Module java.base
Package java.lang

Class Thread

  • All Implemented Interfaces:
    Runnable
    Direct Known Subclasses:
    ForkJoinWorkerThread
    public classThreadextendsObjectimplementsRunnable
    Athread 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 newThread 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 namedmain of some designated class). The Java Virtual Machine continues to execute threads until either of the following occurs:

    • Theexit method of classRuntime 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 therun method or by throwing an exception that propagates beyond therun method.

    There are two ways to create a new thread of execution. One is to declare a class to be a subclass ofThread. This subclass should override therun method of classThread. 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 theRunnable interface. That class then implements therun method. An instance of the class can then be allocated, passed as an argument when creatingThread, 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.

    Unless otherwise noted, passing anull argument to a constructor or method in this class will cause aNullPointerException to be thrown.

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

    • Nested Class Summary

      Nested Classes 
      Modifier and TypeClassDescription
      static class Thread.State
      A thread state.
      static interface Thread.UncaughtExceptionHandler
      Interface for handlers invoked when aThread abruptly terminates due to an uncaught exception.

    • Field Summary

      Fields 
      Modifier and TypeFieldDescription
      static intMAX_PRIORITY
      The maximum priority that a thread can have.
      static intMIN_PRIORITY
      The minimum priority that a thread can have.
      static intNORM_PRIORITY
      The default priority that is assigned to a thread.

    • Constructor Summary

      Constructors 
      ConstructorDescription
      Thread()
      Allocates a newThread object.
      Thread​(Runnable target)
      Allocates a newThread object.
      Thread​(Runnable target,String name)
      Allocates a newThread object.
      Thread​(String name)
      Allocates a newThread object.
      Thread​(ThreadGroup group,Runnable target)
      Allocates a newThread object.
      Thread​(ThreadGroup group,Runnable target,String name)
      Allocates a newThread object so that it hastarget as its run object, has the specifiedname as its name, and belongs to the thread group referred to bygroup.
      Thread​(ThreadGroup group,Runnable target,String name, long stackSize)
      Allocates a newThread object so that it hastarget as its run object, has the specifiedname as its name, and belongs to the thread group referred to bygroup, and has the specifiedstack size.
      Thread​(ThreadGroup group,Runnable target,String name, long stackSize, boolean inheritThreadLocals)
      Allocates a newThread object so that it hastarget as its run object, has the specifiedname as its name, belongs to the thread group referred to bygroup, has the specifiedstackSize, and inherits initial values forinheritable thread-local variables ifinheritThreadLocals istrue.
      Thread​(ThreadGroup group,String name)
      Allocates a newThread object.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods 
      Modifier and TypeMethodDescription
      static intactiveCount()
      Returns an estimate of the number of active threads in the current thread'sthread group and its subgroups.
      voidcheckAccess()
      Determines if the currently running thread has permission to modify this thread.
      protectedObjectclone()
      Throws CloneNotSupportedException as a Thread can not be meaningfully cloned.
      intcountStackFrames()
      Deprecated, for removal: This API element is subject to removal in a future version.
      The definition of this call depends onsuspend(), which is deprecated.
      staticThreadcurrentThread()
      Returns a reference to the currently executing thread object.
      static voiddumpStack()
      Prints a stack trace of the current thread to the standard error stream.
      static intenumerate​(Thread[] tarray)
      Copies into the specified array every active thread in the current thread's thread group and its subgroups.
      staticMap<Thread,​StackTraceElement[]>getAllStackTraces()
      Returns a map of stack traces for all live threads.
      ClassLoadergetContextClassLoader()
      Returns the contextClassLoader for this thread.
      staticThread.UncaughtExceptionHandlergetDefaultUncaughtExceptionHandler()
      Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception.
      longgetId()
      Returns the identifier of this Thread.
      StringgetName()
      Returns this thread's name.
      intgetPriority()
      Returns this thread's priority.
      StackTraceElement[]getStackTrace()
      Returns an array of stack trace elements representing the stack dump of this thread.
      Thread.StategetState()
      Returns the state of this thread.
      ThreadGroupgetThreadGroup()
      Returns the thread group to which this thread belongs.
      Thread.UncaughtExceptionHandlergetUncaughtExceptionHandler()
      Returns the handler invoked when this thread abruptly terminates due to an uncaught exception.
      static booleanholdsLock​(Object obj)
      Returnstrue if and only if the current thread holds the monitor lock on the specified object.
      voidinterrupt()
      Interrupts this thread.
      static booleaninterrupted()
      Tests whether the current thread has been interrupted.
      booleanisAlive()
      Tests if this thread is alive.
      booleanisDaemon()
      Tests if this thread is a daemon thread.
      booleanisInterrupted()
      Tests whether this thread has been interrupted.
      voidjoin()
      Waits for this thread to die.
      voidjoin​(long millis)
      Waits at mostmillis milliseconds for this thread to die.
      voidjoin​(long millis, int nanos)
      Waits at mostmillis milliseconds plusnanos nanoseconds for this thread to die.
      static voidonSpinWait()
      Indicates that the caller is momentarily unable to progress, until the occurrence of one or more actions on the part of other activities.
      voidresume()
      Deprecated.
      This method exists solely for use withsuspend(), which has been deprecated because it is deadlock-prone.
      voidrun()
      If this thread was constructed using a separateRunnable run object, then thatRunnable object'srun method is called; otherwise, this method does nothing and returns.
      voidsetContextClassLoader​(ClassLoader cl)
      Sets the context ClassLoader for this Thread.
      voidsetDaemon​(boolean on)
      Marks this thread as either adaemon thread or a user thread.
      static voidsetDefaultUncaughtExceptionHandler​(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.
      voidsetName​(String name)
      Changes the name of this thread to be equal to the argumentname.
      voidsetPriority​(int newPriority)
      Changes the priority of this thread.
      voidsetUncaughtExceptionHandler​(Thread.UncaughtExceptionHandler eh)
      Set the handler invoked when this thread abruptly terminates due to an uncaught exception.
      static voidsleep​(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 voidsleep​(long millis, int nanos)
      Causes the currently executing thread to sleep (temporarily 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.
      voidstart()
      Causes this thread to begin execution; the Java Virtual Machine calls therun method of this thread.
      voidstop()
      Deprecated.
      This method is inherently unsafe.
      voidsuspend()
      Deprecated.
      This method has been deprecated, as it is inherently deadlock-prone.
      StringtoString()
      Returns a string representation of this thread, including the thread's name, priority, and thread group.
      static voidyield()
      A hint to the scheduler that the current thread is willing to yield its current use of a processor.

    • 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 newThread object. This constructor has the same effect asThread(null, null, gname), wheregname is a newly generated name. Automatically generated names are of the form"Thread-"+n, wheren is an integer.

      • Thread

        public Thread​(Runnable target)
        Allocates a newThread object. This constructor has the same effect asThread(null, target, gname), wheregname is a newly generated name. Automatically generated names are of the form"Thread-"+n, wheren is an integer.
        Parameters:
        target - the object whoserun method is invoked when this thread is started. Ifnull, this classesrun method does nothing.

      • Thread

        public Thread​(ThreadGroup group,Runnable target)
        Allocates a newThread object. This constructor has the same effect asThread(group, target, gname) ,wheregname is a newly generated name. Automatically generated names are of the form"Thread-"+n, wheren is an integer.
        Parameters:
        group - the thread group. Ifnull and there is a security manager, the group is determined bySecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returnsnull, the group is set to the current thread's thread group.
        target - the object whoserun method is invoked when this thread is started. Ifnull, this thread's run method is invoked.
        Throws:
        SecurityException - if the current thread cannot create a thread in the specified thread group

      • Thread

        public Thread​(String name)
        Allocates a newThread object. This constructor has the same effect asThread(null, null, name).
        Parameters:
        name - the name of the new thread

      • Thread

        public Thread​(ThreadGroup group,String name)
        Allocates a newThread object. This constructor has the same effect asThread(group, null, name).
        Parameters:
        group - the thread group. Ifnull and there is a security manager, the group is determined bySecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returnsnull, the group is set to the current thread's thread group.
        name - the name of the new thread
        Throws:
        SecurityException - if the current thread cannot create a thread in the specified thread group

      • Thread

        public Thread​(Runnable target,String name)
        Allocates a newThread object. This constructor has the same effect asThread(null, target, name).
        Parameters:
        target - the object whoserun method is invoked when this thread is started. Ifnull, this thread's run method is invoked.
        name - the name of the new thread

      • Thread

        public Thread​(ThreadGroup group,Runnable target,String name)
        Allocates a newThread object so that it hastarget as its run object, has the specifiedname as its name, and belongs to the thread group referred to bygroup.

        If there is a security manager, itscheckAccess method is invoked with the ThreadGroup as its argument.

        In addition, itscheckPermission method is invoked with theRuntimePermission("enableContextClassLoaderOverride") permission when invoked directly or indirectly by the constructor of a subclass which overrides thegetContextClassLoader orsetContextClassLoader methods.

        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 methodsetPriority 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 methodsetDaemon may be used to change whether or not a thread is a daemon.

        Parameters:
        group - the thread group. Ifnull and there is a security manager, the group is determined bySecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returnsnull, the group is set to the current thread's thread group.
        target - the object whoserun method is invoked when this thread is started. Ifnull, this thread's run method is invoked.
        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.

      • Thread

        public Thread​(ThreadGroup group,Runnable target,String name,              long stackSize)
        Allocates a newThread object so that it hastarget as its run object, has the specifiedname as its name, and belongs to the thread group referred to bygroup, and has the specifiedstack size.

        This constructor is identical toThread(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 thestackSize parameter, if any, is highly platform dependent.

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

        The virtual machine is free to treat thestackSize 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 thestackSize parameter will cause this constructor to behave exactly like theThread(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 thestackSize parameter.

        Parameters:
        group - the thread group. Ifnull and there is a security manager, the group is determined bySecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returnsnull, the group is set to the current thread's thread group.
        target - the object whoserun method is invoked when this thread is started. Ifnull, this thread's run method is invoked.
        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

      • Thread

        public Thread​(ThreadGroup group,Runnable target,String name,              long stackSize,              boolean inheritThreadLocals)
        Allocates a newThread object so that it hastarget as its run object, has the specifiedname as its name, belongs to the thread group referred to bygroup, has the specifiedstackSize, and inherits initial values forinheritable thread-local variables ifinheritThreadLocals istrue.

        This constructor is identical toThread(ThreadGroup,Runnable,String,long) with the added ability to suppress, or not, the inheriting of initial values for inheritable thread-local variables from the constructing thread. This allows for finer grain control over inheritable thread-locals. Care must be taken when passing a value offalse forinheritThreadLocals, as it may lead to unexpected behavior if the new thread executes code that expects a specific thread-local value to be inherited.

        Specifying a value oftrue for theinheritThreadLocals parameter will cause this constructor to behave exactly like theThread(ThreadGroup, Runnable, String, long) constructor.

        Parameters:
        group - the thread group. Ifnull and there is a security manager, the group is determined bySecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returnsnull, the group is set to the current thread's thread group.
        target - the object whoserun method is invoked when this thread is started. Ifnull, this thread's run method is invoked.
        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
        inheritThreadLocals - iftrue, inherit initial values for inheritable thread-locals from the constructing thread, otherwise no initial values are inherited
        Throws:
        SecurityException - if the current thread cannot create a thread in the specified thread group
        Since:
        9

    • 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()
        A hint to the scheduler that the current thread is willing to yield its current use of a processor. The scheduler is free to ignore this hint.

        Yield is a heuristic attempt to improve relative progression between threads that would otherwise over-utilise a CPU. Its use should be combined with detailed profiling and benchmarking to ensure that it actually has the desired effect.

        It is rarely appropriate to use this method. It may be useful for debugging or testing purposes, where it may help to reproduce bugs due to race conditions. It may also be useful when designing concurrency control constructs such as the ones in thejava.util.concurrent.locks package.

      • sleep

        public static void sleep​(long millis)                  throwsInterruptedException
        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:
        IllegalArgumentException - if the value ofmillis is negative
        InterruptedException - if any thread has interrupted the current thread. Theinterrupted status of the current thread is cleared when this exception is thrown.

      • sleep

        public static void sleep​(long millis,                         int nanos)                  throwsInterruptedException
        Causes the currently executing thread to sleep (temporarily 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 ofmillis is negative, or the value ofnanos is not in the range0-999999
        InterruptedException - if any thread has interrupted the current thread. Theinterrupted status of the current thread is cleared when this exception is thrown.

      • onSpinWait

        public static void onSpinWait()
        Indicates that the caller is momentarily unable to progress, until the occurrence of one or more actions on the part of other activities. By invoking this method within each iteration of a spin-wait loop construct, the calling thread indicates to the runtime that it is busy-waiting. The runtime may take action to improve the performance of invoking spin-wait loop constructions.
        API Note:
        As an example consider a method in a class that spins in a loop until some flag is set outside of that method. A call to theonSpinWait method should be placed inside the spin loop.
             class EventHandler {         volatile boolean eventNotificationNotReceived;         void waitForEventAndHandleIt() {             while ( eventNotificationNotReceived ) {                 java.lang.Thread.onSpinWait();             }             readAndProcessEvent();         }         void readAndProcessEvent() {             // Read event from some source and process it              . . .         }     }

        The code above would remain correct even if theonSpinWait method was not called at all. However on some architectures the Java Virtual Machine may issue the processor instructions to address such code patterns in a more beneficial way.

        Since:
        9

      • start

        public void start()
        Causes this thread to begin execution; the Java Virtual Machine calls therun method of this thread.

        The result is that two threads are running concurrently: the current thread (which returns from the call to thestart method) and the other thread (which executes itsrun 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 separateRunnable run object, then thatRunnable object'srun method is called; otherwise, this method does nothing and returns.

        Subclasses ofThread should override this method.

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

      • stop

        @Deprecated(since="1.2")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 uncheckedThreadDeath 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 ofstop 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), theinterrupt method should be used to interrupt the wait. For more information, seeWhy are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
        Forces the thread to stop executing.

        If there is a security manager installed, itscheckAccess method is called withthis as its argument. This may result in aSecurityException 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'scheckPermission method (with aRuntimePermission("stopThread") argument) is called in addition. Again, this may result in throwing aSecurityException (in the current thread).

        The thread represented by this thread is forced to stop whatever it is doing abnormally and to throw a newly createdThreadDeath 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 catchThreadDeath unless it must do some extraordinary cleanup operation (note that the throwing ofThreadDeath causesfinally clauses oftry statements to be executed before the thread officially dies). If acatch clause catches aThreadDeath 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 ofThreadDeath.

        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)

      • interrupt

        public void interrupt()
        Interrupts this thread.

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

        If this thread is blocked in an invocation of thewait(),wait(long), orwait(long, int) methods of theObject class, or of thejoin(),join(long),join(long, int),sleep(long), orsleep(long, int), methods of this class, then its interrupt status will be cleared and it will receive anInterruptedException.

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

        If this thread is blocked in aSelector 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'swakeup 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. Theinterrupted 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. Theinterrupted 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()

      • 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(since="1.2")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 callingresume, deadlock results. Such deadlocks typically manifest themselves as "frozen" processes. For more information, seeWhy are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
        Suspends this thread.

        First, thecheckAccess method of this thread is called with no arguments. This may result in throwing aSecurityException(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(since="1.2")public final void resume()
        Deprecated.
        This method exists solely for use withsuspend(), which has been deprecated because it is deadlock-prone. For more information, seeWhy are Thread.stop, Thread.suspend and Thread.resume Deprecated?.
        Resumes a suspended thread.

        First, thecheckAccess method of this thread is called with no arguments. This may result in throwing aSecurityException (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 thecheckAccess method of this thread is called with no arguments. This may result in throwing aSecurityException.

        Otherwise, the priority of this thread is set to the smaller of the specifiednewPriority 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 rangeMIN_PRIORITY toMAX_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 argumentname.

        First thecheckAccess method of this thread is called with no arguments. This may result in throwing aSecurityException.

        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 an estimate of the number of active threads in the current thread'sthread group and its subgroups. Recursively iterates over all subgroups in the current thread's thread group.

        The value returned is only an estimate because the number of threads may change dynamically while this method traverses internal data structures, and might be affected by the presence of certain system threads. This method is intended primarily for debugging and monitoring purposes.

        Returns:
        an estimate of the number of active threads in the current thread's thread group and in any other thread group that has the current thread's thread group as an ancestor

      • 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 invokes theThreadGroup.enumerate(Thread[]) method of the current thread's thread group.

        An application might use theactiveCount method to get an estimate of how big the array should be, howeverif 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 the current thread's thread group and its subgroups, the invoker should verify that the returned int value is strictly less than the length oftarray.

        Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.

        Parameters:
        tarray - an array into which to put the list of threads
        Returns:
        the number of threads put into the array
        Throws:
        SecurityException - ifThreadGroup.checkAccess() determines that the current thread cannot access its thread group

      • countStackFrames

        @Deprecated(since="1.2",forRemoval=true)public int countStackFrames()
        Deprecated, for removal: This API element is subject to removal in a future version.
        The definition of this call depends onsuspend(), which is deprecated. Further, the results of this call were never well-defined. This method is subject to removal in a future version of Java SE.
        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.
        See Also:
        StackWalker

      • join

        public final void join​(long millis)                throwsInterruptedException
        Waits at mostmillis milliseconds for this thread to die. A timeout of0 means to wait forever.

        This implementation uses a loop ofthis.wait calls conditioned onthis.isAlive. As a thread terminates thethis.notifyAll method is invoked. It is recommended that applications not usewait,notify, ornotifyAll onThread instances.

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

      • join

        public final void join​(long millis,                       int nanos)                throwsInterruptedException
        Waits at mostmillis milliseconds plusnanos nanoseconds for this thread to die.

        This implementation uses a loop ofthis.wait calls conditioned onthis.isAlive. As a thread terminates thethis.notifyAll method is invoked. It is recommended that applications not usewait,notify, ornotifyAll onThread instances.

        Parameters:
        millis - the time to wait in milliseconds
        nanos -0-999999 additional nanoseconds to wait
        Throws:
        IllegalArgumentException - if the value ofmillis is negative, or the value ofnanos is not in the range0-999999
        InterruptedException - if any thread has interrupted the current thread. Theinterrupted status of the current thread is cleared when this exception is thrown.

      • join

        public final void join()                throwsInterruptedException
        Waits for this thread to die.

        An invocation of this method behaves in exactly the same way as the invocation

        join(0)

        Throws:
        InterruptedException - if any thread has interrupted the current thread. Theinterrupted 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.

      • setDaemon

        public final void setDaemon​(boolean on)
        Marks this thread as either adaemon thread or a user thread. The Java Virtual Machine exits when the only threads running are all daemon threads.

        This method must be invoked before the thread is started.

        Parameters:
        on - iftrue, marks this thread as a daemon thread
        Throws:
        IllegalThreadStateException - if this thread isalive
        SecurityException - ifcheckAccess() determines that the current thread cannot modify this thread

      • 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, itscheckAccess method is called with this thread as its argument. This may result in throwing aSecurityException.

        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 contextClassLoader for this thread. The contextClassLoader is provided by the creator of the thread for use by code running in this thread when loading classes and resources. If notset, the default is theClassLoader context of the parent thread. The contextClassLoader of the primordial thread is typically set to the class loader used to load the application.
        Returns:
        the contextClassLoader for this thread, ornull indicating the system class loader (or, failing that, the bootstrap class loader)
        Throws:
        SecurityException - if a security manager is present, and the caller's class loader is notnull and is not the same as or an ancestor of the context class loader, and the caller does not have theRuntimePermission("getClassLoader")
        Since:
        1.2

      • 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, throughgetContextClassLoader, to code running in the thread when loading classes and resources.

        If a security manager is present, itscheckPermission method is invoked with aRuntimePermission ("setContextClassLoader") permission to see if setting the context ClassLoader is permitted.

        Parameters:
        cl - the context ClassLoader for this Thread, or null indicating the system class loader (or, failing that, the bootstrap class loader)
        Throws:
        SecurityException - if the current thread cannot set the context ClassLoader
        Since:
        1.2

      • holdsLock

        public static boolean holdsLock​(Object obj)
        Returnstrue 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 isnull
        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, has started but has not yet been scheduled to run by the system, 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'scheckPermission method is called with aRuntimePermission("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 ofStackTraceElement, each represents one stack frame.
        Throws:
        SecurityException - if a security manager exists and itscheckPermission 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 ofStackTraceElement that represents the stack dump of the correspondingThread. The returned stack traces are in the format specified for thegetStackTrace 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'scheckPermission method is called with aRuntimePermission("getStackTrace") permission as well asRuntimePermission("modifyThreadGroup") permission to see if it is ok to get the stack trace of all threads.

        Returns:
        aMap fromThread to an array ofStackTraceElement that represents the stack trace of the corresponding thread.
        Throws:
        SecurityException - if a security manager exists and itscheckPermission 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 positivelong 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'sThreadGroup 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 itsuncaughtException method, then the default handler'suncaughtException 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'sThreadGroup object, as that could cause infinite recursion.

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

      • 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'sThreadGroup object is returned, unless this thread has terminated, in which casenull is returned.
        Returns:
        the uncaught exception handler for this thread
        Since:
        1.5