• Implementation 1:
  
  

  public class Customer {
      private final String id;
  
      private final Mediator mediator;
  
      public Customer(final String id, final Mediator mediator) {
          this.id = id;
          this.mediator = mediator;
  
          mediator.add(this);
      }
  
      public String getId() {
          return id;
      }
  
      public void lookup(final String productId) {
          mediator.lookup(this, productId);
      }
  
      public void notify(final Supplier supplier, final String productId) {
          System.out.println("[Customer: " + id + "] Supplier '" + supplier.getId() + "' has the product: " + productId);
      }
  }

  
  
• Implementation 1:
  
  

  public class Supplier {
      private final String id;
  
      private final Mediator mediator;
  
      public Supplier(final String id, final Mediator mediator) {
          this.id = id;
          this.mediator = mediator;
  
          mediator.add(this);
      }
  
      public String getId() {
          return id;
      }
  
      public void notify(final String productId) {
          mediator.notify(this, productId);
      }
  
      public void lookup(final Customer customer, final String productId) {
          System.out.println("[Supplier: " + id + "] Customer '" + customer.getId() + "' looking for product: " + productId);
      }
  }

  
  

public interface Mediator {
    void add(final Customer customer);

    void add(final Supplier supplier);

    void lookup(final Customer customer, final String productId);

    void notify(final Supplier supplier, final String productId);
}

public class MediatorImpl implements Mediator {
    List<Customer> customers = new ArrayList<Customer>();
    List<Supplier> suppliers = new ArrayList<Supplier>();

    public void add(final Customer customer) {
        customers.add(customer);
    }

    public void add(final Supplier supplier) {
        suppliers.add(supplier);
    }

    public void lookup(final Customer customer, final String productId) {
        for (Supplier supplier : suppliers) {
            supplier.lookup(customer, productId);
        }
    }

    public void notify(final Supplier supplier, final String productId) {
        for (Customer customer : customers) {
            customer.notify(supplier, productId);
        }
    }
}

public class MediatorPatternTest {
    public static void main(String[] args) {
        final Mediator mediator = new MediatorImpl();

        final Customer customer = new Customer("customer1", mediator);

        final Supplier supplier = new Supplier("supplier1", mediator);

        final String productId = "1";

        customer.lookup(productId);
        supplier.notify(productId);
    }
}