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.
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++; } } }
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.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.SecurityException
- if the current thread cannot create a thread in the specified thread group.public Thread(String name)
Thread
object. This constructor has the same effect as Thread(null, null, name)
.name
- the name of the new thread.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.SecurityException
- if the current thread cannot create a thread in the specified thread group.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.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 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. 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.
group
- the thread group.target
- the object whose run
method is called.name
- the name of the new thread.SecurityException
- if the current thread cannot create a thread in the specified thread group.Method Detail |
public static native Thread currentThread()
public static native void yield()
public static native void sleep(long millis)
millis
- the length of time to sleep in milliseconds.InterruptedException
- if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public static void sleep(long millis, int nanos)
millis
- the length of time to sleep in milliseconds.nanos
- 0-999999 additional nanoseconds to sleep.IllegalArgumentException
- if the value of millis is negative or the value of nanos is not in the range 0-999999.InterruptedException
- if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.private void init(ThreadGroup g, Runnable target, String name)
g
- the Thread grouptarget
- the object whose run() method gets calledname
- the name of the new Threadpublic native synchronized 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).
IllegalThreadStateException
- if the thread was already started.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.
private void exit()
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 (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?. If there is a security manager installed, its checkAccess
method is called with this
as its argument. This may result in a SecurityException
being raised (in the current thread).
If this thread is different from the current thread (that is, the current thread is trying to stop a thread other than itself), the security manager's checkPermission
method (with a RuntimePermission("stopThread")
argument) is called in addition. Again, 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
.
SecurityException
- if the current thread cannot modify this thread.public final synchronized void stop(Throwable obj)
If there is a security manager installed, the checkAccess
method of this thread is called, which may result in a SecurityException
being raised (in the current thread).
If this thread is different from the current thread (that is, the current thread is trying to stop a thread other than itself) or obj
is not an instance of ThreadDeath
, the security manager's checkPermission
method (with the RuntimePermission("stopThread")
argument) is called in addition. 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.SecurityException
- if the current thread cannot modify this thread.public void interrupt()
First the checkAccess
method of this thread is called with no arguments. This may result in throwing a SecurityException
.
SecurityException
- if the current thread cannot modify this thread.public static boolean interrupted()
true
if the current thread has been interrupted; false
otherwise.public boolean isInterrupted()
true
if this thread has been interrupted; false
otherwise.private native boolean isInterrupted(boolean ClearInterrupted)
public void destroy()
public final native 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. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?. 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.
SecurityException
- if the current thread cannot modify this thread.public final void resume()
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.
SecurityException
- if the current thread cannot modify this thread.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.
newPriority
- priority to set this thread toIllegalArgumentException
- If the priority is not in the range MIN_PRIORITY
to MAX_PRIORITY
.SecurityException
- if the current thread cannot modify this thread.public final int getPriority()
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.SecurityException
- if the current thread cannot modify this thread.public final String getName()
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. First, if there is a security manager, that enumerate
method calls the security manager's checkAccess
method with the thread group as its argument. This may result in throwing a SecurityException
.
tarray
- an array of Thread objects to copy toSecurityException
- if a security manager exists and its checkAccess
method doesn't allow the operation.public native int countStackFrames()
IllegalThreadStateException
- if this thread is not suspended.public final synchronized void join(long millis)
millis
milliseconds for this thread to die. A timeout of 0
means to wait forever.millis
- the time to wait in milliseconds.InterruptedException
- if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public final synchronized void join(long millis, int nanos)
millis
milliseconds plus nanos
nanoseconds for this thread to die.millis
- the time to wait in milliseconds.nanos
- 0-999999 additional nanoseconds to wait.IllegalArgumentException
- if the value of millis is negative the value of nanos is not in the range 0-999999.InterruptedException
- if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public final void join()
InterruptedException
- if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public static void dumpStack()
public final void setDaemon(boolean on)
This method must be called before the thread is started.
This method first calls the checkAccess
method of this thread with no arguments. This may result in throwing a SecurityException
(in the current thread).
on
- if true
, marks this thread as a daemon thread.IllegalThreadStateException
- if this thread is active.SecurityException
- if the current thread cannot modify this thread.public final boolean isDaemon()
true
if this thread is a daemon thread; false
otherwise.public final 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
.
Note: This method was mistakenly non-final in JDK 1.1. It has been made final in the Java 2 Platform.
SecurityException
- if the current thread is not allowed to access this thread.public String toString()
public ClassLoader getContextClassLoader()
First, if there is a security manager, and the caller's class loader is not null and the caller's class loader is not the same as or an ancestor of the context class loader for the thread whose context class loader is being requested, then the security manager's checkPermission
method is called with a RuntimePermission("getClassLoader")
permission to see if it's ok to get the context ClassLoader..
SecurityException
- if a security manager exists and its checkPermission
method doesn't allow getting the context ClassLoader.public void setContextClassLoader(ClassLoader cl)
First, if there is a security manager, its checkPermission
method is called with a RuntimePermission("setContextClassLoader")
permission to see if it's ok to set the context ClassLoader..
cl
- the context ClassLoader for this ThreadSecurityException
- if the current thread cannot set the context ClassLoader.