BAEL-5819: java collections pecs

core-java-modules/core-java-collections-4/src/main/java/com/baeldung/collections/pecs/ProducerExtendsConsumerSupers.java

@@ -0,0 +1,59 @@
+package com.baeldung.collections.pecs;
+
+import java.util.Arrays;
+import java.util.List;
+
+import com.baeldung.collections.pecs.model.Customer;
+import com.baeldung.collections.pecs.model.Operator;
+import com.baeldung.collections.pecs.model.User;
+
+public class ProducerExtendsConsumerSupers {
+
+    public void producerExtends() {
+        List<Operator> operators = Arrays.asList(new Operator("sam"), new Operator("daniel"));
+        List<Customer> customers = Arrays.asList(new Customer("arys"), new Customer("cristiana"));
+
+        // sendEmails(operators); --> will not compile!
+        sendEmailsFixed(operators);
+        sendEmailsFixed(customers);
+    }
+
+    private void sendEmails(List<User> users) {
+        for (User user : users) {
+            System.out.println("sending email to " + user);
+        }
+    }
+
+    private void sendEmailsFixed(List<? extends User> users) {
+        for (User user : users) {
+            System.out.println("sending email to " + user);
+        }
+    }
+
+    public void consumerSupers() {
+        List<Operator> allOperators = Arrays.asList(new Operator("tom"));
+        List<User> allUsers = Arrays.asList(new Operator("tom"), new Customer("spencer"));
+
+        // addUsersFromMarketingDepartment(allUsers); --> will not compile!
+        addUsersFromMarketingDepartmentFixed(allOperators);
+        addUsersFromMarketingDepartmentFixed(allUsers);
+    }
+
+    private void addUsersFromMarketingDepartment(List<Operator> users) {
+        users.add(new Operator("john doe"));
+        users.add(new Operator("jane doe"));
+    }
+
+    private void addUsersFromMarketingDepartmentFixed(List<? super Operator> users) {
+        users.add(new Operator("john doe"));
+        users.add(new Operator("jane doe"));
+    }
+
+    private void addUsersAndSendEmails(List<User> users) {
+        users.add(new Operator("john doe"));
+        for (User user : users) {
+            System.out.println("sending email to: " + user);
+        }
+    }
+
+}

core-java-modules/core-java-collections-4/src/main/java/com/baeldung/collections/pecs/model/Customer.java

@@ -0,0 +1,7 @@
+package com.baeldung.collections.pecs.model;
+
+public class Customer extends User {
+    public Customer(String name) {
+        super(name);
+    }
+}

core-java-modules/core-java-collections-4/src/main/java/com/baeldung/collections/pecs/model/Operator.java

@@ -0,0 +1,7 @@
+package com.baeldung.collections.pecs.model;
+
+public class Operator extends User {
+    public Operator(String name) {
+        super(name);
+    }
+}

core-java-modules/core-java-collections-4/src/main/java/com/baeldung/collections/pecs/model/User.java

@@ -0,0 +1,9 @@
+package com.baeldung.collections.pecs.model;
+
+public class User {
+    private final String name;
+
+    public User(String name) {
+        this.name = name;
+    }
+}