import java.util.Random;

/**

* @class UserOrDaemonThread

*

* @brief This class demonstrates the difference between a Java user

* thread and a daemon thread. If its constructor is passed

* "true" it becomes a "daemon" thread, which exits when the

* main thread exits. If it's passed "false" it's a "user"

* thread, which can continue to run even after the main thread

* exits.

*/

public class UserOrDaemonThread extends Thread {

/**

* Keep track of whether this is a "user" or a "daemon" thread.

*/

final private String threadType;

/**

* Number of times to iterate, which is 100 million to ensure the

* program runs for a while.

*/

private final int MAX_ITERATIONS = 100000000;

/**

* Constructor determines what type of thread it being created.

*/

public UserOrDaemonThread(Boolean daemonThread) {

if (daemonThread) {

// Become a daemon thread (setDaemon() obtained from the

// superclass).

setDaemon(true);

threadType = "daemon";

} else

threadType = "user";

}

/**

* Provides a recursive implementation of Euclid's algorithm to

* compute the "greatest common divisor" (GCD), which is the

* largest positive integer that divides two integers without a

* remainder.

*/

private int computeGCD(int number1,

int number2) {

// Basis case.

if (number2 == 0)

return number1;

// Recursive call.

return computeGCD(number2,

number1 % number2);

}

/**

* Hook method that runs for MAX_ITERATIONs.

*/

public void run() {

final String threadString =

" with "

+ threadType

+ " thread id "

+ Thread.currentThread();

System.out.println("Entering run()"

+ threadString);

// Create a new Random number generator. We need to allocate

// a new Random object dynamically since we can't inherit from

// Random since we already inherit from Thread and Java only

// allows single inheritance.

Random random = new Random();

try {

// Iterate for the given # of iterations.

for (int i = 0; i < MAX_ITERATIONS; ++i) {

// Generate two random numbers.

int number1 = random.nextInt();

int number2 = random.nextInt();

// Print results every 10 million iterations.

if ((i % 10000000) == 0)

System.out.println("In run()"

+ threadString

+ " the GCD of "

+ number1

+ " and "

+ number2

+ " is "

+ computeGCD(number1,

number2));

}

}

finally {

System.out.println("Leaving run() "

+ threadString);

}

}

}