Added in API level 1

Thread

open class Thread : Runnable

kotlin.Any
↳	java.lang.Thread

Known Direct Subclasses ForkJoinWorkerThread, HandlerThread ForkJoinWorkerThread A thread managed by a ForkJoinPool, which executes ForkJoinTasks. HandlerThread A Thread that has a Looper.

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.

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

Summary

Nested classes
	State A thread state.
abstract	UncaughtExceptionHandler Interface for handlers invoked when a Thread abruptly terminates due to an uncaught exception.

Constants
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.

Public constructors
Thread() Allocates a new Thread object.
Thread(target: Runnable?) Allocates a new Thread object.
Thread(group: ThreadGroup?, target: Runnable?) Allocates a new Thread object.
Thread(name: String) Allocates a new Thread object.
Thread(group: ThreadGroup?, name: String) Allocates a new Thread object.
Thread(target: Runnable?, name: String) Allocates a new Thread object.
Thread(group: ThreadGroup?, target: Runnable?, name: String) 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(group: ThreadGroup?, target: Runnable?, name: String, stackSize: Long) 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, and has the specified stack size.
Thread(group: ThreadGroup?, target: Runnable?, name: String, stackSize: Long, inheritThreadLocals: Boolean) 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, has the specified stackSize, and inherits initial values for inheritable thread-local variables if inheritThreadLocals is true.

Public methods
open static Int	activeCount() Returns an estimate of the number of active threads in the current thread's thread group and its subgroups.
Unit	checkAccess() Determines if the currently running thread has permission to modify this thread.
open Int	countStackFrames() Counts the number of stack frames in this thread.
open static Thread	currentThread() Returns a reference to the currently executing thread object.
open Unit	destroy() Throws UnsupportedOperationException.
open static Unit	dumpStack() Prints a stack trace of the current thread to the standard error stream.
open static Int	enumerate(tarray: Array<Thread!>!) Copies into the specified array every active thread in the current thread's thread group and its subgroups.
open static MutableMap<Thread!, Array<StackTraceElement!>!>	getAllStackTraces() Returns a map of stack traces for all live threads.
open ClassLoader?	getContextClassLoader() Returns the context ClassLoader for this thread.
open static Thread.UncaughtExceptionHandler?	getDefaultUncaughtExceptionHandler() Returns the default handler invoked when a thread abruptly terminates due to an uncaught exception.
open Long	getId() Returns the identifier of this Thread.
String	getName() Returns this thread's name.
Int	getPriority() Returns this thread's priority.
open Array<StackTraceElement!>	getStackTrace() Returns an array of stack trace elements representing the stack dump of this thread.
open Thread.State	getState() Returns the state of this thread.
ThreadGroup?	getThreadGroup() Returns the thread group to which this thread belongs.
open Thread.UncaughtExceptionHandler?	getUncaughtExceptionHandler() Returns the handler invoked when this thread abruptly terminates due to an uncaught exception.
open static Boolean	holdsLock(obj: Any) Returns true if and only if the current thread holds the monitor lock on the specified object.
open Unit	interrupt() Interrupts this thread.
open 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.
open Boolean	isInterrupted() Tests whether this thread has been interrupted.
Unit	join(millis: Long) Waits at most millis milliseconds for this thread to die.
Unit	join(millis: Long, nanos: Int) Waits at most millis milliseconds plus nanos nanoseconds for this thread to die.
Unit	join() Waits for this thread to die.
open static Unit	onSpinWait() Indicates that the caller is momentarily unable to progress, until the occurrence of one or more actions on the part of other activities.
Unit	resume() Throws UnsupportedOperationException.
open Unit	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.
open Unit	setContextClassLoader(cl: ClassLoader?) Sets the context ClassLoader for this Thread.
Unit	setDaemon(on: Boolean) Marks this thread as either a daemon thread or a user thread.
open static Unit	setDefaultUncaughtExceptionHandler(eh: Thread.UncaughtExceptionHandler?) 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.
Unit	setName(name: String) Changes the name of this thread to be equal to the argument name.
Unit	setPriority(newPriority: Int) Changes the priority of this thread.
open Unit	setUncaughtExceptionHandler(eh: Thread.UncaughtExceptionHandler?) Set the handler invoked when this thread abruptly terminates due to an uncaught exception.
open static Unit	sleep(millis: Long) 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.
open static Unit	sleep(millis: Long, nanos: Int) 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.
open Unit	start() Causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.
Unit	stop() Throws UnsupportedOperationException.
Unit	stop(obj: Throwable?) Throws UnsupportedOperationException.
Unit	suspend() Throws UnsupportedOperationException.
open String	toString() Returns a string representation of this thread, including the thread's name, priority, and thread group.
open static Unit	yield() A hint to the scheduler that the current thread is willing to yield its current use of a processor.

Protected methods
open Any	clone() Throws CloneNotSupportedException as a Thread can not be meaningfully cloned.

Constants

MAX_PRIORITY

Added in API level 1

static val MAX_PRIORITY: Int

The maximum priority that a thread can have.

Value: 10

MIN_PRIORITY

Added in API level 1

static val MIN_PRIORITY: Int

The minimum priority that a thread can have.

Value: 1

NORM_PRIORITY

Added in API level 1

static val NORM_PRIORITY: Int

The default priority that is assigned to a thread.

Value: 5

Public constructors

Thread

Added in API level 1

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.

Thread

Added in API level 1

Thread(target: Runnable?)

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	Runnable?: the object whose run method is invoked when this thread is started. If null, this classes run method does nothing.

Thread

Added in API level 1

Thread(
    group: ThreadGroup?, 
    target: Runnable?)

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	ThreadGroup?: the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
target	Runnable?: the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.

Exceptions
java.lang.SecurityException	if the current thread cannot create a thread in the specified thread group

Thread

Added in API level 1

Thread(name: String)

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

Parameters
name	String: the name of the new thread

Thread

Added in API level 1

Thread(
    group: ThreadGroup?, 
    name: String)

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

Parameters
group	ThreadGroup?: the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
name	String: the name of the new thread

Exceptions
java.lang.SecurityException	if the current thread cannot create a thread in the specified thread group

Thread

Added in API level 1

Thread(
    target: Runnable?, 
    name: String)

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

Parameters
target	Runnable?: the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
name	String: the name of the new thread

Thread

Added in API level 1

Thread(
    group: ThreadGroup?, 
    target: Runnable?, 
    name: String)

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

In addition, its checkPermission method is invoked with the RuntimePermission("enableContextClassLoaderOverride") permission when invoked directly or indirectly by the constructor of a subclass which overrides the getContextClassLoader or setContextClassLoader 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 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	ThreadGroup?: the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
target	Runnable?: the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
name	String: the name of the new thread

Exceptions
java.lang.SecurityException	if the current thread cannot create a thread in the specified thread group or cannot override the context class loader methods.

Thread

Added in API level 1

Thread(
    group: ThreadGroup?, 
    target: Runnable?, 
    name: String, 
    stackSize: Long)

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, and has the specified stack size.

This constructor is identical to Thread(java.lang.ThreadGroup,java.lang.Runnable,java.lang.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	ThreadGroup?: the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
target	Runnable?: the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
name	String: the name of the new thread
stackSize	Long: the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored.

Exceptions
java.lang.SecurityException	if the current thread cannot create a thread in the specified thread group

Thread

Added in API level 33

Thread(
    group: ThreadGroup?, 
    target: Runnable?, 
    name: String, 
    stackSize: Long, 
    inheritThreadLocals: Boolean)

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, has the specified stackSize, and inherits initial values for inheritable thread-local variables if inheritThreadLocals is true.

This constructor is identical to Thread(java.lang.ThreadGroup,java.lang.Runnable,java.lang.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 of false for inheritThreadLocals, 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 of true for the inheritThreadLocals parameter will cause this constructor to behave exactly like the Thread(ThreadGroup, Runnable, String, long) constructor.

Parameters
group	ThreadGroup?: the thread group. If null and there is a security manager, the group is determined by SecurityManager.getThreadGroup(). If there is not a security manager or SecurityManager.getThreadGroup() returns null, the group is set to the current thread's thread group.
target	Runnable?: the object whose run method is invoked when this thread is started. If null, this thread's run method is invoked.
name	String: the name of the new thread
stackSize	Long: the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored
inheritThreadLocals	Boolean: if true, inherit initial values for inheritable thread-locals from the constructing thread, otherwise no initial values are inherited

Exceptions
java.lang.SecurityException	if the current thread cannot create a thread in the specified thread group

Public methods

activeCount

Added in API level 1

open static fun activeCount(): Int

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

Return
Int	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

checkAccess

Added in API level 1

fun checkAccess(): Unit

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.

Exceptions
java.lang.SecurityException	if the current thread is not allowed to access this thread.

See Also

• java.lang.SecurityManager#checkAccess(Thread)

countStackFrames

Added in API level 1
Deprecated in API level 15

open fun countStackFrames(): Int

Deprecated: The definition of this call depends on suspend, 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.

Return
Int	the number of stack frames in this thread.

Exceptions
java.lang.IllegalThreadStateException	if this thread is not suspended.

currentThread

Added in API level 1

open static fun currentThread(): Thread

Returns a reference to the currently executing thread object.

Return
Thread	the currently executing thread.

destroy

Added in API level 1
Deprecated in API level 15

open fun destroy(): Unit

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 UnsupportedOperationException.

Exceptions
java.lang.UnsupportedOperationException	always

dumpStack

Added in API level 1

open static fun dumpStack(): Unit

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

See Also

• java.lang.Throwable#printStackTrace()

enumerate

Added in API level 1

open static fun enumerate(tarray: Array<Thread!>!): Int

Copies into the specified array every active thread in the current thread's thread group and its subgroups. This method simply invokes the java.lang.ThreadGroup#enumerate(Thread[]) method of the current thread's thread group.

An application might use the activeCount method to get an estimate of how big the array should be, however if the array is too short to hold all the threads, the extra threads are silently ignored. If it is critical to obtain every active thread in the current thread's thread group and its subgroups, the invoker should verify that the returned int value is strictly less than the length of tarray.

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	Array<Thread!>!: an array into which to put the list of threads

Return
Int	the number of threads put into the array

Exceptions
java.lang.SecurityException	if java.lang.ThreadGroup#checkAccess determines that the current thread cannot access its thread group

getAllStackTraces

Added in API level 1

open static fun getAllStackTraces(): MutableMap<Thread!, Array<StackTraceElement!>!>

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.

Return
MutableMap<Thread!, Array<StackTraceElement!>!>	a Map from Thread to an array of StackTraceElement that represents the stack trace of the corresponding thread.

See Also

• #getStackTrace
• java.lang.RuntimePermission
• java.lang.Throwable#getStackTrace

getContextClassLoader

Added in API level 1

open fun getContextClassLoader(): ClassLoader?

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.

Return
ClassLoader?	the context ClassLoader for this thread, or null indicating the system class loader (or, failing that, the bootstrap class loader)

Exceptions
java.lang.SecurityException	if the current thread cannot get the context ClassLoader

getDefaultUncaughtExceptionHandler

Added in API level 1

open static fun getDefaultUncaughtExceptionHandler(): Thread.UncaughtExceptionHandler?

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.

Return
Thread.UncaughtExceptionHandler?	the default uncaught exception handler for all threads

See Also

• #setDefaultUncaughtExceptionHandler

getId

Added in API level 1

open fun getId(): Long

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.

Return
Long	this thread's ID.

getName

Added in API level 1

fun getName(): String

Returns this thread's name.

Return
String	this thread's name.

See Also

• #setName(String)

getPriority

Added in API level 1

fun getPriority(): Int

Returns this thread's priority.

Return
Int	this thread's priority.

See Also

• #setPriority

getStackTrace

Added in API level 1

open fun getStackTrace(): Array<StackTraceElement!>

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'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.

Return
Array<StackTraceElement!>	an array of StackTraceElement, each represents one stack frame.

Exceptions
java.lang.SecurityException	if a security manager exists and its checkPermission method doesn't allow getting the stack trace of thread.

See Also

• java.lang.RuntimePermission
• java.lang.Throwable#getStackTrace

getState

Added in API level 1

open fun getState(): Thread.State

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

Return
Thread.State	this thread's state.

getThreadGroup

Added in API level 1

fun getThreadGroup(): ThreadGroup?

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

Return
ThreadGroup?	this thread's thread group.

getUncaughtExceptionHandler

Added in API level 1

open fun getUncaughtExceptionHandler(): Thread.UncaughtExceptionHandler?

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.

Return
Thread.UncaughtExceptionHandler?	the uncaught exception handler for this thread

holdsLock

Added in API level 1

open static fun holdsLock(obj: Any): Boolean

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	Any: the object on which to test lock ownership

Return
Boolean	true if the current thread holds the monitor lock on the specified object.

Exceptions
java.lang.NullPointerException	if obj is null

interrupt

Added in API level 1

open fun interrupt(): Unit

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 then the channel will be closed, the thread's interrupt status will be set, and the thread will receive a .

If this thread is blocked in a java.nio.channels.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.

Exceptions
java.lang.SecurityException	if the current thread cannot modify this thread

interrupted

Added in API level 1

open static fun interrupted(): Boolean

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.

Return
Boolean	true if the current thread has been interrupted; false otherwise.

See Also

• #isInterrupted()

isAlive

Added in API level 1

fun isAlive(): Boolean

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

Return
Boolean	true if this thread is alive; false otherwise.

isDaemon

Added in API level 1

fun isDaemon(): Boolean

Tests if this thread is a daemon thread.

Return
Boolean	true if this thread is a daemon thread; false otherwise.

See Also

• #setDaemon(boolean)

isInterrupted

Added in API level 1

open fun isInterrupted(): Boolean

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.

Return
Boolean	true if this thread has been interrupted; false otherwise.

See Also

• #interrupted()

join

Added in API level 1

fun join(millis: Long): Unit

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

This implementation uses a loop of this.wait calls conditioned on this.isAlive. As a thread terminates the this.notifyAll method is invoked. It is recommended that applications not use wait, notify, or notifyAll on Thread instances.

Parameters
millis	Long: the time to wait in milliseconds

Exceptions
java.lang.IllegalArgumentException	if the value of millis is negative
java.lang.InterruptedException	if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

join

Added in API level 1

fun join(
    millis: Long, 
    nanos: Int
): Unit

Waits at most millis milliseconds plus nanos nanoseconds for this thread to die. If both arguments are 0, it means to wait forever.

This implementation uses a loop of this.wait calls conditioned on this.isAlive. As a thread terminates the this.notifyAll method is invoked. It is recommended that applications not use wait, notify, or notifyAll on Thread instances.

Parameters
millis	Long: the time to wait in milliseconds
nanos	Int: 0-999999 additional nanoseconds to wait

Exceptions
java.lang.IllegalArgumentException	if the value of millis is negative, or the value of nanos is not in the range 0-999999
java.lang.InterruptedException	if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

join

Added in API level 1

fun join(): Unit

Waits for this thread to die.

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

join(0)

Exceptions
java.lang.InterruptedException	if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

onSpinWait

Added in API level 33

open static fun onSpinWait(): Unit

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.

resume

Added in API level 1
Deprecated in API level 15

fun resume(): Unit

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?.

Throws UnsupportedOperationException.

Exceptions
java.lang.UnsupportedOperationException	always

run

Added in API level 1

open fun run(): Unit

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.

See Also

• #start()
• #stop()
• #Thread(ThreadGroup, Runnable, String)

setContextClassLoader

Added in API level 1

open fun setContextClassLoader(cl: ClassLoader?): Unit

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, through getContextClassLoader, to code running in the thread when loading classes and resources.

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

Parameters
cl	ClassLoader?: the context ClassLoader for this Thread, or null indicating the system class loader (or, failing that, the bootstrap class loader)

Exceptions
java.lang.SecurityException	if the current thread cannot set the context ClassLoader

setDaemon

Added in API level 1

fun setDaemon(on: Boolean): Unit

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 invoked before the thread is started.

Parameters
on	Boolean: if true, marks this thread as a daemon thread

Exceptions
java.lang.IllegalThreadStateException	if this thread is alive
java.lang.SecurityException	if checkAccess determines that the current thread cannot modify this thread

setDefaultUncaughtExceptionHandler

Added in API level 1

open static fun setDefaultUncaughtExceptionHandler(eh: Thread.UncaughtExceptionHandler?): Unit

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	Thread.UncaughtExceptionHandler?: the object to use as the default uncaught exception handler. If null then there is no default handler.

See Also

• #setUncaughtExceptionHandler
• #getUncaughtExceptionHandler
• java.lang.ThreadGroup#uncaughtException

setName

Added in API level 1

fun setName(name: String): Unit

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	String: the new name for this thread.

Exceptions
java.lang.SecurityException	if the current thread cannot modify this thread.

See Also

• #getName
• #checkAccess()

setPriority

Added in API level 1

fun setPriority(newPriority: Int): Unit

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	Int: priority to set this thread to

Exceptions
java.lang.IllegalArgumentException	If the priority is not in the range MIN_PRIORITY to MAX_PRIORITY.
java.lang.SecurityException	if the current thread cannot modify this thread.

See Also

• #getPriority
• #checkAccess()
• #getThreadGroup()
• #MAX_PRIORITY
• #MIN_PRIORITY
• java.lang.ThreadGroup#getMaxPriority()

setUncaughtExceptionHandler

Added in API level 1

open fun setUncaughtExceptionHandler(eh: Thread.UncaughtExceptionHandler?): Unit

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	Thread.UncaughtExceptionHandler?: the object to use as this thread's uncaught exception handler. If null then this thread has no explicit handler.

Exceptions
java.lang.SecurityException	if the current thread is not allowed to modify this thread.

See Also

• #setDefaultUncaughtExceptionHandler
• java.lang.ThreadGroup#uncaughtException

sleep

Added in API level 1

open static fun sleep(millis: Long): Unit

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	Long: the length of time to sleep in milliseconds

Exceptions
java.lang.IllegalArgumentException	if the value of millis is negative
java.lang.InterruptedException	if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

sleep

Added in API level 1

open static fun sleep(
    millis: Long, 
    nanos: Int
): Unit

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	Long: the length of time to sleep in milliseconds
nanos	Int: 0-999999 additional nanoseconds to sleep

Exceptions
java.lang.IllegalArgumentException	if the value of millis is negative, or the value of nanos is not in the range 0-999999
java.lang.InterruptedException	if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

start

Added in API level 1

open fun start(): Unit

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.

Exceptions
java.lang.IllegalThreadStateException	if the thread was already started.

See Also

• #run()
• #stop()

stop

Added in API level 1
Deprecated in API level 15

fun stop(): Unit

Deprecated: This method was originally designed to force a thread to stop and throw a ThreadDeath as an exception. It was 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?.

Throws UnsupportedOperationException.

stop

Added in API level 1
Deprecated in API level 15

fun stop(obj: Throwable?): Unit

Deprecated: This method was originally designed to force a thread to stop and throw a given Throwable as an exception. It was inherently unsafe (see stop() for details), and furthermore could be used to generate exceptions that the target thread was not prepared to handle. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?.

Throws UnsupportedOperationException.

Parameters
obj	Throwable?: ignored

suspend

Added in API level 1
Deprecated in API level 15

fun suspend(): Unit

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?.

Throws UnsupportedOperationException.

Exceptions
java.lang.UnsupportedOperationException	always

toString

Added in API level 1

open fun toString(): String

Returns a string representation of this thread, including the thread's name, priority, and thread group.

Return
String	a string representation of this thread.

yield

Added in API level 1

open static fun yield(): Unit

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 the java.util.concurrent.locks package.

Protected methods

clone

Added in API level 1

protected open fun clone(): Any

Throws CloneNotSupportedException as a Thread can not be meaningfully cloned. Construct a new Thread instead.

Return
Any	a clone of this instance.

Exceptions
java.lang.CloneNotSupportedException	always