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Java Platform 1.2 Beta 4 |
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SUMMARY: INNER | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |
java.lang.Object | +--java.lang.Thread
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:
exit
method of class Runtime
has been
called and the security manager has permitted the exit operation
to take place.
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.
Runnable
,
Runtime.exit(int)
,
run()
,
stop()
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,
String name)
Allocates a new Thread object. |
|
Thread(Runnable target)
Allocates a new Thread object. |
|
Thread(String name)
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)
Allocates a new Thread object. |
|
Thread(ThreadGroup group,
String name)
Allocates a new Thread object. |
Method Summary | |
static int | activeCount()
Returns the current number of active threads in this 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()
Destroys this thread, without any cleanup. |
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 this this thread's thread group and its subgroups. |
ClassLoader | getContextClassLoader()
Returns the context ClassLoader for this Thread. |
String | getName()
Returns this thread's name. |
int | getPriority()
Returns this thread's priority. |
ThreadGroup | getThreadGroup()
Returns this thread's thread group. |
void | interrupt()
Interrupts this thread. |
static boolean | interrupted()
Tests if 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 if this thread has been interrupted. |
void | join()
Waits 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 | join(long millis)
Waits at most millis milliseconds for this thread to
die. |
void | 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. |
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. |
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. |
static void | sleep(long millis)
Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds. |
void | start()
Causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.
|
void | stop()
Deprecated. |
void | stop(Throwable obj)
Deprecated. |
void | suspend()
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 |
public static final int MIN_PRIORITY
public static final int NORM_PRIORITY
public static final int MAX_PRIORITY
Constructor Detail |
public Thread()
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++; } } }
Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(Runnable target)
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.
target
- the object whose run
method is called.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(ThreadGroup group, Runnable target)
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.
group
- the thread group.
target
- the object whose run
method is called.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(String name)
Thread
object. This constructor has
the same effect as Thread(null, null, name)
.
name
- the name of the new thread.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(ThreadGroup group, String name)
Thread
object. This constructor has
the same effect as Thread(group, null, name)
group
- the thread group.
name
- the name of the new thread.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(Runnable target, String name)
Thread
object. This constructor has
the same effect as Thread(null, target, name)
.
target
- the object whose run
method is called.
name
- the name of the new thread.Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
public Thread(ThreadGroup group, Runnable target, String name)
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.
group
- the thread group.
target
- the object whose run
method is called.
name
- the name of the new thread.Runnable.run()
,
run()
,
setDaemon(boolean)
,
setPriority(int)
,
ThreadGroup.checkAccess()
Method Detail |
public static Thread currentThread()
public static void yield()
public static void sleep(long millis) throws InterruptedException
millis
- the length of time to sleep in milliseconds.Object.notify()
public static void sleep(long millis, int nanos) throws InterruptedException
millis
- the length of time to sleep in milliseconds.
nanos
- 0-999999 additional nanoseconds to sleep.Object.notify()
public void start()
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).
run()
,
stop()
public void run()
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.
start()
,
stop()
,
Thread(java.lang.ThreadGroup,
java.lang.Runnable, java.lang.String)
,
Runnable.run()
public final void stop()
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 (e.g., for input), the interrupt
method should be used to interrupt the wait.
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
.
interrupt()
,
checkAccess()
,
run()
,
start()
,
ThreadDeath
,
ThreadGroup.uncaughtException(java.lang.Thread,
java.lang.Throwable)
public final void stop(Throwable obj)
stop()
method
(with no arguments) 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).
If there is a security manager installed, and this thread is equal
to the current thread (i.e., the current thread is trying to stop
itself), and the Throwable
object obj
is
an instance of ThreadDeath
(i.e., the stop
method without any arguments was called), this method first calls the
security manager's checkAccess
method with this thread
as its argument, which invokes the security manager's
checkPermission
method with the
RuntimePermission("modifyThread")
permission to ensure the current thread has permission to modify
(i.e., stop) itself.
This may result in throwing a
SecurityException
(in the current thread).
However, if there is a security manager installed, and this thread
is different from the current thread (i.e., the current thread is
trying to stop a thread other than itself) or the
Throwable
object obj
is not an instance
of ThreadDeath
, this method first calls the security
manager's checkPermission
method with the
RuntimePermission("stopThread")
permission to ensure the current thread has permission to stop this
thread.
Again, this may result in throwing a
SecurityException
(in the current thread).
If the argument obj
is null, a
NullPointerException
is thrown (in the current thread).
The thread represented by this thread is forced to 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.
obj
- the Throwable object to be thrown.interrupt()
,
checkAccess()
,
run()
,
start()
,
stop()
public void interrupt()
public static boolean interrupted()
interrupted
is a static method, while
isInterrupted
is called on this
Thread
instance.true
if the current thread has been interrupted;
false
otherwise.isInterrupted()
public boolean isInterrupted()
isInterrupted
is called on this Thread
instance; by
contrast, interrupted
is a static method.true
if this thread has been interrupted;
false
otherwise.interrupted()
public void destroy()
public final boolean isAlive()
true
if this thread is alive;
false
otherwise.public final void suspend()
resume
, deadlock results. Such
deadlocks typically manifest themselves as "frozen" processes.
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.
public final void resume()
suspend
, which is deadlock-prone. See
suspend
for details.
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.
suspend()
public final void setPriority(int newPriority)
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.
MIN_PRIORITY
to
MAX_PRIORITY
.checkAccess()
,
getPriority()
,
getThreadGroup()
,
MAX_PRIORITY
,
MIN_PRIORITY
,
ThreadGroup.getMaxPriority()
public final int getPriority()
setPriority(int)
public final void setName(String name)
name
.
First the checkAccess
method of this thread is called
with no arguments. This may result in throwing a
SecurityException
.
name
- the new name for this thread.checkAccess()
,
getName()
public final String getName()
setName(java.lang.String)
public final ThreadGroup getThreadGroup()
public static int activeCount()
public static int enumerate(Thread[] tarray)
enumerate
method of this thread's thread
group with the array argument.ThreadGroup.enumerate(java.lang.Thread[])
public int countStackFrames()
suspend()
,
which is deprecated. Further, the results of this call
were never well-defined.public final void join(long millis) throws InterruptedException
millis
milliseconds for this thread to
die. A timeout of 0
means to wait forever.
millis
- the time to wait in milliseconds.public final void join(long millis, int nanos) throws InterruptedException
millis
milliseconds plus
nanos
nanoseconds for this thread to die.
millis
- the time to wait in milliseconds.
nanos
- 0-999999 additional nanoseconds to wait.public final void join() throws InterruptedException
public static void dumpStack()
Throwable.printStackTrace()
public final void setDaemon(boolean on)
This method must be called before the thread is started.
on
- if true
, marks this thread as a
daemon thread.isDaemon()
public final boolean isDaemon()
true
if this thread is a daemon thread;
false
otherwise.setDaemon(boolean)
public void checkAccess()
If there is a security manager, its checkAccess
method
is called with this thread as its argument. This may result in
throwing a SecurityException
.
SecurityManager.checkAccess(java.lang.Thread)
public String toString()
public ClassLoader getContextClassLoader()
public void setContextClassLoader(ClassLoader cl)
cl
- the context ClassLoader for this Thread
|
Java Platform 1.2 Beta 4 |
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PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||||
SUMMARY: INNER | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |