import java.util.concurrent.ArrayBlockingQueue;

import java.util.concurrent.BlockingQueue;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.locks.Lock;

import java.util.concurrent.locks.ReentrantLock;

public class PC{

public static void main(String[] args){

final Lock lock = new ReentrantLock();

final BlockingQueue<Character> bq = new ArrayBlockingQueue<Character>(26);

final ExecutorService executor = Executors.newFixedThreadPool(2);

Runnable producer = new Runnable(){

public void run(){

for(char ch='A';ch <= 'Z';ch++){

lock.lock();

try{

while(!bq.offer(ch)){ // full and not insert

lock.unlock();

Thread.sleep(50);

lock.lock(); // reacquire the lock, or reentrant

}

System.out.println(ch + " produced by " + Thread.currentThread());

}catch(InterruptedException ie){

ie.printStackTrace();

}finally{

lock.unlock();

}

}

}

};

executor.execute(producer);

Runnable consumeRunnable = new Runnable(){

public void run(){

char ch = '\0';

do{

try{

lock.lock();

Character c;

while((c = bq.poll()) == null){ // empty, no elements can be polled.

lock.unlock();

Thread.sleep(50);

lock.lock(); // reentrant

}

ch = c.charValue();

System.out.println(ch + " consumed by " + Thread.currentThread());

}catch(InterruptedException ie){

ie.printStackTrace();

}finally{

lock.unlock();

}

}while(ch!='Z');

executor.shutdownNow();

}

};

executor.execute(consumeRunnable);

}

}