Thread Class

Package: java.lang

The Thread class lets you create an object that can be run as a thread in a multithreaded Java application.

Note that an alternative to using the Thread class to crate multithreaded applications is to use the Runnable interface. For more information, see Runnable Interface.

Constructors

Constructor	Description
Thread()	Creates an instance of the Thread class. This constructor is the basic Thread constructor without parameters.
Thread(String name)	Creates a Thread object and assigns the specified name to the thread.
Thread(Runnable target)	Turns any object that implements an API interface called Runnable into a thread. You see how this more-advanced constructor is used later in this part.
Thread(Runnable target, String name)	Creates a thread from any object that implements Runnable and assigns the specified name to the thread.

Methods

Method	Description
static int activeCount()	Returns the number of active threads.
static int enumerate(Thread[] t)	Fills the specified array with a copy of each active thread. The return value is the number of threads added to the array.
String getName()	Returns the name of the thread.
int getPriority()	Returns the thread’s priority.
void interrupt()	Interrupts this thread.
boolean isInterrupted()	Checks whether the thread has been interrupted.
void setPriority(int priority)	Sets the thread’s priority.
void setName(String name)	Sets the thread’s name.
static void Sleep	Causes the currently executing thread (int milliseconds) to sleep for the specified number of milliseconds.
void run()	Is called when the thread is started. Place the code that you want the thread to execute inside this method.
void start()	Starts the thread.
static void yield()	Causes the currently executing thread to yield to other threads that are waiting to execute.

Extending the Thread class

The easiest way to create a thread is to write a class that extends the Thread class. Then all you have to do to start a thread is create an instance of your thread class and call its start method.

A class that extends Thread should include a run method. The run method is automatically called when the thread is started. Note that the run method must either call sleep or yield to give other threads a chance to execute.

Here’s an example of a program that extends the Thread class and counts down the numbers 20 to 1 at one-second intervals:

public class CountDownClock extends Thread

{

public void run()

{

for (int t = 20; t >= 0; t--)

{

System.out.println (t);

try

{

Thread.sleep(1000);

}

catch (InterruptedException e)

{}

}

}

}

Creating and starting a thread

After you define a class that defines a Thread object, you can create and start the thread. Here’s a program that launches the CountDownClock thread shown in the preceding section:

public class CountDownApp

{

public static void main(String[] args)

{

Thread clock = new CountDownClock();

clock.start();

}

}

In this example, a variable of type Thread is declared, and an instance of the CountDownClock is created and assigned to it. This creates a Thread object, but the thread doesn’t begin executing until you call its start method.