Class java.lang.Thread - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.lang.Thread

java.lang.Object
   |
   +----java.lang.Thread

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 performing the stop 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.

See Also:: Runnable, exit, run, stop

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

Thread(): Allocates a new Thread object.
Thread(Runnable): Allocates a new Thread object.
Thread(Runnable, String): Allocates a new Thread object.
Thread(String): Allocates a new Thread object.
Thread(ThreadGroup, Runnable): Allocates a new Thread object.
Thread(ThreadGroup, Runnable, 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(ThreadGroup, String): Allocates a new Thread object.

activeCount(): Returns the current number of active threads in this thread group.
checkAccess(): Determines if the currently running thread has permission to modify this thread.
countStackFrames(): Counts the number of stack frames in this thread.
currentThread(): Returns a reference to the currently executing thread object.
destroy(): Destroys this thread, without any cleanup.
dumpStack(): Prints a stack trace of the current thread.
enumerate(Thread[]): Copies into the specified array every active thread in this thread group and its subgroups.
getName(): Returns this thread's name.
getPriority(): Returns this thread's priority.
getThreadGroup(): Returns this thread's thread group.
interrupt(): Interrupts this thread.
interrupted(): Tests if the current thread has been interrupted.
isAlive(): Tests if this thread is alive.
isDaemon(): Tests if this thread is a daemon thread.
isInterrupted(): Tests if the current thread has been interrupted.
join(): Waits for this thread to die.
join(long): Waits at most millis milliseconds for this thread to die.
join(long, int): Waits at most millis milliseconds plus nanos nanoseconds for this thread to die.
resume(): Resumes a suspended thread.
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.
setDaemon(boolean): Marks this thread as either a daemon thread or a user thread.
setName(String): Changes the name of this thread to be equal to the argument name.
setPriority(int): Changes the priority of this thread.
sleep(long): Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds.
sleep(long, int): Causes the currently executing thread to sleep (cease execution) for the specified number of milliseconds plus the specified number of nanoseconds.
start(): Causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.
stop(): Forces the thread to stop executing.
stop(Throwable): Forces the thread to stop executing.
suspend(): Suspends this thread.
toString(): Returns a string representation of this thread, including the thread's name, priority, and thread group.
yield(): Causes the currently executing thread object to temporarily pause and allow other threads to execute.

MIN_PRIORITY

 public static final int MIN_PRIORITY

The minimum priority that a thread can have.

NORM_PRIORITY

 public static final int NORM_PRIORITY

The default priority that is assigned to a thread.

MAX_PRIORITY

 public static final int MAX_PRIORITY

The maximum priority that a thread can have.

Thread

 public Thread()

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

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

     import java.lang.*; 
     class plain01 implements Runnable {
         String name; 
         plain01() {
             name = null;
         }
         plain01(String s) {
             name = s;
         }
         public void run() {
             if (name == null)
                 System.out.println("A new thread created");
             else
                 System.out.println("A new thread with name " + name +
                                    " created");
         }
     }
     class threadtest01 {
         public static void main(String args[] ) {
             int failed = 0 ;
             Thread t1 = new Thread();  
             if (t1 != null)
                 System.out.println("new Thread() succeed");
             else {
                 System.out.println("new Thread() failed"); 
                 failed++; 
             }
         }
     }

See Also:: Thread

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

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

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

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

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

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 not null, the checkAccess method of that thread group is called with no arguments; this may result in throwing a SecurityException; if group is null, the new process belongs to the same group as the thread that is creating the new thread.

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.
See Also:: run, run, setDaemon, setPriority, checkAccess

currentThread

 public static native Thread currentThread()

Returns a reference to the currently executing thread object.

Returns:: the currently executing thread.

yield

 public static native void yield()

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

sleep

 public static native void sleep(long millis) throws InterruptedException

Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds. The thread does not lose ownership of any monitors.

Parameters:: millis - the length of time to sleep in milliseconds.
Throws: InterruptedException: if another thread has interrupted this thread.
See Also:: notify

sleep

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

Causes the currently executing thread to sleep (cease execution) for the specified number of milliseconds plus the specified number of nanoseconds. The thread does not lose ownership of any monitors.

Parameters:: millis - the length of time to sleep in milliseconds.; nanos - 0-999999 additional nanoseconds to sleep.
Throws: IllegalArgumentException: if the value of millis is negative or the value of nanos is not in the range 0-999999.
Throws: InterruptedException: if another thread has interrupted this thread.
See Also:: notify

start

 public native synchronized void start()

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

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

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

run

 public void run()

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

Subclasses of Thread should override this method.

See Also:: start, stop, Thread, run

stop

 public final void stop()

Forces the thread to stop executing.

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

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

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

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

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

Note: the use of this method is unsafe as it can result in the corruption of invariants. 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 behaviour. Many uses of stop should be replaced by code that simply modifies some volatile 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, the interrupt method should be used to interrupt the wait.

Throws: SecurityException: if the current thread cannot modify this thread.
See Also:: checkAccess, run, start, ThreadDeath, uncaughtException

stop

 public final synchronized void stop(Throwable o)

Forces the thread to stop executing.

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

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

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

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

Parameters:: obj - the Throwable object to be thrown.
Throws: SecurityException: if the current thread cannot modify this thread.
See Also:: checkAccess, run, start, stop

interrupt

 public void interrupt()

Interrupts this thread.

interrupted

 public static boolean interrupted()

Tests if the current thread has been interrupted. Note that interrupted is a static method, while isInterrupted is called on the current Thread instance.

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

isInterrupted

 public boolean isInterrupted()

Tests if the current thread has been interrupted. Note that isInterrupted is called on the current Thread instance; by contrast, interrupted is a static method.

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

destroy

 public void destroy()

Destroys this thread, without any cleanup. Any monitors it has locked remain locked. (This method is not implemented in Java 1.0.2.)

isAlive

 public final native 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

 public final void suspend()

Suspends this thread.

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

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

Throws: SecurityException: if the current thread cannot modify this thread.
See Also:: checkAccess, isAlive

resume

 public final void resume()

Resumes a suspended thread.

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

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

Throws: SecurityException: if the current thread cannot modify this thread.
See Also:: checkAccess, isAlive

setPriority

 public final void setPriority(int newPriority)

Changes the priority of this thread.

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

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

Throws: IllegalArgumentException: If the priority is not in the range MIN_PRIORITY to MAX_PRIORITY.
Throws: SecurityException: if the current thread cannot modify this thread.
See Also:: checkAccess, getPriority, getThreadGroup, MAX_PRIORITY, MIN_PRIORITY, getMaxPriority

getPriority

 public final int getPriority()

Returns this thread's priority.

Returns:: this thread's name.
See Also:: setPriority

setName

 public final void setName(String name)

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

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

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

getName

 public final String getName()

Returns this thread's name.

Returns:: this thread's name.
See Also:: setName

getThreadGroup

 public final ThreadGroup getThreadGroup()

Returns this thread's thread group.

Returns:: this thread's thread group.

activeCount

 public static int activeCount()

Returns the current number of active threads in this thread group.

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

enumerate

 public static int enumerate(Thread tarray[])

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

Returns:: the number of threads put into the array.
See Also:: enumerate

countStackFrames

 public native int countStackFrames()

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

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

join

 public final synchronized void join(long millis) throws InterruptedException

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

Parameters:: millis - the time to wait in milliseconds.
Throws: InterruptedException: if another thread has interrupted the current thread.

join

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

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

Parameters:: millis - the time to wait in milliseconds.; nanos - 0-999999 additional nanoseconds to wait.
Throws: IllegalArgumentException: if the value of millis is negative the value of nanos is not in the range 0-999999.
Throws: InterruptedException: if another thread has interrupted the current thread.

join

 public final void join() throws InterruptedException

Waits for this thread to die.

Throws: InterruptedException: if another thread has interrupted the current thread.

dumpStack

 public static void dumpStack()

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

See Also:: printStackTrace

setDaemon

 public final void setDaemon(boolean on)

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

This method must be called before the thread is started.

Parameters:: on - if true, marks this thread as a daemon thread.
Throws: IllegalThreadStateException: if this thread is active.
See Also:: isDaemon

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

checkAccess

 public void checkAccess()

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

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

Throws: SecurityException: if the current thread is not allowed to access this thread.
See Also:: checkAccess

toString

 public String toString()

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

Returns:: a string representation of this thread.
Overrides:: toString in class Object

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