// Purpose. Mediator design pattern

// 1. Create an "intermediary" that decouples "senders" from "receivers"
// 2. Producers are coupled only to the Mediator
// 3. Consumers are coupled only to the Mediator
// 4. The Mediator arbitrates the storing and retrieving of messages

class Mediator { // 1. The "intermediary"
private boolean slotFull = false; // 4. The Mediator arbitrates
private int number;
public synchronized void storeMessage( int num ) {
while (slotFull == true) // no room for another message
try { wait(); } catch (InterruptedException e ) { }
slotFull = true;
number = num;
notifyAll();
}
public synchronized int retrieveMessage() {
while (slotFull == false) // no message to retrieve
try { wait(); } catch (InterruptedException e ) { }
slotFull = false;
notifyAll();
return number;
} }

class Producer extends Thread {
private Mediator med; // 2. Producers are coupled only to
private int id; // the Mediator
private static int num = 1;
public Producer( Mediator m ) { med = m; id = num++; }
public void run() {
int num;
while (true) {
med.storeMessage( num = (int)(Math.random()*100) );
System.out.print( "p" + id + "-" + num + " " );
} } }

class Consumer extends Thread {
private Mediator med; // 3. Consumers are coupled only to
private int id; // the Mediator
private static int num = 1;
public Consumer( Mediator m ) { med = m; id = num++; }
public void run() {
while (true) {
System.out.print( "c" + id + "-" + med.retrieveMessage() + " " );
} } }

class MediatorDemo {
public static void main( String[] args ) {
Mediator mb = new Mediator();
new Producer( mb ).start();
new Producer( mb ).start();
new Consumer( mb ).start();
new Consumer( mb ).start();
new Consumer( mb ).start();
new Consumer( mb ).start();
} }

// p1-87 c1-87 p2-37 c3-37 p1-28 c2-28 p2-58 c1-58 p1-18 c4-18
// p2-42 c3-42 p1-3 c2-3 p2-11 c3-11 p1-72 c2-72 p2-75 c3-75
// p1-93 c4-93 p2-52 c1-52 p1-21 c3-21 p2-80 c4-80 p1-96 c2-96