Design Patterns - Mediator

Design Patterns | Mediator

References
Example

References
- Definition: (source: http://en.wikipedia.org/wiki/Mediator_pattern)
  
  The Mediator pattern defines an object that encapsulates how a set of objects interact.
- Class diagram: (source: http://en.wikipedia.org/wiki/Mediator_pattern)

Example

The Subject (1):

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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);
    }
}

The Subject (2):

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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);
    }
}

The Mediator:

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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);
}

The Concrete Mediator:

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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);
        }
    }
}

A simple class to test the Mediator design pattern:

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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);
    }
}