java.lang
Class Thread

java.lang.Object   
  java.lang.Thread

All Implemented Interfaces:

Runnable

public class Thread
extends Object   
implements Runnable   

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

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

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

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

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

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

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

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

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

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

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

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

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

Since:

JDK1.0

See Also:

Runnable , Runtime.exit(int) , run() , stop()

Nested Class Summary

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

Field Summary

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

Constructor Summary

Thread ()
Allocates a new Thread object.

Thread (Runnable target)
Allocates a new Thread object.

Thread (Runnable target, String name)
Allocates a new Thread object.

Thread (String name)
Allocates a new Thread object.

Thread (ThreadGroup group, Runnable target)
Allocates a new Thread object.

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

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

Thread (ThreadGroup group, String name)
Allocates a new Thread object.

Method Summary

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

Methods inherited from class java.lang.Object

clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait

Field Detail

MIN_PRIORITY

public static final int MIN_PRIORITY

The minimum priority that a thread can have.

See Also:

Constant Field Values

NORM_PRIORITY

public static final int NORM_PRIORITY

The default priority that is assigned to a thread.

See Also:

Constant Field Values

MAX_PRIORITY

public static final int MAX_PRIORITY

The maximum priority that a thread can have.

See Also:

Constant Field Values

Constructor Detail

Thread

public Thread()

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

See Also:

Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

public Thread(Runnable    target)

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

Parameters:

target - the object whose run method is called.

See Also:

Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

public Thread(ThreadGroup    group,
              Runnable    target)

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

Parameters:

group - the thread group.

target - the object whose run method is called.

Throws:

SecurityException - if the current thread cannot create a thread in the specified thread group.

See Also:

Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

public Thread(String    name)

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

Parameters:

name - the name of the new thread.

See Also:

Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

public Thread(ThreadGroup    group,
              String    name)

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

Parameters:

group - the thread group.

name - the name of the new thread.

Throws:

SecurityException - if the current thread cannot create a thread in the specified thread group.

See Also:

Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

public Thread(Runnable    target,
              String    name)

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

Parameters:

target - the object whose run method is called.

name - the name of the new thread.

See Also:

Thread(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String)

Thread

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

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

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

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

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

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

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

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

Parameters:

group - the thread group.

target - the object whose run method is called.

name - the name of the new thread.

Throws:

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

See Also:

Runnable.run() , run() , setDaemon(boolean) , setPriority(int) , ThreadGroup.checkAccess() , SecurityManager.checkAccess(java.lang.Thread)

Thread

public Thread(ThreadGroup    group,
              Runnable    target,
              String