbage collector will collect it.
		    threads[nthreads] = null;
		    break;
		}
	    }
	    if (nthreads == 0) {
		notifyAll();
	    }
            if (daemon && (nthreads == 0) &&  
                (nUnstartedThreads == 0) && (ngroups == 0))  
            { 
		destroy();
	    }
	}
    
public final voidresume()
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.

exception
SecurityException if the current thread is not allowed to access this thread group or any of the threads in the thread group.
see
java.lang.SecurityException
see
java.lang.Thread#resume()
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0
deprecated
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 {@link Thread#suspend} for details.

	int ngroupsSnapshot;
	ThreadGroup[] groupsSnapshot;
	synchronized (this) {
	    checkAccess();
	    for (int i = 0 ; i < nthreads ; i++) {
		threads[i].resume();
	    }
	    ngroupsSnapshot = ngroups;
	    if (groups != null) {
		groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
	    } else {
		groupsSnapshot = null;
	    }
	}
	for (int i = 0 ; i < ngroupsSnapshot ; i++) {
	    groupsSnapshot[i].resume();
	}
    
public final voidsetDaemon(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.

param
daemon if true, marks this thread group as a daemon thread group; otherwise, marks this thread group as normal.
exception
SecurityException if the current thread cannot modify this thread group.
see
java.lang.SecurityException
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

	checkAccess();
	this.daemon = daemon;
    
public final voidsetMaxPriority(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 {@link Thread#MIN_PRIORITY} or greater than {@link 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.

param
pri the new priority of the thread group.
exception
SecurityException if the current thread cannot modify this thread group.
see
#getMaxPriority
see
java.lang.SecurityException
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0

	int ngroupsSnapshot;
	ThreadGroup[] groupsSnapshot;
	synchronized (this) {
	    checkAccess();
	    if (pri < Thread.MIN_PRIORITY) {
		maxPriority = Thread.MIN_PRIORITY;
	    } else if (pri < maxPriority) {
		maxPriority = pri;
	    }
	    ngroupsSnapshot = ngroups;
	    if (groups != null) {
                groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
	    } else {
		groupsSnapshot = null;
	    }
	}
	for (int i = 0 ; i < ngroupsSnapshot ; i++) {
	    groupsSnapshot[i].setMaxPriority(pri);
	}
    
public final voidstop()
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.

exception
SecurityException if the current thread is not allowed to access this thread group or any of the threads in the thread group.
see
java.lang.SecurityException
see
java.lang.Thread#stop()
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0
deprecated
This method is inherently unsafe. See {@link Thread#stop} for details.

        if (stopOrSuspend(false))
            Thread.currentThread().stop();
    
private booleanstopOrSuspend(boolean suspend)
Helper method: recursively stops or suspends (as directed by the boolean argument) all of the threads in this thread group and its subgroups, except the current thread. This method returns true if (and only if) the current thread is found to be in this thread group or one of its subgroups.

        boolean suicide = false;
        Thread us = Thread.currentThread();
	int ngroupsSnapshot;
	ThreadGroup[] groupsSnapshot = null;
	synchronized (this) {
	    checkAccess();
	    for (int i = 0 ; i < nthreads ; i++) {
                if (threads[i]==us)
                    suicide = true;
                else if (suspend)
                    threads[i].suspend();
                else
                    threads[i].stop();
	    }

	    ngroupsSnapshot = ngroups;
	    if (groups != null) {
		groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
	    }
	}
	for (int i = 0 ; i < ngroupsSnapshot ; i++)
	    suicide = groupsSnapshot[i].stopOrSuspend(suspend) || suicide;

        return suicide;
    
public final voidsuspend()
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.

exception
SecurityException if the current thread is not allowed to access this thread group or any of the threads in the thread group.
see
java.lang.Thread#suspend()
see
java.lang.SecurityException
see
java.lang.ThreadGroup#checkAccess()
since
JDK1.0
deprecated
This method is inherently deadlock-prone. See {@link Thread#suspend} for details.

        if (stopOrSuspend(true))
            Thread.currentThread().suspend();
    
public java.lang.StringtoString()
Returns a string representation of this Thread group.

return
a string representation of this thread group.
since
JDK1.0

	return getClass().getName() + "[name=" + getName() + ",maxpri=" + maxPriority + "]";
    
public voiduncaughtException(java.lang.Thread t, java.lang.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 {@link 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 {@linkplain Thread#getDefaultUncaughtExceptionHandler 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 {@link ThreadDeath}. If so, nothing special is done. Otherwise, a message containing the thread's name, as returned from the thread's {@link Thread#getName getName} method, and a stack backtrace, using the Throwable's {@link Throwable#printStackTrace printStackTrace} method, is printed to the {@linkplain System#err standard error stream}.

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

param
t the thread that is about to exit.
param
e the uncaught exception.
since
JDK1.0

	if (parent != null) {
	    parent.uncaughtException(t, e);
	} else {
            Thread.UncaughtExceptionHandler ueh = 
                Thread.getDefaultUncaughtExceptionHandler();
            if (ueh != null) {
                ueh.uncaughtException(t, e);
            } else if (!(e instanceof ThreadDeath)) {
		System.err.print("Exception in thread \""
				 + t.getName() + "\" ");
                e.printStackTrace(System.err);
            }
        }