add first impl

role-object/README.md

@@ -14,9 +14,22 @@ tags:
 Post pattern, Extension Object pattern
 
 ## Intent
+Adapt an object to different client’s needs through transparently attached role objects, each one representing a role
+the object has to play in that client’s context. The object manages its role set dynamically. By representing roles as
+individual objects, different contexts are kept separate and system configuration is simplified.
 
 ## Applicability
-
-## Real world examples
+Use the Role Object pattern, if:
+- you want to handle a key abstraction in different contexts and you do not want to put the resulting contextspecific interfaces into the same class interface.
+Words: 4895 Page 3 of 11
+- you want to handle the available roles dynamically so that they can be attached and removed on demand, that is
+at runtime, rather than fixing them statically at compile-time.
+- you want to treat the extensions transparently and need to preserve the logical object identity of the resulting
+object conglomerate.
+- you want to keep role/client pairs independent from each other so that changes to a role do not affect clients
+that are not interested in that role.
 
 ## Credits
+- [Hillside - Role object pattern](https://hillside.net/plop/plop97/Proceedings/riehle.pdf)
+- [Role object](http://wiki.c2.com/?RoleObject)
+- [Fowler - Dealing with roles](https://martinfowler.com/apsupp/roles.pdf)

role-object/src/main/java/com/iluwatar/roleobject/ApplicationRoleObject.java

@@ -1,7 +1,60 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2019 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
 package com.iluwatar.roleobject;
 
+/**
+ * The Role Object pattern suggests to model context-specific views
+ * of an object as separate role objects which are
+ * dynamically attached to and removed from the core object.
+ * We call the resulting composite object structure,
+ * consisting of the core and its role objects, a subject.
+ * A subject often plays several roles and the same role is likely to
+ * be played by different subjects.
+ * As an example consider two different customers playing the role of borrower and
+ * investor, respectively. Both roles could as well be played by a single Customer object.
+ * The common superclass for customer-specific roles is provided by CustomerRole,
+ * which also supports the Customer interface.
+ * The CustomerRole class is abstract and not meant to be instantiated.
+ * Concrete subclasses of CustomerRole, for example Borrower or Investor,
+ * define and implement the interface for specific roles. It is only
+ * these subclasses which are instantiated at runtime.
+ * The Borrower class defines the context-specific view of
+ * Customer objects as needed by the loan department.
+ * It defines additional operations to manage the customer’s
+ * credits and securities. Similarly, the Investor class adds operations specific
+ * to the investment department’s view of customers.
+ * A client like the loan application may either work with objects of the CustomerCore class, using the interface class
+ * Customer, or with objects of concrete CustomerRole subclasses. Suppose the loan application knows a particular
+ * Customer instance through its Customer interface. The loan application may want to check whether the Customer
+ * object plays the role of Borrower.
+ * To this end it calls hasRole() with a suitable role specification. For the purpose of
+ * our example, let’s assume we can name roles with a simple string.
+ * If the Customer object can play the role named
+ * “Borrower,” the loan application will ask it to return a reference to the corresponding object.
+ * The loan application may now use this reference to call Borrower-specific operations.
+ *
+ */
 public class ApplicationRoleObject {
     public static void main(String[] args) {
-        System.out.println("Role-object");
     }
 }

role-object/src/main/java/com/iluwatar/roleobject/BorrowerRole.java

@@ -0,0 +1,4 @@
+package com.iluwatar.roleobject;
+
+public class BorrowerRole extends CustomerRole{
+}

role-object/src/main/java/com/iluwatar/roleobject/Customer.java

@@ -0,0 +1,12 @@
+package com.iluwatar.roleobject;
+
+import java.util.Optional;
+
+public abstract class Customer {
+
+    public abstract boolean addRole(Role role);
+    public abstract boolean hasRole(Role role);
+    public abstract boolean remRole(Role role);
+    public abstract <T extends Customer> Optional<T> getRole(Role role,Class<T> expectedRole);
+
+}

role-object/src/main/java/com/iluwatar/roleobject/CustomerCore.java

@@ -0,0 +1,35 @@
+package com.iluwatar.roleobject;
+
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+
+public class CustomerCore extends Customer {
+
+    private Map<Role, CustomerRole> roles;
+
+
+    @Override
+    public boolean addRole(Role role) {
+        return role.instance()
+                .map(rI -> roles.put(role, rI))
+                .isPresent();
+    }
+
+    @Override
+    public boolean hasRole(Role role) {
+        return roles.containsKey(role);
+    }
+
+    @Override
+    public boolean remRole(Role role) {
+        return Objects.nonNull(roles.remove(role));
+    }
+
+    @Override
+    public <T extends Customer> Optional<T> getRole(Role role, Class<T> expectedRole) {
+        return Optional.ofNullable(roles.get(role))
+                .filter(expectedRole::isInstance)
+                .map(expectedRole::cast);
+    }
+}

role-object/src/main/java/com/iluwatar/roleobject/CustomerRole.java

@@ -0,0 +1,25 @@
+package com.iluwatar.roleobject;
+
+import java.util.Optional;
+
+public class CustomerRole extends Customer{
+    @Override
+    public boolean addRole(Role role) {
+        return false;
+    }
+
+    @Override
+    public boolean hasRole(Role role) {
+        return false;
+    }
+
+    @Override
+    public boolean remRole(Role role) {
+        return false;
+    }
+
+    @Override
+    public <T extends Customer> Optional<T> getRole(Role role, Class<T> expectedRole) {
+        return Optional.empty();
+    }
+}

role-object/src/main/java/com/iluwatar/roleobject/InvestorRole.java

@@ -0,0 +1,4 @@
+package com.iluwatar.roleobject;
+
+public class InvestorRole extends CustomerRole{
+}

role-object/src/main/java/com/iluwatar/roleobject/Role.java

@@ -0,0 +1,30 @@
+package com.iluwatar.roleobject;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import sun.rmi.runtime.Log;
+
+import java.util.Optional;
+
+public enum Role {
+    Borrower(BorrowerRole.class), Investor(InvestorRole.class);
+
+    private Class<? extends Customer> typeCst;
+
+    Role(Class<? extends Customer> typeCst) {
+        this.typeCst = typeCst;
+    }
+    private static final Logger logger = LoggerFactory.getLogger(Role.class);
+
+    @SuppressWarnings("unchecked")
+    <T extends CustomerRole>Optional<T> instance(){
+        Class<? extends Customer> typeCst = this.typeCst;
+        try {
+            return (Optional<T>) Optional.of(typeCst.newInstance());
+        } catch (InstantiationException | IllegalAccessException e) {
+            logger.error("error creating an object",e);
+        }
+        return Optional.empty();
+    }
+
+}