Merge branch 'master' of https://github.com/JonCook/tutorials

patterns/dipmodular/README.md

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+## Relevant Articles:
+
+- [The Dependency Inversion Principle in Java](https://www.baeldung.com/java-dependency-inversion-principle)

patterns/dipmodular/com.baeldung.dip.daoimplementations/com/baeldung/dip/daoimplementations/SimpleCustomerDao.java

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+package com.baeldung.dip.daoimplementations;
+
+import com.baeldung.dip.daos.CustomerDao;
+import com.baeldung.dip.entities.Customer;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+public class SimpleCustomerDao implements CustomerDao {
+
+    private Map<Integer, Customer> customers = new HashMap<>();
+
+    public SimpleCustomerDao() {
+
+    }
+
+    public SimpleCustomerDao(Map<Integer, Customer> customers) {
+        this.customers = customers;
+    }
+
+    @Override
+    public Optional<Customer> findById(int id) {
+        return Optional.ofNullable(customers.get(id));
+    }
+
+    @Override
+    public List<Customer> findAll() {
+        return new ArrayList<>(customers.values());
+    }
+}

patterns/dipmodular/com.baeldung.dip.daoimplementations/module-info.java

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+module com.baeldung.dip.daoimplementations {
+    requires com.baeldung.dip.entities;
+    requires com.baeldung.dip.daos;
+    provides com.baeldung.dip.daos.CustomerDao with com.baeldung.dip.daoimplementations.SimpleCustomerDao;
+    exports com.baeldung.dip.daoimplementations;
+}

patterns/dipmodular/com.baeldung.dip.daos/com/baeldung/dip/daos/CustomerDao.java

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+package com.baeldung.dip.daos;
+
+import com.baeldung.dip.entities.Customer;
+import java.util.Map;
+import java.util.Optional;
+
+public interface CustomerDao {
+
+    Optional<Customer> findById(int id);
+
+    List<Customer> findAll();
+
+}

patterns/dipmodular/com.baeldung.dip.daos/module-info.java

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+module com.baeldung.dip.daos {
+    requires com.baeldung.dip.entities;
+    exports com.baeldung.dip.daos;
+}

patterns/dipmodular/com.baeldung.dip.entities/com/baeldung/dip/entities/Customer.java

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+package com.baeldung.dip.entities;
+
+public class Customer {
+
+    private final String name;
+
+    public Customer(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public String toString() {
+        return "Customer{" + "name=" + name + '}';
+    }
+}

patterns/dipmodular/com.baeldung.dip.entities/module-info.java

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+module com.baeldung.dip.entities {
+    exports com.baeldung.dip.entities;
+}

patterns/dipmodular/com.baeldung.dip.mainapp/com/baeldung/dip/mainapp/MainApplication.java

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+package com.baeldung.dip.mainapp;
+
+import com.baeldung.dip.daoimplementations.MapCustomerDao;
+import com.baeldung.dip.entities.Customer;
+import com.baeldung.dip.services.CustomerService;
+import java.util.HashMap;
+
+public class MainApplication {
+
+    public static void main(String args[]) {
+        var customers = new HashMap<Integer, Customer>();
+        customers.put(1, new Customer("John"));
+        customers.put(2, new Customer("Susan"));
+        CustomerService customerService = new CustomerService(new SimpleCustomerDao(customers));
+        customerService.findAll().forEach(System.out::println);
+    }
+}

patterns/dipmodular/com.baeldung.dip.mainapp/module-info.java

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+module com.baeldung.dip.mainapp {
+    requires com.baeldung.dip.entities;
+    requires com.baeldung.dip.daos;
+    requires com.baeldung.dip.daoimplementations;
+    requires com.baeldung.dip.services;
+    exports com.baeldung.dip.mainapp;
+}

patterns/dipmodular/com.baeldung.dip.services/com/baeldung/dip/services/CustomerService.java

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+package com.baeldung.dip.services;
+
+import com.baeldung.dip.daos.CustomerDao;
+import com.baeldung.dip.entities.Customer;
+import java.util.Map;
+import java.util.Optional;
+
+public class CustomerService {
+
+    private final CustomerDao customerDao;
+
+    public CustomerService(CustomerDao customerDao) {
+        this.customerDao = customerDao;
+    }
+
+    public Optional<Customer> findById(int id) {
+        return customerDao.findById(id);
+    }
+
+    public List<Customer> findAll() {
+        return customerDao.findAll();
+    }
+}

patterns/dipmodular/com.baeldung.dip.services/module-info.java

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+module com.baeldung.dip.services {
+    requires com.baeldung.dip.entities;
+    requires com.baeldung.dip.daos;
+    uses com.baeldung.dip.daos.CustomerDao;
+    exports com.baeldung.dip.services;
+}