java.lang
Class Thread

java.lang.Object
  java.lang.Thread

All Implemented Interfaces:

Runnable

Direct Known Subclasses:

Accessory

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:

• 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 {
         int minPrime;
         PrimeThread(int 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 {
         int minPrime;
         PrimeRun(int 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, run()

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.

Method Summary

static Thread	currentThread() Returns a reference to the currently executing thread object.
protected void	finalize() finalize method
String	getName() get the name of the thread
int	getPriority() Returns this thread's priority.
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	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	setDaemon(boolean on) Marks this thread as either a daemon thread or a user thread.
void	setName(String name) set the name of the thread
void	setPriority(int newPriority) Changes the priority of this thread.
void	start() Causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.
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, getClass, notifyAll, toString, 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.

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

public Thread(Runnable target)

Allocates a new Thread object.

Parameters:

target - the object whose run method is called.

Method Detail

currentThread

public static Thread currentThread()

Returns a reference to the currently executing thread object.

Returns:

the currently executing thread.

yield

public static void yield()

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

start

public 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).

See Also:

run()

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. java.lang.Runnable, java.lang.String)

Specified by:

run in interface Runnable

See Also:

Runnable.run()

interrupt

public void interrupt()

Interrupts this thread.

If this thread is blocked in an invocation of the wait() method of the Object class, or of the sleep(int) method of the ThreadExt class, then its interrupt status will be cleared and it will receive an InterruptedException.

If none of the previous conditions hold then this thread's interrupt status will be set.

interrupted

public static boolean interrupted()

Tests whether the current thread has been interrupted. The interrupted status of the thread is cleared by this method. In other words, if this method were to be called twice in succession, the second call would return false (unless the current thread were interrupted again, after the first call had cleared its interrupted status and before the second call had examined it).

Returns:

true if the current thread has been interrupted; false otherwise.

See Also:

isInterrupted()

isInterrupted

public boolean isInterrupted()

Tests whether this thread has been interrupted. The interrupted status of the thread is unaffected by this method.

Returns:

true if this thread has been interrupted; false otherwise.

See Also:

interrupted()

setPriority

public void setPriority(int newPriority)

Changes the priority of this thread.

Parameters:

newPriority - priority to set this thread to

Throws:

IllegalArgumentException - If the priority is not in the range MIN_PRIORITY to MAX_PRIORITY.

See Also:

getPriority(), getPriority(), MAX_PRIORITY, MIN_PRIORITY

getPriority

public final int getPriority()

Returns this thread's priority.

Returns:

this thread's name.

See Also:

setPriority(int), setPriority(int)

join

public final void join()
                throws InterruptedException

Waits for this thread to die.

Throws:

InterruptedException - if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

setDaemon

public 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.

Parameters:

on - if true, marks this thread as a daemon thread.

See Also:

isDaemon()

isDaemon

public boolean isDaemon()

Tests if this thread is a daemon thread.

Returns:

true if this thread is a daemon thread; false otherwise.

See Also:

setDaemon(boolean)

isAlive

public 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.

setName

public void setName(String name)

set the name of the thread

Parameters:

name -

getName

public String getName()

get the name of the thread

Returns:

finalize

protected void finalize()

finalize method