20.20

java.lang.Thread

THE PACKAGE JAVA.LANG

When a Java Virtual Machine starts up, there is usually a single non daemon

thread, which typically begins by invoking the method

main

 of some designated

class. The Java Virtual Machine continues to execute threads according to the

thread execution model until all threads that are not daemon threads have stopped.

There are two ways to create a new thread of execution. One is to declare

some 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 created and

started. For example, consider code for a thread whose job is to compute primes

larger than a stated value:

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 is to declare some class to implement the

Runnable

 interface, which also requires that the class implement the

run

 method.

An instance of the class can then be created, used to create a

Thread

, and started.

The same example in this other style looks like this:

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:

590