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.
Thread(Runnable target, String name)
          Allocates a new Thread object with the given target and name.
Thread(String name)
          Allocates a new Thread object with the given name.
 
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.
 String getName()
          Returns this thread's name.
 int getPriority()
          Returns this thread's priority.
 void interrupt()
          Interrupts this thread.
 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

MAX_PRIORITY

public static final int MAX_PRIORITY
The maximum priority that a thread can have.

MIN_PRIORITY

public static final int MIN_PRIORITY
The minimum priority that a thread can have.

NORM_PRIORITY

public static final int NORM_PRIORITY
The default priority that is assigned to a thread.
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.

Thread

public Thread(Runnable target,
              String name)
Allocates a new Thread object with the given target and name.
Parameters:
target - the object whose run method is called.
name - the name of the new thread.
Since:
JDE 4.0.0

Thread

public Thread(String name)
Allocates a new Thread object with the given name. Threads created this way must have overridden their run() method to actually do anything.
Parameters:
name - the name of the new thread.
Since:
JDE 4.0.0
Method Detail

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.

currentThread

public static Thread currentThread()
Returns a reference to the currently executing thread object.
Returns:
the currently executing thread.

getName

public final String getName()
Returns this thread's name. Note that in CLDC the name of the thread can only be set when creating the thread.
Returns:
this thread's name.
Since:
JDE 4.0.0

getPriority

public final int getPriority()
Returns this thread's priority.
Returns:
this thread's name.
See Also:
setPriority(int), setPriority(int)

interrupt

public void interrupt()
Interrupts this thread. In an implementation conforming to the CLDC Specification, this operation is not required to cancel or clean up any pending I/O operations that the thread may be waiting for.
Since:
JDK 1.0, CLDC 1.1

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.

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.

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.

See Also:
start(), Runnable.run()

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

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()

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.

yield

public static void yield()
Causes the currently executing thread object to temporarily pause and allow other threads to execute.



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