java Conditions

//Listing 7-2. Achieving Synchronization in Terms of Locks and Conditions
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class A {
public static void main(String[] args) {
Shared s = new Shared();
new Producer(s).start();
new Consumer(s).start();
}
}

class Shared {
private char c;
private volatile boolean available;
private final Lock lock;
private final Condition condition;

Shared() {
available = false;
lock = new ReentrantLock();
condition = lock.newCondition();
}

Lock getLock() {
return lock;
}

char getSharedChar() {
lock.lock();
try {
while (!available)
try {
condition.await();
} catch (InterruptedException ie) {
ie.printStackTrace();
}
available = false;
condition.signal();
} finally {
lock.unlock();
return c;
}
}

void setSharedChar(char c) {
lock.lock();
try {
while (available)
try {
condition.await();
} catch (InterruptedException ie) {
ie.printStackTrace();
}
this.c = c;
available = true;
condition.signal();
} finally {
lock.unlock();
}
}
}

class Producer extends Thread {
private final Lock l;
private final Shared s;

Producer(Shared s) {
this.s = s;
l = s.getLock();
}

@Override
public void run() {
for (char ch = 'A'; ch <= 'Z'; ch++) {
l.lock();
s.setSharedChar(ch);
System.out.println(ch + " produced by producer.");
l.unlock();
}
}
}

class Consumer extends Thread {
private final Lock l;
private final Shared s;

Consumer(Shared s) {
this.s = s;
l = s.getLock();
}

@Override
public void run() {
char ch;
do {
l.lock();
ch = s.getSharedChar();
System.out.println(ch + " consumed by consumer.");
l.unlock();
} while (ch != 'Z');
}
}