Thread (Java Platform SE 6)

A thread is a thread of execution in a program. The Java Virtual Machine allows an application to have multiple threads of execution running concurrently.

Every thread has a priority. Threads with higher priority are executed in preference to threads with lower priority. Each thread may or may not also be marked as a daemon. When code running in some thread creates a new Thread object, the new thread has its priority initially set equal to the priority of the creating thread, and is a daemon thread if and only if the creating thread is a daemon.

When a Java Virtual Machine starts up, there is usually a single non-daemon thread (which typically calls the method named main of some designated class). The Java Virtual Machine continues to execute threads until either of the following occurs:

The exit method of class Runtime has been called and the security manager has permitted the exit operation to take place.
All threads that are not daemon threads have died, either by returning from the call to the run method or by throwing an exception that propagates beyond the run method.

There are two ways to create a new thread of execution. One is to declare a class to be a subclass of Thread. This subclass should override the run method of class Thread. An instance of the subclass can then be allocated and started. For example, a thread that computes primes larger than a stated value could be written as follows:

     class PrimeThread extends Thread {
         long minPrime;
         PrimeThread(long minPrime) {
             this.minPrime = minPrime;
         }
 
         public void run() {
             // compute primes larger than minPrime
              . . .
         }
     }

The following code would then create a thread and start it running:

     PrimeThread p = new PrimeThread(143);
     p.start();

The other way to create a thread is to declare a class that implements the Runnable interface. That class then implements the run method. An instance of the class can then be allocated, passed as an argument when creating Thread, and started. The same example in this other style looks like the following:

     class PrimeRun implements Runnable {
         long minPrime;
         PrimeRun(long minPrime) {
             this.minPrime = minPrime;
         }
 
         public void run() {
             // compute primes larger than minPrime
              . . .
         }
     }

The following code would then create a thread and start it running:

     PrimeRun p = new PrimeRun(143);
     new Thread(p).start();

Every thread has a name for identification purposes. More than one thread may have the same name. If a name is not specified when a thread is created, a new name is generated for it.

Since:: JDK1.0
See Also:: Runnable, Runtime.exit(int), run(), stop()

Nested Class Summary
`static class`	`Thread.State` A thread state.
`static interface`	`Thread.UncaughtExceptionHandler` Interface for handlers invoked when a `Thread` abruptly terminates due to an uncaught exception.

Field Summary
`static int`	`MAX_PRIORITY` The maximum priority that a thread can have.
`static int`	`MIN_PRIORITY` The minimum priority that a thread can have.
`static int`	`NORM_PRIORITY` The default priority that is assigned to a thread.

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)` Allocates a new `Thread` object so that it has `target` as its run object, has the specified `name` as its name, and belongs to the thread group referred to by `group`.
`Thread(ThreadGroup group, Runnable target, String name, long stackSize)` Allocates a new `Thread` object so that it has `target` as its run object, has the specified `name` as its name, belongs to the thread group referred to by `group`, and has the specified stack size.
`Thread(ThreadGroup group, String name)` Allocates a new `Thread` object.

Method Summary
`static int`	`activeCount()` Returns the number of active threads in the current thread's thread group.
`void`	`checkAccess()` Determines if the currently running thread has permission to modify this thread.
`int`	`countStackFrames()` Deprecated. The definition of this call depends on `suspend()`, which is deprecated. Further, the results of this call were never well-defined.
`static Thread`	`currentThread()` Returns a reference to the currently executing thread object.
`void`	`destroy()` Deprecated. This method was originally designed to destroy this thread without any cleanup. Any monitors it held would have remained locked. However, the method was never implemented. If if were to be implemented, it would be deadlock-prone in much the manner of `suspend()`. If the target thread held a lock protecting a critical system resource when it was destroyed, no thread could ever access this resource again. If another thread ever attempted to lock this resource, deadlock would result. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
`static void`	`dumpStack()` Prints a stack trace of the current thread to the standard error stream.
`static int`	`enumerate(Thread[] tarray)` Copies into the specified array every active thread in the current thread's thread group and its subgroups.
`static Map<Thread,StackTraceElement[]>`	`getAllStackTraces()` Returns a map of stack traces for all live threads.
`ClassLoader`	`getContextClassLoader()` Returns the context ClassLoader for this Thread.
`static Thread.UncaughtExceptionHandler`	`getDefaultUncaughtExceptionHandler()` Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception.
`long`	`getId()` Returns the identifier of this Thread.
`String`	`getName()` Returns this thread's name.
`int`	`getPriority()` Returns this thread's priority.
`StackTraceElement[]`	`getStackTrace()` Returns an array of stack trace elements representing the stack dump of this thread.
`Thread.State`	`getState()` Returns the state of this thread.
`ThreadGroup`	`getThreadGroup()` Returns the thread group to which this thread belongs.
`Thread.UncaughtExceptionHandler`	`getUncaughtExceptionHandler()` Returns the handler invoked when this thread abruptly terminates due to an uncaught exception.
`static boolean`	`holdsLock(Object obj)` Returns `true` if and only if the current thread holds the monitor lock on the specified object.
`void`	`interrupt()` Interrupts this thread.
`static boolean`	`interrupted()` Tests whether the current thread has been interrupted.
`boolean`	`isAlive()` Tests if this thread is alive.
`boolean`	`isDaemon()` Tests if this thread is a daemon thread.
`boolean`	`isInterrupted()` Tests whether this thread has been interrupted.
`void`	`join()` Waits for this thread to die.
`void`	`join(long millis)` Waits at most `millis` milliseconds for this thread to die.
`void`	`join(long millis, int nanos)` Waits at most `millis` milliseconds plus `nanos` nanoseconds for this thread to die.
`void`	`resume()` Deprecated. This method exists solely for use with `suspend()`, which has been deprecated because it is deadlock-prone. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
`void`	`run()` If this thread was constructed using a separate `Runnable` run object, then that `Runnable` object's `run` method is called; otherwise, this method does nothing and returns.
`void`	`setContextClassLoader(ClassLoader cl)` Sets the context ClassLoader for this Thread.
`void`	`setDaemon(boolean on)` Marks this thread as either a daemon thread or a user thread.
`static void`	`setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)` Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread.
`void`	`setName(String name)` Changes the name of this thread to be equal to the argument `name`.
`void`	`setPriority(int newPriority)` Changes the priority of this thread.
`void`	`setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)` Set the handler invoked when this thread abruptly terminates due to an uncaught exception.
`static void`	`sleep(long millis)` Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers.
`static void`	`sleep(long millis, int nanos)` Causes the currently executing thread to sleep (cease execution) for the specified number of milliseconds plus the specified number of nanoseconds, subject to the precision and accuracy of system timers and schedulers.
`void`	`start()` Causes this thread to begin execution; the Java Virtual Machine calls the `run` method of this thread.
`void`	`stop()` Deprecated. This method is inherently unsafe. Stopping a thread with Thread.stop causes it to unlock all of the monitors that it has locked (as a natural consequence of the unchecked `ThreadDeath` exception propagating up the stack). If any of the objects previously protected by these monitors were in an inconsistent state, the damaged objects become visible to other threads, potentially resulting in arbitrary behavior. Many uses of `stop` should be replaced by code that simply modifies some variable to indicate that the target thread should stop running. The target thread should check this variable regularly, and return from its run method in an orderly fashion if the variable indicates that it is to stop running. If the target thread waits for long periods (on a condition variable, for example), the `interrupt` method should be used to interrupt the wait. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
`void`	`stop(Throwable obj)` Deprecated. This method is inherently unsafe. See `stop()` for details. An additional danger of this method is that it may be used to generate exceptions that the target thread is unprepared to handle (including checked exceptions that the thread could not possibly throw, were it not for this method). For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
`void`	`suspend()` Deprecated. This method has been deprecated, as it is inherently deadlock-prone. If the target thread holds a lock on the monitor protecting a critical system resource when it is suspended, no thread can access this resource until the target thread is resumed. If the thread that would resume the target thread attempts to lock this monitor prior to calling `resume`, deadlock results. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
`String`	`toString()` Returns a string representation of this thread, including the thread's name, priority, and thread group.
`static void`	`yield()` Causes the currently executing thread object to temporarily pause and allow other threads to execute.

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 that a thread can have.

See Also:: Constant Field Values

NORM_PRIORITY

public static final int NORM_PRIORITY

The default priority that is assigned to a thread.

See Also:: Constant Field Values

MAX_PRIORITY

public static final int MAX_PRIORITY

The maximum priority that a thread can have.

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.

See Also:: Thread(ThreadGroup, Runnable, 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(ThreadGroup, Runnable, 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 thread group.; target - the object whose run method is called.
Throws:: SecurityException - if the current thread cannot create a thread in the specified thread group.
See Also:: Thread(ThreadGroup, Runnable, 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(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 thread group.; name - the name of the new thread.
Throws:: SecurityException - if the current thread cannot create a thread in the specified thread group.
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 object whose run method is called.; name - the name of the new thread.
See Also:: Thread(ThreadGroup, Runnable, String)

Thread

public Thread(ThreadGroup group,
              Runnable target,
              String name)

Allocates a new Thread object so that it has target as its run object, has the specified name as its name, and belongs to the thread group referred to by group.

If group is null and there is a security manager, the group is determined by the security manager's getThreadGroup method. If group is null and there is not a security manager, or the security manager's getThreadGroup method returns null, the group is set to be the same ThreadGroup as the thread that is creating the new thread.

If there is a security manager, its checkAccess method is called with the ThreadGroup as its argument.

In addition, its checkPermission method is called with the RuntimePermission("enableContextClassLoaderOverride") permission when invoked directly or indirectly by the constructor of a subclass which overrides the getContextClassLoader or setContextClassLoader methods. This may result in a SecurityException.

If the target argument is not null, the run method of the target is called when this thread is started. If the target argument is null, this thread's run method is called when this thread is started.

The priority of the newly created thread is set equal to the priority of the thread creating it, that is, the currently running thread. The method setPriority may be used to change the priority to a new value.

The newly created thread is initially marked as being a daemon thread if and only if the thread creating it is currently marked as a daemon thread. The method setDaemon may be used to change whether or not a thread is a daemon.

Parameters:: group - the thread group.; target - the object whose run method is called.; name - the name of the new thread.
Throws:: SecurityException - if the current thread cannot create a thread in the specified thread group or cannot override the context class loader methods.
See Also:: Runnable.run(), run(), setDaemon(boolean), setPriority(int), ThreadGroup.checkAccess(), SecurityManager.checkAccess(java.lang.Thread)

Thread

public Thread(ThreadGroup group,
              Runnable target,
              String name,
              long stackSize)

Allocates a new Thread object so that it has target as its run object, has the specified name as its name, belongs to the thread group referred to by group, and has the specified stack size.

This constructor is identical to Thread(ThreadGroup,Runnable,String) with the exception of the fact that it allows the thread stack size to be specified. The stack size is the approximate number of bytes of address space that the virtual machine is to allocate for this thread's stack. The effect of the stackSize parameter, if any, is highly platform dependent.

On some platforms, specifying a higher value for the stackSize parameter may allow a thread to achieve greater recursion depth before throwing a StackOverflowError. Similarly, specifying a lower value may allow a greater number of threads to exist concurrently without throwing an OutOfMemoryError (or other internal error). The details of the relationship between the value of the stackSize parameter and the maximum recursion depth and concurrency level are platform-dependent. On some platforms, the value of the stackSize parameter may have no effect whatsoever.

The virtual machine is free to treat the stackSize parameter as a suggestion. If the specified value is unreasonably low for the platform, the virtual machine may instead use some platform-specific minimum value; if the specified value is unreasonably high, the virtual machine may instead use some platform-specific maximum. Likewise, the virtual machine is free to round the specified value up or down as it sees fit (or to ignore it completely).

Specifying a value of zero for the stackSize parameter will cause this constructor to behave exactly like the Thread(ThreadGroup, Runnable, String) constructor.

Due to the platform-dependent nature of the behavior of this constructor, extreme care should be exercised in its use. The thread stack size necessary to perform a given computation will likely vary from one JRE implementation to another. In light of this variation, careful tuning of the stack size parameter may be required, and the tuning may need to be repeated for each JRE implementation on which an application is to run.

Implementation note: Java platform implementers are encouraged to document their implementation's behavior with respect to the stackSize parameter.

Parameters:: group - the thread group.; target - the object whose run method is called.; name - the name of the new thread.; stackSize - the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored.
Throws:: SecurityException - if the current thread cannot create a thread in the specified thread group.
Since:: 1.4

Method Detail

currentThread

public static Thread currentThread()

Returns a reference to the currently executing thread object.

Returns:: the currently executing thread.

yield

public static void yield()

Causes the currently executing thread object to temporarily pause and allow other threads to execute.

sleep

public static void sleep(long millis)
                  throws InterruptedException

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.

Parameters:: millis - the length of time to sleep in milliseconds.
Throws:: InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
See Also:: Object.notify()

sleep

public static void sleep(long millis,
                         int nanos)
                  throws InterruptedException

Causes the currently executing thread to sleep (cease execution) for the specified number of milliseconds plus the specified number of nanoseconds, subject to the precision and accuracy of system timers and schedulers. The thread does not lose ownership of any monitors.

Parameters:: millis - the length of time to sleep in milliseconds.; nanos - 0-999999 additional nanoseconds to sleep.
Throws:: IllegalArgumentException - if the value of millis is negative or the value of nanos is not in the range 0-999999.; InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
See Also:: Object.notify()

start

public void start()

Causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.

The result is that two threads are running concurrently: the current thread (which returns from the call to the start method) and the other thread (which executes its run method).

It is never legal to start a thread more than once. In particular, a thread may not be restarted once it has completed execution.

Throws:: IllegalThreadStateException - if the thread was already started.
See Also:: run(), stop()

run

public void run()

If this thread was constructed using a separate Runnable run object, then that Runnable object's run method is called; otherwise, this method does nothing and returns.

Subclasses of Thread should override this method.

Specified by:: run in interface Runnable

See Also:: start(), stop(), Thread(ThreadGroup, Runnable, String)

stop

@Deprecated
public final void stop()

Deprecated. This method is inherently unsafe. Stopping a thread with Thread.stop causes it to unlock all of the monitors that it has locked (as a natural consequence of the unchecked ThreadDeath exception propagating up the stack). If any of the objects previously protected by these monitors were in an inconsistent state, the damaged objects become visible to other threads, potentially resulting in arbitrary behavior. Many uses of stop should be replaced by code that simply modifies some variable to indicate that the target thread should stop running. The target thread should check this variable regularly, and return from its run method in an orderly fashion if the variable indicates that it is to stop running. If the target thread waits for long periods (on a condition variable, for example), the interrupt method should be used to interrupt the wait. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.

Forces the thread to stop executing.

If there is a security manager installed, its checkAccess method is called with this as its argument. This may result in a SecurityException being raised (in the current thread).

If this thread is different from the current thread (that is, the current thread is trying to stop a thread other than itself), the security manager's checkPermission method (with a RuntimePermission("stopThread") argument) is called in addition. Again, this may result in throwing a SecurityException (in the current thread).

The thread represented by this thread is forced to stop whatever it is doing abnormally and to throw a newly created ThreadDeath object as an exception.

It is permitted to stop a thread that has not yet been started. If the thread is eventually started, it immediately terminates.

An application should not normally try to catch ThreadDeath unless it must do some extraordinary cleanup operation (note that the throwing of ThreadDeath causes finally clauses of try statements to be executed before the thread officially dies). If a catch clause catches a ThreadDeath object, it is important to rethrow the object so that the thread actually dies.

The top-level error handler that reacts to otherwise uncaught exceptions does not print out a message or otherwise notify the application if the uncaught exception is an instance of ThreadDeath.

Throws:: SecurityException - if the current thread cannot modify this thread.
See Also:: interrupt(), checkAccess(), run(), start(), ThreadDeath, ThreadGroup.uncaughtException(Thread,Throwable), SecurityManager.checkAccess(Thread), SecurityManager.checkPermission(java.security.Permission)

stop

@Deprecated
public final void stop(Throwable obj)

Deprecated. This method is inherently unsafe. See stop() for details. An additional danger of this method is that it may be used to generate exceptions that the target thread is unprepared to handle (including checked exceptions that the thread could not possibly throw, were it not for this method). For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.

Forces the thread to stop executing.

If there is a security manager installed, the checkAccess method of this thread is called, which may result in a SecurityException being raised (in the current thread).

If this thread is different from the current thread (that is, the current thread is trying to stop a thread other than itself) or obj is not an instance of ThreadDeath, the security manager's checkPermission method (with the RuntimePermission("stopThread") argument) is called in addition. Again, this may result in throwing a SecurityException (in the current thread).

If the argument obj is null, a NullPointerException is thrown (in the current thread).

The thread represented by this thread is forced to stop whatever it is doing abnormally and to throw the Throwable object obj as an exception. This is an unusual action to take; normally, the stop method that takes no arguments should be used.

It is permitted to stop a thread that has not yet been started. If the thread is eventually started, it immediately terminates.

Parameters:: obj - the Throwable object to be thrown.
Throws:: SecurityException - if the current thread cannot modify this thread.; NullPointerException - if obj is null.
See Also:: interrupt(), checkAccess(), run(), start(), stop(), SecurityManager.checkAccess(Thread), SecurityManager.checkPermission(java.security.Permission)

interrupt

public void interrupt()

Interrupts this thread.

Unless the current thread is interrupting itself, which is always permitted, the checkAccess method of this thread is invoked, which may cause a SecurityException to be thrown.

If this thread is blocked in an invocation of the wait(), wait(long), or wait(long, int) methods of the Object class, or of the join(), join(long), join(long, int), sleep(long), or sleep(long, int), methods of this class, then its interrupt status will be cleared and it will receive an InterruptedException.

If this thread is blocked in an I/O operation upon an interruptible channel then the channel will be closed, the thread's interrupt status will be set, and the thread will receive a ClosedByInterruptException.

If this thread is blocked in a Selector then the thread's interrupt status will be set and it will return immediately from the selection operation, possibly with a non-zero value, just as if the selector's wakeup method were invoked.

If none of the previous conditions hold then this thread's interrupt status will be set.

Interrupting a thread that is not alive need not have any effect.

Throws:: SecurityException - if the current thread cannot modify this thread

interrupted

public static boolean interrupted()

Tests whether the current thread has been interrupted. The interrupted status of the thread is cleared by this method. In other words, if this method were to be called twice in succession, the second call would return false (unless the current thread were interrupted again, after the first call had cleared its interrupted status and before the second call had examined it).

A thread interruption ignored because a thread was not alive at the time of the interrupt will be reflected by this method returning false.

Returns:: true if the current thread has been interrupted; false otherwise.
See Also:: isInterrupted()

isInterrupted

public boolean isInterrupted()

Tests whether this thread has been interrupted. The interrupted status of the thread is unaffected by this method.

A thread interruption ignored because a thread was not alive at the time of the interrupt will be reflected by this method returning false.

Returns:: true if this thread has been interrupted; false otherwise.
See Also:: interrupted()

destroy

@Deprecated
public void destroy()

Deprecated. This method was originally designed to destroy this thread without any cleanup. Any monitors it held would have remained locked. However, the method was never implemented. If if were to be implemented, it would be deadlock-prone in much the manner of suspend(). If the target thread held a lock protecting a critical system resource when it was destroyed, no thread could ever access this resource again. If another thread ever attempted to lock this resource, deadlock would result. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.

Throws NoSuchMethodError.

Throws:: NoSuchMethodError - always

isAlive

public final boolean isAlive()

Tests if this thread is alive. A thread is alive if it has been started and has not yet died.

Returns:: true if this thread is alive; false otherwise.

suspend

@Deprecated
public final void suspend()

Deprecated. This method has been deprecated, as it is inherently deadlock-prone. If the target thread holds a lock on the monitor protecting a critical system resource when it is suspended, no thread can access this resource until the target thread is resumed. If the thread that would resume the target thread attempts to lock this monitor prior to calling resume, deadlock results. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.

Suspends this thread.

First, the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException (in the current thread).

If the thread is alive, it is suspended and makes no further progress unless and until it is resumed.

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

resume

@Deprecated
public final void resume()

Deprecated. This method exists solely for use with suspend(), which has been deprecated because it is deadlock-prone. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.

Resumes a suspended thread.

First, the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException (in the current thread).

If the thread is alive but suspended, it is resumed and is permitted to make progress in its execution.

Throws:: SecurityException - if the current thread cannot modify this thread.
See Also:: checkAccess(), suspend()

setPriority

public final void setPriority(int newPriority)

Changes the priority of this thread.

First the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException.

Otherwise, the priority of this thread is set to the smaller of the specified newPriority and the maximum permitted priority of the thread's thread group.

Parameters:: newPriority - priority to set this thread to
Throws:: IllegalArgumentException - If the priority is not in the range MIN_PRIORITY to MAX_PRIORITY.; SecurityException - if the current thread cannot modify this thread.
See Also:: getPriority(), checkAccess(), getThreadGroup(), MAX_PRIORITY, MIN_PRIORITY, ThreadGroup.getMaxPriority()

getPriority

public final int getPriority()

Returns this thread's priority.

Returns:: this thread's priority.
See Also:: setPriority(int)

setName

public final void setName(String name)

Changes the name of this thread to be equal to the argument name.

First the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException.

Parameters:: name - the new name for this thread.
Throws:: SecurityException - if the current thread cannot modify this thread.
See Also:: getName(), checkAccess()

getName

public final String getName()

Returns this thread's name.

Returns:: this thread's name.
See Also:: setName(String)

getThreadGroup

public final ThreadGroup getThreadGroup()

Returns the thread group to which this thread belongs. This method returns null if this thread has died (been stopped).

Returns:: this thread's thread group.

activeCount

public static int activeCount()

Returns the number of active threads in the current thread's thread group.

Returns:: the number of active threads in the current thread's thread group.

enumerate

public static int enumerate(Thread[] tarray)

Copies into the specified array every active thread in the current thread's thread group and its subgroups. This method simply calls the enumerate method of the current thread's thread group with the array argument.

First, if there is a security manager, that enumerate method calls the security manager's checkAccess method with the thread group as its argument. This may result in throwing a SecurityException.

Parameters:: tarray - an array of Thread objects to copy to
Returns:: the number of threads put into the array
Throws:: SecurityException - if a security manager exists and its checkAccess method doesn't allow the operation.
See Also:: ThreadGroup.enumerate(Thread[]), SecurityManager.checkAccess(ThreadGroup)

countStackFrames

@Deprecated
public int countStackFrames()

Deprecated. The definition of this call depends on suspend(), which is deprecated. Further, the results of this call were never well-defined.

Counts the number of stack frames in this thread. The thread must be suspended.

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

join

public final void join(long millis)
                throws InterruptedException

Waits at most millis milliseconds for this thread to die. A timeout of 0 means to wait forever.

Parameters:: millis - the time to wait in milliseconds.
Throws:: InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

join

public final void join(long millis,
                       int nanos)
                throws InterruptedException

Waits at most millis milliseconds plus nanos nanoseconds for this thread to die.

Parameters:: millis - the time to wait in milliseconds.; nanos - 0-999999 additional nanoseconds to wait.
Throws:: IllegalArgumentException - if the value of millis is negative the value of nanos is not in the range 0-999999.; InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

join

public final void join()
                throws InterruptedException

Waits for this thread to die.

Throws:: InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

dumpStack

public static void dumpStack()

Prints a stack trace of the current thread to the standard error stream. This method is used only for debugging.

See Also:: Throwable.printStackTrace()

setDaemon

public final void setDaemon(boolean on)

Marks this thread as either a daemon thread or a user thread. The Java Virtual Machine exits when the only threads running are all daemon threads.

This method must be called before the thread is started.

This method first calls the checkAccess method of this thread with no arguments. This may result in throwing a SecurityException (in the current thread).

Parameters:: on - if true, marks this thread as a daemon thread.
Throws:: IllegalThreadStateException - if this thread is active.; SecurityException - if the current thread cannot modify this thread.
See Also:: isDaemon(), checkAccess()

isDaemon

public final boolean isDaemon()

Tests if this thread is a daemon thread.

Returns:: true if this thread is a daemon thread; false otherwise.
See Also:: setDaemon(boolean)

checkAccess

public final void checkAccess()

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

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

Throws:: SecurityException - if the current thread is not allowed to access this thread.
See Also:: SecurityManager.checkAccess(Thread)

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 string representation of this thread.

getContextClassLoader

public ClassLoader getContextClassLoader()

Returns the context ClassLoader for this Thread. The context ClassLoader is provided by the creator of the thread for use by code running in this thread when loading classes and resources. If not set, the default is the ClassLoader context of the parent Thread. The context ClassLoader of the primordial thread is typically set to the class loader used to load the application.

First, if there is a security manager, and the caller's class loader is not null and the caller's class loader is not the same as or an ancestor of the context class loader for the thread whose context class loader is being requested, then the security manager's checkPermission method is called with a RuntimePermission("getClassLoader") permission to see if it's ok to get the context ClassLoader..

Returns:: the context ClassLoader for this Thread
Throws:: SecurityException - if a security manager exists and its checkPermission method doesn't allow getting the context ClassLoader.
Since:: 1.2
See Also:: setContextClassLoader(java.lang.ClassLoader), SecurityManager.checkPermission(java.security.Permission), RuntimePermission

setContextClassLoader

public void setContextClassLoader(ClassLoader cl)

Sets the context ClassLoader for this Thread. The context ClassLoader can be set when a thread is created, and allows the creator of the thread to provide the appropriate class loader to code running in the thread when loading classes and resources.

First, if there is a security manager, its checkPermission method is called with a RuntimePermission("setContextClassLoader") permission to see if it's ok to set the context ClassLoader..

Parameters:: cl - the context ClassLoader for this Thread
Throws:: SecurityException - if the current thread cannot set the context ClassLoader.
Since:: 1.2
See Also:: getContextClassLoader(), SecurityManager.checkPermission(java.security.Permission), RuntimePermission

holdsLock

public static boolean holdsLock(Object obj)

Returns true if and only if the current thread holds the monitor lock on the specified object.

This method is designed to allow a program to assert that the current thread already holds a specified lock:

     assert Thread.holdsLock(obj);

Parameters:: obj - the object on which to test lock ownership
Returns:: true if the current thread holds the monitor lock on the specified object.
Throws:: NullPointerException - if obj is null
Since:: 1.4

getStackTrace

public StackTraceElement[] getStackTrace()

Returns an array of stack trace elements representing the stack dump of this thread. This method will return a zero-length array if this thread has not started or has terminated. If the returned array is of non-zero length then the first element of the array represents the top of the stack, which is the most recent method invocation in the sequence. The last element of the array represents the bottom of the stack, which is the least recent method invocation in the sequence.

If there is a security manager, and this thread is not the current thread, then the security manager's checkPermission method is called with a RuntimePermission("getStackTrace") permission to see if it's ok to get the stack trace.

Some virtual machines may, under some circumstances, omit one or more stack frames from the stack trace. In the extreme case, a virtual machine that has no stack trace information concerning this thread is permitted to return a zero-length array from this method.

Returns:: an array of StackTraceElement, each represents one stack frame.
Throws:: SecurityException - if a security manager exists and its checkPermission method doesn't allow getting the stack trace of thread.
Since:: 1.5
See Also:: SecurityManager.checkPermission(java.security.Permission), RuntimePermission, Throwable.getStackTrace()

getAllStackTraces

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

Returns a map of stack traces for all live threads. The map keys are threads and each map value is an array of StackTraceElement that represents the stack dump of the corresponding Thread. The returned stack traces are in the format specified for the getStackTrace method.

The threads may be executing while this method is called. The stack trace of each thread only represents a snapshot and each stack trace may be obtained at different time. A zero-length array will be returned in the map value if the virtual machine has no stack trace information about a thread.

If there is a security manager, then the security manager's checkPermission method is called with a RuntimePermission("getStackTrace") permission as well as RuntimePermission("modifyThreadGroup") permission to see if it is ok to get the stack trace of all threads.

Returns:: a Map from Thread to an array of StackTraceElement that represents the stack trace of the corresponding thread.
Throws:: SecurityException - if a security manager exists and its checkPermission method doesn't allow getting the stack trace of thread.
Since:: 1.5
See Also:: getStackTrace(), SecurityManager.checkPermission(java.security.Permission), RuntimePermission, Throwable.getStackTrace()

getId

public long getId()

Returns the identifier of this Thread. The thread ID is a positive long number generated when this thread was created. The thread ID is unique and remains unchanged during its lifetime. When a thread is terminated, this thread ID may be reused.

Returns:: this thread's ID.
Since:: 1.5

getState

public Thread.State getState()

Returns the state of this thread. This method is designed for use in monitoring of the system state, not for synchronization control.

Returns:: this thread's state.
Since:: 1.5

setDefaultUncaughtExceptionHandler

public static void setDefaultUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)

Set the default handler invoked when a thread abruptly terminates due to an uncaught exception, and no other handler has been defined for that thread.

Uncaught exception handling is controlled first by the thread, then by the thread's ThreadGroup object and finally by the default uncaught exception handler. If the thread does not have an explicit uncaught exception handler set, and the thread's thread group (including parent thread groups) does not specialize its uncaughtException method, then the default handler's uncaughtException method will be invoked.

By setting the default uncaught exception handler, an application can change the way in which uncaught exceptions are handled (such as logging to a specific device, or file) for those threads that would already accept whatever "default" behavior the system provided.

Note that the default uncaught exception handler should not usually defer to the thread's ThreadGroup object, as that could cause infinite recursion.

Parameters:: eh - the object to use as the default uncaught exception handler. If null then there is no default handler.
Throws:: SecurityException - if a security manager is present and it denies RuntimePermission ("setDefaultUncaughtExceptionHandler")
Since:: 1.5
See Also:: setUncaughtExceptionHandler(java.lang.Thread.UncaughtExceptionHandler), getUncaughtExceptionHandler(), ThreadGroup.uncaughtException(java.lang.Thread, java.lang.Throwable)

getDefaultUncaughtExceptionHandler

public static Thread.UncaughtExceptionHandler getDefaultUncaughtExceptionHandler()

Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception. If the returned value is null, there is no default.

Since:: 1.5
See Also:: setDefaultUncaughtExceptionHandler(java.lang.Thread.UncaughtExceptionHandler)

getUncaughtExceptionHandler

public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler()

Returns the handler invoked when this thread abruptly terminates due to an uncaught exception. If this thread has not had an uncaught exception handler explicitly set then this thread's ThreadGroup object is returned, unless this thread has terminated, in which case null is returned.

Since:: 1.5

setUncaughtExceptionHandler

public void setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler eh)

Set the handler invoked when this thread abruptly terminates due to an uncaught exception.

A thread can take full control of how it responds to uncaught exceptions by having its uncaught exception handler explicitly set. If no such handler is set then the thread's ThreadGroup object acts as its handler.

Parameters:: eh - the object to use as this thread's uncaught exception handler. If null then this thread has no explicit handler.
Throws:: SecurityException - if the current thread is not allowed to modify this thread.
Since:: 1.5
See Also:: setDefaultUncaughtExceptionHandler(java.lang.Thread.UncaughtExceptionHandler), ThreadGroup.uncaughtException(java.lang.Thread, java.lang.Throwable)

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java.lang Class Thread

MIN_PRIORITY

NORM_PRIORITY

MAX_PRIORITY

Thread

Thread

Thread

Thread

Thread

Thread

Thread

Thread

currentThread

yield

sleep

sleep

start

run

stop

stop

interrupt

interrupted

isInterrupted

destroy

isAlive

suspend

resume

setPriority

getPriority

setName

getName

getThreadGroup

activeCount

enumerate

countStackFrames

join

join

join

dumpStack

setDaemon

isDaemon

checkAccess

toString

getContextClassLoader

setContextClassLoader

holdsLock

getStackTrace

getAllStackTraces

getId

getState

setDefaultUncaughtExceptionHandler

getDefaultUncaughtExceptionHandler

getUncaughtExceptionHandler

setUncaughtExceptionHandler

java.lang
Class Thread