java.lang
Class Thread

java.lang.Object
  extended by java.lang.Thread
All Implemented Interfaces:
Runnable

public class Thread
extends Object
implements Runnable

Thread represents a single thread of execution in the VM. When an application VM starts up, it creates a non-daemon Thread which calls the main() method of a particular class. There may be other Threads running, such as the garbage collection thread.

Threads have names to identify them. These names are not necessarily unique. Every Thread has a priority, as well, which tells the VM which Threads should get more running time. New threads inherit the priority and daemon status of the parent thread, by default.

There are two methods of creating a Thread: you may subclass Thread and implement the run() method, at which point you may start the Thread by calling its start() method, or you may implement Runnable in the class you want to use and then call new Thread(your_obj).start().

The virtual machine runs until all non-daemon threads have died (either by returning from the run() method as invoked by start(), or by throwing an uncaught exception); or until System.exit is called with adequate permissions.

It is unclear at what point a Thread should be added to a ThreadGroup, and at what point it should be removed. Should it be inserted when it starts, or when it is created? Should it be removed when it is suspended or interrupted? The only thing that is clear is that the Thread should be removed when it is stopped.

Since:
1.0
See Also:
Runnable, Runtime.exit(int), run(), start(), ThreadLocal

Nested Class Summary
static class Thread.State
           Represents the current state of a thread, according to the VM rather than the operating system.
static interface Thread.UncaughtExceptionHandler
           This interface is used to handle uncaught exceptions which cause a Thread to terminate.
 
Field Summary
static int MAX_PRIORITY
          The maximum priority for a Thread.
static int MIN_PRIORITY
          The minimum priority for a Thread.
static int NORM_PRIORITY
          The priority a Thread gets by default.
 
Constructor Summary
Thread()
          Allocates a new Thread object.
Thread(Runnable target)
          Allocates a new Thread object.
Thread(Runnable target, String name)
          Allocates a new Thread object.
Thread(String name)
          Allocates a new Thread object.
Thread(ThreadGroup group, Runnable target)
          Allocates a new Thread object.
Thread(ThreadGroup group, Runnable target, String name)
          Allocate a new Thread object, with the specified ThreadGroup and name, and using the specified Runnable object's run() method to execute.
Thread(ThreadGroup group, Runnable target, String name, long size)
          Allocate a new Thread object, as if by Thread(group, null, name), and give it the specified stack size, in bytes.
Thread(ThreadGroup group, String name)
          Allocates a new Thread object.
 
Method Summary
static int activeCount()
          Get the number of active threads in the current Thread's ThreadGroup.
 void checkAccess()
          Check whether the current Thread is allowed to modify this Thread.
 int countStackFrames()
          Deprecated. pointless, since suspend is deprecated
static Thread currentThread()
          Get the currently executing Thread.
 void destroy()
          Deprecated. This method was originally intended to simply destroy the thread without performing any form of cleanup operation. However, it was never implemented. It is now deprecated for the same reason as suspend(), stop() and resume(); namely, it is prone to deadlocks. If a thread is destroyed while it still maintains a lock on a resource, then this resource will remain locked and any attempts by other threads to access the resource will result in a deadlock. Thus, even an implemented version of this method would be still be deprecated, due to its unsafe nature.
static void dumpStack()
          Print a stack trace of the current thread to stderr using the same format as Throwable's printStackTrace() method.
static int enumerate(Thread[] array)
          Copy every active thread in the current Thread's ThreadGroup into the array.
static Map<Thread,StackTraceElement[]> getAllStackTraces()
           Returns a map of threads to stack traces for each live thread.
 ClassLoader getContextClassLoader()
          Returns the context classloader of this Thread.
static Thread.UncaughtExceptionHandler getDefaultUncaughtExceptionHandler()
          Returns the handler used by default when a thread terminates unexpectedly due to an exception, or null if one doesn't exist.
 long getId()
          Returns the unique identifier for this thread.
 String getName()
          Get this Thread's name.
 int getPriority()
          Get this Thread's priority.
 StackTraceElement[] getStackTrace()
           Returns an array of StackTraceElements representing the current stack trace of this thread.
 Thread.State getState()
          Returns the current state of the thread.
 ThreadGroup getThreadGroup()
          Get the ThreadGroup this Thread belongs to.
 Thread.UncaughtExceptionHandler getUncaughtExceptionHandler()
           Returns the handler used when this thread terminates due to an uncaught exception.
static boolean holdsLock(Object obj)
          Checks whether the current thread holds the monitor on a given object.
 void interrupt()
          Interrupt this Thread.
static boolean interrupted()
          Determine whether the current Thread has been interrupted, and clear the interrupted status in the process.
 boolean isAlive()
          Determine whether this Thread is alive.
 boolean isDaemon()
          Tell whether this is a daemon Thread or not.
 boolean isInterrupted()
          Determine whether the given Thread has been interrupted, but leave the interrupted status alone in the process.
 void join()
          Wait forever for the Thread in question to die.
 void join(long ms)
          Wait the specified amount of time for the Thread in question to die.
 void join(long ms, int ns)
          Wait the specified amount of time for the Thread in question to die.
 void resume()
          Deprecated. pointless, since suspend is deprecated
 void run()
          The method of Thread that will be run if there is no Runnable object associated with the Thread.
 void setContextClassLoader(ClassLoader classloader)
          Sets the context classloader for this Thread.
 void setDaemon(boolean daemon)
          Set the daemon status of this Thread.
static void setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h)
           Sets the default uncaught exception handler used when one isn't provided by the thread or its associated ThreadGroup.
 void setName(String name)
          Set this Thread's name.
 void setPriority(int newPriority)
          Set this Thread's priority.
 void setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h)
          Assigns the given UncaughtExceptionHandler to this thread.
static void sleep(long ms)
          Suspend the current Thread's execution for the specified amount of time.
static void sleep(long timeout, int nanos)
          Suspend the current Thread's execution for the specified amount of time.
 void start()
          Start this Thread, calling the run() method of the Runnable this Thread was created with, or else the run() method of the Thread itself.
 void stop()
          Deprecated. unsafe operation, try not to use
 void stop(Throwable t)
          Deprecated. unsafe operation, try not to use
 void suspend()
          Deprecated. unsafe operation, try not to use
 String toString()
          Returns a string representation of this thread, including the thread's name, priority, and thread group.
static void yield()
          Yield to another thread.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

MIN_PRIORITY

public static final int MIN_PRIORITY
The minimum priority for a Thread.

See Also:
Constant Field Values

NORM_PRIORITY

public static final int NORM_PRIORITY
The priority a Thread gets by default.

See Also:
Constant Field Values

MAX_PRIORITY

public static final int MAX_PRIORITY
The maximum priority for a Thread.

See Also:
Constant Field Values
Constructor Detail

Thread

public Thread()
Allocates a new Thread object. This constructor has the same effect as Thread(null, null, gname), where gname is a newly generated name. Automatically generated names are of the form "Thread-"+n, where n is an integer.

Threads created this way must have overridden their run() method to actually do anything. An example illustrating this method being used follows:

     import java.lang.*;

     class plain01 implements Runnable {
         String name;
         plain01() {
             name = null;
         }
         plain01(String s) {
             name = s;
         }
         public void run() {
             if (name == null)
                 System.out.println("A new thread created");
             else
                 System.out.println("A new thread with name " + name +
                                    " created");
         }
     }
     class threadtest01 {
         public static void main(String args[] ) {
             int failed = 0 ;

             Thread t1 = new Thread();
             if (t1 != null)
                 System.out.println("new Thread() succeed");
             else {
                 System.out.println("new Thread() failed");
                 failed++;
             }
         }
     }
 

See Also:
Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

public Thread(Runnable target)
Allocates a new Thread object. This constructor has the same effect as Thread(null, target, gname), where gname is a newly generated name. Automatically generated names are of the form "Thread-"+n, where n is an integer.

Parameters:
target - the object whose run method is called.
See Also:
Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

public Thread(String name)
Allocates a new Thread object. This constructor has the same effect as Thread(null, null, name).

Parameters:
name - the name of the new thread.
See Also:
Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

public Thread(ThreadGroup group,
              Runnable target)
Allocates a new Thread object. This constructor has the same effect as Thread(group, target, gname), where gname is a newly generated name. Automatically generated names are of the form "Thread-"+n, where n is an integer.

Parameters:
group - the group to put the Thread into
target - the Runnable object to execute
Throws:
SecurityException - if this thread cannot access group
IllegalThreadStateException - if group is destroyed
See Also:
Thread(ThreadGroup, Runnable, String)

Thread

public Thread(ThreadGroup group,
              String name)
Allocates a new Thread object. This constructor has the same effect as Thread(group, null, name)

Parameters:
group - the group to put the Thread into
name - the name for the Thread
Throws:
NullPointerException - if name is null
SecurityException - if this thread cannot access group
IllegalThreadStateException - if group is destroyed
See Also:
Thread(ThreadGroup, Runnable, String)

Thread

public Thread(Runnable target,
              String name)
Allocates a new Thread object. This constructor has the same effect as Thread(null, target, name).

Parameters:
target - the Runnable object to execute
name - the name for the Thread
Throws:
NullPointerException - if name is null
See Also:
Thread(ThreadGroup, Runnable, String)

Thread

public Thread(ThreadGroup group,
              Runnable target,
              String name)
Allocate a new Thread object, with the specified ThreadGroup and name, and using the specified Runnable object's run() method to execute. If the Runnable object is null, this (which is a Runnable) is used instead.

If the ThreadGroup is null, the security manager is checked. If a manager exists and returns a non-null object for getThreadGroup, that group is used; otherwise the group of the creating thread is used. Note that the security manager calls checkAccess if the ThreadGroup is not null.

The new Thread will inherit its creator's priority and daemon status. These can be changed with setPriority and setDaemon.

Parameters:
group - the group to put the Thread into
target - the Runnable object to execute
name - the name for the Thread
Throws:
NullPointerException - if name is null
SecurityException - if this thread cannot access group
IllegalThreadStateException - if group is destroyed
See Also:
Runnable.run(), run(), setDaemon(boolean), setPriority(int), SecurityManager.checkAccess(ThreadGroup), ThreadGroup.checkAccess()

Thread

public Thread(ThreadGroup group,
              Runnable target,
              String name,
              long size)
Allocate a new Thread object, as if by Thread(group, null, name), and give it the specified stack size, in bytes. The stack size is highly platform independent, and the virtual machine is free to round up or down, or ignore it completely. A higher value might let you go longer before a StackOverflowError, while a lower value might let you go longer before an OutOfMemoryError. Or, it may do absolutely nothing! So be careful, and expect to need to tune this value if your virtual machine even supports it.

Parameters:
group - the group to put the Thread into
target - the Runnable object to execute
name - the name for the Thread
size - the stack size, in bytes; 0 to be ignored
Throws:
NullPointerException - if name is null
SecurityException - if this thread cannot access group
IllegalThreadStateException - if group is destroyed
Since:
1.4
Method Detail

activeCount

public static int activeCount()
Get the number of active threads in the current Thread's ThreadGroup. This implementation calls currentThread().getThreadGroup().activeCount().

Returns:
the number of active threads in the current ThreadGroup
See Also:
ThreadGroup.activeCount()

checkAccess

public final void checkAccess()
Check whether the current Thread is allowed to modify this Thread. This passes the check on to SecurityManager.checkAccess(this).

Throws:
SecurityException - if the current Thread cannot modify this Thread
See Also:
SecurityManager.checkAccess(Thread)

countStackFrames

public int countStackFrames()
Deprecated. pointless, since suspend is deprecated

Count the number of stack frames in this Thread. The Thread in question must be suspended when this occurs.

Returns:
the number of stack frames in this Thread
Throws:
IllegalThreadStateException - if this Thread is not suspended

currentThread

public static Thread currentThread()
Get the currently executing Thread. In the situation that the currently running thread was created by native code and doesn't have an associated Thread object yet, a new Thread object is constructed and associated with the native thread.

Returns:
the currently executing Thread

destroy

public void destroy()
Deprecated. This method was originally intended to simply destroy the thread without performing any form of cleanup operation. However, it was never implemented. It is now deprecated for the same reason as suspend(), stop() and resume(); namely, it is prone to deadlocks. If a thread is destroyed while it still maintains a lock on a resource, then this resource will remain locked and any attempts by other threads to access the resource will result in a deadlock. Thus, even an implemented version of this method would be still be deprecated, due to its unsafe nature.

Originally intended to destroy this thread, this method was never implemented by Sun, and is hence a no-op.

Throws:
NoSuchMethodError - as this method was never implemented.

dumpStack

public static void dumpStack()
Print a stack trace of the current thread to stderr using the same format as Throwable's printStackTrace() method.

See Also:
Throwable.printStackTrace()

enumerate

public static int enumerate(Thread[] array)
Copy every active thread in the current Thread's ThreadGroup into the array. Extra threads are silently ignored. This implementation calls getThreadGroup().enumerate(array), which may have a security check, checkAccess(group).

Parameters:
array - the array to place the Threads into
Returns:
the number of Threads placed into the array
Throws:
NullPointerException - if array is null
SecurityException - if you cannot access the ThreadGroup
See Also:
ThreadGroup.enumerate(Thread[]), activeCount(), SecurityManager.checkAccess(ThreadGroup)

getName

public final String getName()
Get this Thread's name.

Returns:
this Thread's name

getPriority

public final int getPriority()
Get this Thread's priority.

Returns:
the Thread's priority

getThreadGroup

public final ThreadGroup getThreadGroup()
Get the ThreadGroup this Thread belongs to. If the thread has died, this returns null.

Returns:
this Thread's ThreadGroup

holdsLock

public static boolean holdsLock(Object obj)
Checks whether the current thread holds the monitor on a given object. This allows you to do assert Thread.holdsLock(obj).

Parameters:
obj - the object to test lock ownership on.
Returns:
true if the current thread is currently synchronized on obj
Throws:
NullPointerException - if obj is null
Since:
1.4

interrupt

public void interrupt()
Interrupt this Thread. First, there is a security check, checkAccess. Then, depending on the current state of the thread, various actions take place:

If the thread is waiting because of Object.wait(), sleep(long), or join(), its interrupt status will be cleared, and an InterruptedException will be thrown. Notice that this case is only possible if an external thread called interrupt().

If the thread is blocked in an interruptible I/O operation, in InterruptibleChannel, the interrupt status will be set, and ClosedByInterruptException will be thrown.

If the thread is blocked on a Selector, the interrupt status will be set, and the selection will return, with a possible non-zero value, as though by the wakeup() method.

Otherwise, the interrupt status will be set.

Throws:
SecurityException - if you cannot modify this Thread

interrupted

public static boolean interrupted()
Determine whether the current Thread has been interrupted, and clear the interrupted status in the process.

Returns:
whether the current Thread has been interrupted
See Also:
isInterrupted()

isInterrupted

public boolean isInterrupted()
Determine whether the given Thread has been interrupted, but leave the interrupted status alone in the process.

Returns:
whether the Thread has been interrupted
See Also:
interrupted()

isAlive

public final boolean isAlive()
Determine whether this Thread is alive. A thread which is alive has started and not yet died.

Returns:
whether this Thread is alive

isDaemon

public final boolean isDaemon()
Tell whether this is a daemon Thread or not.

Returns:
whether this is a daemon Thread or not
See Also:
setDaemon(boolean)

join

public final void join()
                throws InterruptedException
Wait forever for the Thread in question to die.

Throws:
InterruptedException - if the Thread is interrupted; it's interrupted status will be cleared

join

public final void join(long ms)
                throws InterruptedException
Wait the specified amount of time for the Thread in question to die.

Parameters:
ms - the number of milliseconds to wait, or 0 for forever
Throws:
InterruptedException - if the Thread is interrupted; it's interrupted status will be cleared

join

public final void join(long ms,
                       int ns)
                throws InterruptedException
Wait the specified amount of time for the Thread in question to die.

Note that 1,000,000 nanoseconds == 1 millisecond, but most VMs do not offer that fine a grain of timing resolution. Besides, there is no guarantee that this thread can start up immediately when time expires, because some other thread may be active. So don't expect real-time performance.

Parameters:
ms - the number of milliseconds to wait, or 0 for forever
ns - the number of extra nanoseconds to sleep (0-999999)
Throws:
InterruptedException - if the Thread is interrupted; it's interrupted status will be cleared
IllegalArgumentException - if ns is invalid

resume

public final void resume()
Deprecated. pointless, since suspend is deprecated

Resume this Thread. If the thread is not suspended, this method does nothing. To mirror suspend(), there may be a security check: checkAccess.

Throws:
SecurityException - if you cannot resume the Thread
See Also:
checkAccess(), suspend()

run

public void run()
The method of Thread that will be run if there is no Runnable object associated with the Thread. Thread's implementation does nothing at all.

Specified by:
run in interface Runnable
See Also:
start(), Thread(ThreadGroup, Runnable, String)

setDaemon

public final void setDaemon(boolean daemon)
Set the daemon status of this Thread. If this is a daemon Thread, then the VM may exit even if it is still running. This may only be called before the Thread starts running. There may be a security check, checkAccess.

Parameters:
daemon - whether this should be a daemon thread or not
Throws:
SecurityException - if you cannot modify this Thread
IllegalThreadStateException - if the Thread is active
See Also:
isDaemon(), checkAccess()

getContextClassLoader

public ClassLoader getContextClassLoader()
Returns the context classloader of this Thread. The context classloader can be used by code that want to load classes depending on the current thread. Normally classes are loaded depending on the classloader of the current class. There may be a security check for RuntimePermission("getClassLoader") if the caller's class loader is not null or an ancestor of this thread's context class loader.

Returns:
the context class loader
Throws:
SecurityException - when permission is denied
Since:
1.2
See Also:
setContextClassLoader(ClassLoader)

setContextClassLoader

public void setContextClassLoader(ClassLoader classloader)
Sets the context classloader for this Thread. When not explicitly set, the context classloader for a thread is the same as the context classloader of the thread that created this thread. The first thread has as context classloader the system classloader. There may be a security check for RuntimePermission("setContextClassLoader").

Parameters:
classloader - the new context class loader
Throws:
SecurityException - when permission is denied
Since:
1.2
See Also:
getContextClassLoader()

setName

public final void setName(String name)
Set this Thread's name. There may be a security check, checkAccess.

Parameters:
name - the new name for this Thread
Throws:
NullPointerException - if name is null
SecurityException - if you cannot modify this Thread

yield

public static void yield()
Yield to another thread. The Thread will not lose any locks it holds during this time. There are no guarantees which thread will be next to run, and it could even be this one, but most VMs will choose the highest priority thread that has been waiting longest.


sleep

public static void sleep(long ms)
                  throws InterruptedException
Suspend the current Thread's execution for the specified amount of time. The Thread will not lose any locks it has during this time. There are no guarantees which thread will be next to run, but most VMs will choose the highest priority thread that has been waiting longest.

Parameters:
ms - the number of milliseconds to sleep, or 0 for forever
Throws:
InterruptedException - if the Thread is (or was) interrupted; it's interrupted status will be cleared
IllegalArgumentException - if ms is negative
See Also:
interrupt(), Object.notify(), Object.wait(long)

sleep

public static void sleep(long timeout,
                         int nanos)
                  throws InterruptedException
Suspend the current Thread's execution for the specified amount of time. The Thread will not lose any locks it has during this time. There are no guarantees which thread will be next to run, but most VMs will choose the highest priority thread that has been waiting longest.

Note that 1,000,000 nanoseconds == 1 millisecond, but most VMs do not offer that fine a grain of timing resolution. When ms is zero and ns is non-zero the Thread will sleep for at least one milli second. There is no guarantee that this thread can start up immediately when time expires, because some other thread may be active. So don't expect real-time performance.

Parameters:
ms - the number of milliseconds to sleep, or 0 for forever
ns - the number of extra nanoseconds to sleep (0-999999)
Throws:
InterruptedException - if the Thread is (or was) interrupted; it's interrupted status will be cleared
IllegalArgumentException - if ms or ns is negative or ns is larger than 999999.
See Also:
interrupt(), Object.notify(), Object.wait(long, int)

start

public void start()
Start this Thread, calling the run() method of the Runnable this Thread was created with, or else the run() method of the Thread itself. This is the only way to start a new thread; calling run by yourself will just stay in the same thread. The virtual machine will remove the thread from its thread group when the run() method completes.

Throws:
IllegalThreadStateException - if the thread has already started
See Also:
run()

stop

public final void stop()
Deprecated. unsafe operation, try not to use

Cause this Thread to stop abnormally because of the throw of a ThreadDeath error. If you stop a Thread that has not yet started, it will stop immediately when it is actually started.

This is inherently unsafe, as it can interrupt synchronized blocks and leave data in bad states. Hence, there is a security check: checkAccess(this), plus another one if the current thread is not this: RuntimePermission("stopThread"). If you must catch a ThreadDeath, be sure to rethrow it after you have cleaned up. ThreadDeath is the only exception which does not print a stack trace when the thread dies.

Throws:
SecurityException - if you cannot stop the Thread
See Also:
interrupt(), checkAccess(), start(), ThreadDeath, ThreadGroup.uncaughtException(Thread, Throwable), SecurityManager.checkAccess(Thread), SecurityManager.checkPermission(Permission)

stop

public final void stop(Throwable t)
Deprecated. unsafe operation, try not to use

Cause this Thread to stop abnormally and throw the specified exception. If you stop a Thread that has not yet started, the stop is ignored (contrary to what the JDK documentation says). WARNINGThis bypasses Java security, and can throw a checked exception which the call stack is unprepared to handle. Do not abuse this power.

This is inherently unsafe, as it can interrupt synchronized blocks and leave data in bad states. Hence, there is a security check: checkAccess(this), plus another one if the current thread is not this: RuntimePermission("stopThread"). If you must catch a ThreadDeath, be sure to rethrow it after you have cleaned up. ThreadDeath is the only exception which does not print a stack trace when the thread dies.

Parameters:
t - the Throwable to throw when the Thread dies
Throws:
SecurityException - if you cannot stop the Thread
NullPointerException - in the calling thread, if t is null
See Also:
interrupt(), checkAccess(), start(), ThreadDeath, ThreadGroup.uncaughtException(Thread, Throwable), SecurityManager.checkAccess(Thread), SecurityManager.checkPermission(Permission)

suspend

public final void suspend()
Deprecated. unsafe operation, try not to use

Suspend this Thread. It will not come back, ever, unless it is resumed.

This is inherently unsafe, as the suspended thread still holds locks, and can potentially deadlock your program. Hence, there is a security check: checkAccess.

Throws:
SecurityException - if you cannot suspend the Thread
See Also:
checkAccess(), resume()

setPriority

public final void setPriority(int newPriority)
Set this Thread's priority. There may be a security check, checkAccess, then the priority is set to the smaller of priority and the ThreadGroup maximum priority.

Parameters:
priority - the new priority for this Thread
Throws:
IllegalArgumentException - if priority exceeds MIN_PRIORITY or MAX_PRIORITY
SecurityException - if you cannot modify this Thread
See Also:
getPriority(), checkAccess(), ThreadGroup.getMaxPriority(), MIN_PRIORITY, MAX_PRIORITY

toString

public String toString()
Returns a string representation of this thread, including the thread's name, priority, and thread group.

Overrides:
toString in class Object
Returns:
a human-readable String representing this Thread
See Also:
Object.getClass(), Object.hashCode(), Class.getName(), Integer.toHexString(int)

setUncaughtExceptionHandler

public void setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h)
Assigns the given UncaughtExceptionHandler to this thread. This will then be called if the thread terminates due to an uncaught exception, pre-empting that of the ThreadGroup.

Parameters:
h - the handler to use for this thread.
Throws:
SecurityException - if the current thread can't modify this thread.
Since:
1.5

getUncaughtExceptionHandler

public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler()

Returns the handler used when this thread terminates due to an uncaught exception. The handler used is determined by the following:

Returns:
the appropriate UncaughtExceptionHandler or null if one can't be obtained.
Since:
1.5

setDefaultUncaughtExceptionHandler

public static void setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h)

Sets the default uncaught exception handler used when one isn't provided by the thread or its associated ThreadGroup. This exception handler is used when the thread itself does not have an exception handler, and the thread's ThreadGroup does not override this default mechanism with its own. As the group calls this handler by default, this exception handler should not defer to that of the group, as it may lead to infinite recursion.

Uncaught exception handlers are used when a thread terminates due to an uncaught exception. Replacing this handler allows default code to be put in place for all threads in order to handle this eventuality.

Parameters:
h - the new default uncaught exception handler to use.
Throws:
SecurityException - if a security manager is present and disallows the runtime permission "setDefaultUncaughtExceptionHandler".
Since:
1.5

getDefaultUncaughtExceptionHandler

public static Thread.UncaughtExceptionHandler getDefaultUncaughtExceptionHandler()
Returns the handler used by default when a thread terminates unexpectedly due to an exception, or null if one doesn't exist.

Returns:
the default uncaught exception handler.
Since:
1.5

getId

public long getId()
Returns the unique identifier for this thread. This ID is generated on thread creation, and may be re-used on its death.

Returns:
a positive long number representing the thread's ID.
Since:
1.5

getState

public Thread.State getState()
Returns the current state of the thread. This is designed for monitoring thread behaviour, rather than for synchronization control.

Returns:
the current thread state.

getAllStackTraces

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

Returns a map of threads to stack traces for each live thread. The keys of the map are Thread objects, which map to arrays of StackTraceElements. The results obtained from Calling this method are equivalent to calling getStackTrace() on each thread in succession. Threads may be executing while this takes place, and the results represent a snapshot of the thread at the time its getStackTrace() method is called.

The stack trace information contains the methods called by the thread, with the most recent method forming the first element in the array. The array will be empty if the virtual machine can not obtain information on the thread.

To execute this method, the current security manager (if one exists) must allow both the "getStackTrace" and "modifyThreadGroup" RuntimePermissions.

Returns:
a map of threads to arrays of StackTraceElements.
Throws:
SecurityException - if a security manager exists, and prevents either or both the runtime permissions specified above.
Since:
1.5
See Also:
getStackTrace()

getStackTrace

public StackTraceElement[] getStackTrace()

Returns an array of StackTraceElements representing the current stack trace of this thread. The first element of the array is the most recent method called, and represents the top of the stack. The elements continue in this order, with the last element representing the bottom of the stack.

A zero element array is returned for threads which have not yet started (and thus have not yet executed any methods) or for those which have terminated. Where the virtual machine can not obtain a trace for the thread, an empty array is also returned. The virtual machine may also omit some methods from the trace in non-zero arrays.

To execute this method, the current security manager (if one exists) must allow both the "getStackTrace" and "modifyThreadGroup" RuntimePermissions.

Returns:
a stack trace for this thread.
Throws:
SecurityException - if a security manager exists, and prevents the use of the "getStackTrace" permission.
Since:
1.5
See Also:
getAllStackTraces()