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');
    }
}