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 single sequential flow of control within a process. This simply means that while executing within a program, each thread has a beginning, a sequence, a point of execution occurring at any time during runtime of the thread and of course, an ending. Thread objects are the basis for multi-threaded programming. Multi-threaded programming allows a single program to conduct concurrently running threads that perform different tasks.

To create a new thread of execution, declare a new class which is a subclass of Thread and then override the run() method with code that you want executed in this Thread. An instance of the Thread subclass should be created next with a call to the start() method following the instance. The start() method will create the thread and execute the run() method. For example:

	class PrimeThread extends Thread {
	    public void run() {
		// compute primes...
	    }
	}
 

To start this thread you need to do the following:

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

Another way to create a thread is by using the Runnable interface. This way any object that implements the Runnable interface can be run in a thread. For example:

	class Primes implements Runnable {
	    public void run() {
		// compute primes...
	    }
	}
 

To start this thread you need to do the following:

	Primes p = new Primes();
	new Thread(p).start();
	...
 

The virtual machine runs until all Threads that are not daemon Threads have died. A Thread dies when its run() method returns, or when the stop() method is called.

When a new Thread is created, it inherits the priority and the daemon flag from its parent (i.e.: the Thread that created it).

See Also:

Runnable

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()
Constructs a new Thread.

Thread(Runnable target)
Constructs a new Thread which applies the run() method of the specified target.

Thread(Runnable target, String name)
Constructs a new Thread with the specified name and applies the run() method of the specified target.

Thread(String name)
Constructs a new Thread with the specified name.

Thread(ThreadGroup group, Runnable target)
Constructs a new Thread in the specified Thread group that applies the run() method of the specified target.

Thread(ThreadGroup group, Runnable target, String name)
Constructs a new Thread in the specified Thread group with the specified name and applies the run() method of the specified target.

Thread(ThreadGroup group, String name)
Constructs a new Thread in the specified Thread group with the specified name.

Method Summary

static int	activeCount() Returns the current number of active Threads in this Thread group.
void	checkAccess() Checks whether the current Thread is allowed to modify this Thread.
int	countStackFrames() Returns the number of stack frames in this Thread.
static Thread	currentThread() Returns a reference to the currently executing Thread object.
void	destroy() Destroy a thread, without any cleanup, i.e.
static void	dumpStack() A debugging procedure to print a stack trace for the current Thread.
static int	enumerate(Thread[] tarray) Copies, into the specified array, references to every active Thread in this Thread's group.
String	getName() Gets and returns this Thread's name.
int	getPriority() Gets and returns the Thread's priority.
ThreadGroup	getThreadGroup() Gets and returns this Thread group.
void	interrupt() Send an interrupt to a thread.
static boolean	interrupted() Ask if you have been interrupted.
boolean	isAlive() Returns a boolean indicating if the Thread is active.
boolean	isDaemon() Returns the daemon flag of the Thread.
boolean	isInterrupted() Ask if another thread has been interrupted.
void	join() Waits forever for this Thread to die.
void	join(long millis) Waits for this Thread to die.
void	join(long millis, int nanos) Waits for the Thread to die, with more precise time.
void	resume() Resumes this Thread execution.
void	run() The actual body of this Thread.
void	setDaemon(boolean on) Marks this Thread as a daemon Thread or a user Thread.
void	setName(String name) Sets the Thread's name.
void	setPriority(int newPriority) Sets the Thread's priority.
static void	sleep(long millis) Causes the currently executing Thread to sleep for the specified number of milliseconds.
static void	sleep(long millis, int nanos) Sleep, in milliseconds and additional nanosecond.
void	start() Starts this Thread.
void	stop() Stops a Thread by tossing an object.
void	stop(Throwable o) Stops a Thread by tossing an object.
void	suspend() Suspends this Thread's execution.
String	toString() Returns a String representation of the Thread, including the thread's name, priority and thread group.
static void	yield() Causes the currently executing Thread object to yield.

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. The most minimal priority is equal to 1.

See Also:

Constant Field Values

NORM_PRIORITY

public static final int NORM_PRIORITY

The default priority that is assigned to a Thread. The default priority is equal to 5.

See Also:

Constant Field Values

MAX_PRIORITY

public static final int MAX_PRIORITY

The maximum priority that a Thread can have. The maximal priority value a Thread can have is 10.

See Also:

Constant Field Values

Constructor Detail

Thread

public Thread()

Constructs a new Thread. Threads created this way must have overridden their run() method to actually do anything. An example illustrating this method being used is shown.

 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

public Thread(Runnable target)

Constructs a new Thread which applies the run() method of the specified target.

Parameters:

target - the object whose run() method is called

Thread

public Thread(ThreadGroup group,
              Runnable target)

Constructs a new Thread in the specified Thread group that applies the run() method of the specified target.

Parameters:

group - the Thread group

target - the object whose run() method is called

Thread

public Thread(String name)

Constructs a new Thread with the specified name.

Parameters:

name - the name of the new Thread

Thread

public Thread(ThreadGroup group,
              String name)

Constructs a new Thread in the specified Thread group with the specified name.

Parameters:

group - the Thread group

name - the name of the new Thread

Thread

public Thread(Runnable target,
              String name)

Constructs a new Thread with the specified name and applies the run() method of the specified target.

Parameters:

target - the object whose run() method is called

name - the name of the new Thread

Thread

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

Constructs a new Thread in the specified Thread group with the specified name and applies the run() method of the specified target.

Parameters:

group - the Thread group

target - the object whose run() method is called

name - the name of the new Thread

Method Detail

currentThread

public static Thread currentThread()

Returns a reference to the currently executing Thread object.

yield

public static void yield()

Causes the currently executing Thread object to yield. If there are other runnable Threads they will be scheduled next.

sleep

public static void sleep(long millis)
                  throws InterruptedException

Causes the currently executing Thread to sleep for the specified number of milliseconds.

Parameters:

millis - the length of time to sleep in milliseconds

Throws:

InterruptedException - Another thread has interrupted this thread.

sleep

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

Sleep, in milliseconds and additional nanosecond.

Parameters:

millis - the length of time to sleep in milliseconds

nanos - 0-999999 additional nanoseconds to sleep

Throws:

InterruptedException - Another thread has interrupted this thread.

start

public void start()

Starts this Thread. This will cause the run() method to be called. This method will return immediately.

Throws:

IllegalThreadStateException - If the thread was already started.

See Also:

run(), stop()

run

public void run()

The actual body of this Thread. This method is called after the Thread is started. You must either override this method by subclassing class Thread, or you must create the Thread with a Runnable target.

Specified by:

run in interface Runnable

See Also:

start(), stop()

stop

public final void stop()

Stops a Thread by tossing an object. By default this routine tosses a new instance of ThreadDeath to the target Thread. ThreadDeath is not actually a subclass of Exception, but is a subclass of Object. Users should not normally try to catch ThreadDeath unless they must do some extraordinary cleanup operation. If ThreadDeath is caught it is important to rethrow the object so that the thread will actually die. The top-level error handler will not print out a message if ThreadDeath falls through.

See Also:

start(), run()

stop

public final void stop(Throwable o)

Stops a Thread by tossing an object. Normally, users should just call the stop() method without any argument. However, in some exceptional circumstances used by the stop() method to kill a Thread, another object is tossed. ThreadDeath, is not actually a subclass of Exception, but is a subclass of Throwable

Parameters:

o - the Throwable object to be thrown

See Also:

start(), run()

interrupt

public void interrupt()

Send an interrupt to a thread.

interrupted

public static boolean interrupted()

Ask if you have been interrupted.

isInterrupted

public boolean isInterrupted()

Ask if another thread has been interrupted.

destroy

public void destroy()

Destroy a thread, without any cleanup, i.e. just toss its state; any monitors it has locked remain locked. A last resort.

isAlive

public final boolean isAlive()

Returns a boolean indicating if the Thread is active. Having an active Thread means that the Thread has been started and has not been stopped.

suspend

public final void suspend()

Suspends this Thread's execution.

resume

public final void resume()

Resumes this Thread execution. This method is only valid after suspend() has been invoked.

setPriority

public final void setPriority(int newPriority)

Sets the Thread's priority.

Throws:

IllegalArgumentException - If the priority is not within the range MIN_PRIORITY, MAX_PRIORITY.

See Also:

MIN_PRIORITY, MAX_PRIORITY, getPriority()

getPriority

public final int getPriority()

Gets and returns the Thread's priority.

See Also:

setPriority(int)

setName

public final void setName(String name)

Sets the Thread's name.

Parameters:

name - the new name of the Thread

See Also:

getName()

getName

public final String getName()

Gets and returns this Thread's name.

See Also:

setName(java.lang.String)

getThreadGroup

public final ThreadGroup getThreadGroup()

Gets and returns this Thread group.

activeCount

public static int activeCount()

Returns the current number of active Threads in this Thread group.

enumerate

public static int enumerate(Thread[] tarray)

Copies, into the specified array, references to every active Thread in this Thread's group.

Returns:

the number of Threads put into the array.

countStackFrames

public int countStackFrames()

Returns the number of stack frames in this Thread. The Thread must be suspended when this method is called.

Throws:

IllegalThreadStateException - If the Thread is not suspended.

join

public final void join(long millis)
                throws InterruptedException

Waits for this Thread to die. A timeout in milliseconds can be specified. A timeout of 0 milliseconds means to wait forever.

Parameters:

millis - the time to wait in milliseconds

Throws:

InterruptedException - Another thread has interrupted this thread.

join

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

Waits for the Thread to die, with more precise time.

Throws:

InterruptedException - Another thread has interrupted this thread.

join

public final void join()
                throws InterruptedException

Waits forever for this Thread to die.

Throws:

InterruptedException - Another thread has interrupted this thread.

dumpStack

public static void dumpStack()

A debugging procedure to print a stack trace for the current Thread.

See Also:

Throwable.printStackTrace()

setDaemon

public final void setDaemon(boolean on)

Marks this Thread as a daemon Thread or a user Thread. When there are only daemon Threads left running in the system, Java exits.

Parameters:

on - determines whether the Thread will be a daemon Thread

Throws:

IllegalThreadStateException - If the Thread is active.

See Also:

isDaemon()

isDaemon

public final boolean isDaemon()

Returns the daemon flag of the Thread.

See Also:

setDaemon(boolean)

checkAccess

public void checkAccess()

Checks whether the current Thread is allowed to modify this Thread.

Throws:

SecurityException - If the current Thread is not allowed to access this Thread group.

toString

public String toString()

Returns a String representation of the Thread, including the thread's name, priority and thread group.

Overrides:

toString in class Object