MULTITHREADING AND PARALLEL PROGRAMMING - Introduction to Java Programming: Comprehensive Version - page 1123

Three concrete blocking queues— ArrayBlockingQueue , LinkedBlockingQueue ,
and PriorityBlockingQueue —are provided in Java, as shown in Figure 30.21. All are
in the java.util.concurrent package. ArrayBlockingQueue implements a block-
ing queue using an array. You have to specify a capacity or an optional fairness to con-
struct an ArrayBlockingQueue . LinkedBlockingQueue implements a blocking queue
using a linked list. You can create an unbounded or bounded LinkedBlockingQueue .
PriorityBlockingQueue is a priority queue. You can create an unbounded or bounded
priority queue.

«interface»
java.util.concurrent.BlockingQueue<E>

ArrayBlockingQueue<E> LinkedBlockingQueue<E> PriorityBlockingQueue<E>

+ArrayBlockingQueue(capacity: int)
+ArrayBlockingQueue(capacity: int,
fair: boolean)

+LinkedBlockingQueue()
+LinkedBlockingQueue(capacity: int)

+PriorityBlockingQueue()
+PriorityBlockingQueue(capacity: int)

F IGURE 30.21

ArrayBlockingQueue , LinkedBlockingQueue , and PriorityBlockingQueue are concrete
blocking queues.

Note
The put method will never block an unbounded LinkedBlockingQueue or
PriorityBlockingQueue .

unbounded queue

Listing 30.8 gives an example of using an ArrayBlockingQueue to simplify the
Consumer/Producer example in Listing 30.10. Line 5 creates an ArrayBlockingQueue to
store integers. The Producer thread puts an integer into the queue (line 22), and the Consumer
thread takes an integer from the queue (line 38).

L ISTING 30.8

ConsumerProducerUsingBlockingQueue.java
1 import java.util.concurrent.*;
2
3 public class ConsumerProducerUsingBlockingQueue {
4

private static ArrayBlockingQueue<Integer> buffer =

5 new ArrayBlockingQueue<>( 2 ); create a buffer

6
7 public static void main(String[] args) {
8 // Create a thread pool with two threads
9 ExecutorService executor = Executors.newFixedThreadPool( 2 );
10 executor.execute( new ProducerTask());
11 executor.execute( new ConsumerTask());
12 executor.shutdown();
13 }
14
15 // A task for adding an int to the buffer
16 private staticclass ProducerTask implements Runnable {
17 public void run() {
18 try {
19 int i = 1 ;
20 while ( true ) {
21 System.out.println( "Producer writes " + i);
22

create two threads

producer task

buffer.put(i++); // Add any value to the buffer, say, 1

put

23 // Put the thread into sleep