java-design-patterns/registry

title, category, language, tags

title	category	language	tags
Registry	Creational	en	Instantiation

Intent

Stores the objects of a single class and provide a global point of access to them. Similar to Multiton pattern, only difference is that in a registry there is no restriction on the number of objects.

Explanation

In Plain Words

Registry is a well-known object that other objects can use to find common objects and services.

Programmatic Example Below is a Customer Class

public class Customer {

  private final String id;
  private final String name;

  public Customer(String id, String name) {
    this.id = id;
    this.name = name;
  }

  public String getId() {
    return id;
  }

  public String getName() {
    return name;
  }

}

This registry of the Customer objects is CustomerRegistry

public final class CustomerRegistry {

  private static final CustomerRegistry instance = new CustomerRegistry();

  public static CustomerRegistry getInstance() {
    return instance;
  }

  private final Map<String, Customer> customerMap;

  private CustomerRegistry() {
    customerMap = new ConcurrentHashMap<>();
  }

  public Customer addCustomer(Customer customer) {
    return customerMap.put(customer.getId(), customer);
  }

  public Customer getCustomer(String id) {
    return customerMap.get(id);
  }

}

Class diagram

Applicability

Use Registry pattern when

• client wants reference of some object, so client can lookup for that object in the object's registry.

Consequences

Large number of bulky objects added to registry would result in a lot of memory consumption as objects in the registry are not garbage collected.

Credits

• https://www.martinfowler.com/eaaCatalog/registry.html
• https://wiki.c2.com/?RegistryPattern