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 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.

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();
 

Since:

JDK1.0

See Also:

Runnable, Runtime.exit(int), 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 with a specific target object whose run method is called.

Method Summary

static int	activeCount() Returns the current number of active threads in the VM.
static Thread	currentThread() Returns a reference to the currently executing thread object.
int	getPriority() Returns this thread's priority.
boolean	isAlive() Tests if this thread is alive.
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	setPriority(int newPriority) Changes the priority of this thread.
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.
String	toString() Returns a string representation of this thread, including a unique number that identifies the thread and the thread's priority.
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

equals, 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.

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.

See Also:

Runnable

Thread

public Thread(Runnable target)

Allocates a new Thread object with a specific target object whose run method is called.

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.

sleep

public static 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 the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

See Also:

Object.notify()

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).

Throws:

IllegalThreadStateException - if the thread was already started.

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.

Specified by:

run in interface Runnable

See Also:

start(), Runnable.run()

isAlive

public final 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.

setPriority

public final 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)

activeCount

public static int activeCount()

Returns the current number of active threads in the VM.

Returns:

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

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.

toString

public String toString()

Returns a string representation of this thread, including a unique number that identifies the thread and the thread's priority.

Overrides:

toString in class Object

Returns:

a string representation of this thread.