The pattern Role object (#1031)

* init repo for role object * add to init * add to init * add first impl * add pattern * add license * add changes
2026-05-14 18:58:44 +00:00 · 2019-10-26 18:58:40 +01:00
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+/*
+ * 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;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static com.iluwatar.roleobject.Role.*;
+
+/**
+ * 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 {@link Customer} object.
+ * The common superclass for customer-specific roles is provided by {@link CustomerRole},
+ * which also supports the {@link Customer} interface.
+ * <p>
+ * The {@link CustomerRole} class is abstract and not meant to be instantiated.
+ * Concrete subclasses of {@link CustomerRole}, for example {@link BorrowerRole} or {@link InvestorRole},
+ * define and implement the interface for specific roles. It is only
+ * these subclasses which are instantiated at runtime.
+ * The {@link BorrowerRole}  class defines the context-specific view of {@link Customer}  objects as needed by the loan department.
+ * It defines additional operations to manage the customer’s
+ * credits and securities. Similarly, the {@link InvestorRole} 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 {@link CustomerRole} class, using the interface class
+ * {@link Customer}, or with objects of concrete  {@link CustomerRole} subclasses. Suppose the loan application knows a particular
+ * {@link Customer} instance through its {@link Customer} interface. The loan application may want to check whether the {@link Customer}
+ * object plays the role of Borrower.
+ * To this end it calls {@link Customer#hasRole(Role)} with a suitable role specification. For the purpose of
+ * our example, let’s assume we can name roles with enum.
+ * If the {@link 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 {
+
+    private static final Logger logger = LoggerFactory.getLogger(Role.class);
+
+    public static void main(String[] args) {
+        Customer customer = Customer.newCustomer(Borrower, Investor);
+
+        logger.info(" the new customer created : {}", customer);
+
+        boolean hasBorrowerRole = customer.hasRole(Borrower);
+        logger.info(" customer has a borrowed role - {}", hasBorrowerRole);
+        boolean hasInvestorRole = customer.hasRole(Investor);
+        logger.info(" customer has an investor role - {}", hasInvestorRole);
+
+        customer.getRole(Investor, InvestorRole.class)
+                .ifPresent(inv -> {
+                    inv.setAmountToInvest(1000);
+                    inv.setName("Billy");
+                });
+        customer.getRole(Borrower, BorrowerRole.class)
+                .ifPresent(inv -> inv.setName("Johny"));
+
+        customer.getRole(Investor, InvestorRole.class)
+                .map(InvestorRole::invest)
+                .ifPresent(logger::info);
+
+        customer.getRole(Borrower, BorrowerRole.class)
+                .map(BorrowerRole::borrow)
+                .ifPresent(logger::info);
+    }
+
+
+}