BAEL-5134: an example of constructor chaining, added unit tests

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/constructorchaining/Customer.java

@@ -0,0 +1,34 @@
+package com.baeldung.constructorchaining;
+
+import java.util.Objects;
+
+public class Customer extends Person {
+    private final String loyaltyCardId;
+
+    public Customer(String firstName, String lastName, int age, String loyaltyCardId) {
+        this(firstName, null, lastName, age, loyaltyCardId);
+    }
+
+    public Customer(String firstName, String middleName, String lastName, int age, String loyaltyCardId) {
+        super(firstName, middleName, lastName, age);
+        this.loyaltyCardId = loyaltyCardId;
+    }
+
+    public String getLoyaltyCardId() {
+        return loyaltyCardId;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        if (!super.equals(o)) return false;
+        Customer customer = (Customer) o;
+        return Objects.equals(loyaltyCardId, customer.loyaltyCardId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(super.hashCode(), loyaltyCardId);
+    }
+}

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/constructorchaining/Person.java

@@ -0,0 +1,51 @@
+package com.baeldung.constructorchaining;
+
+import java.util.Objects;
+
+public class Person {
+    private final String firstName;
+    private final String middleName;
+    private final String lastName;
+    private final int age;
+
+    public Person(String firstName, String lastName, int age) {
+        this(firstName, null, lastName, age);
+    }
+
+
+    public Person(String firstName, String middleName, String lastName, int age) {
+        this.firstName = firstName;
+        this.middleName = middleName;
+        this.lastName = lastName;
+        this.age = age;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public String getMiddleName() {
+        return middleName;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Person person = (Person) o;
+        return age == person.age && Objects.equals(firstName, person.firstName) && Objects.equals(middleName, person.middleName) && Objects.equals(lastName, person.lastName);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(firstName, middleName, lastName, age);
+    }
+}

core-java-modules/core-java-lang-4/src/test/java/com/baeldung/constructorchaining/CustomerUnitTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.constructorchaining;
+
+import org.junit.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+public class CustomerUnitTest {
+
+    @Test
+    public void givenNameLastNameAndAge_whenUsingDedicatedConstructor_shouldInitializeFieldsAndNullifyMiddleName() {
+        Customer mark = new Customer("Mark", "Johnson", 23, "abcd1234");
+
+        assertEquals(23, mark.getAge());
+        assertEquals("Mark", mark.getFirstName());
+        assertEquals("Johnson", mark.getLastName());
+        assertEquals("abcd1234", mark.getLoyaltyCardId());
+        assertNull(mark.getMiddleName());
+    }
+
+    @Test
+    public void givenAllFieldsRequired_whenUsingDedicatedConstructor_shouldInitializeAllFields() {
+        Customer mark = new Customer("Mark", "Andrew", "Johnson", 23, "abcd1234");
+
+        assertEquals(23, mark.getAge());
+        assertEquals("Mark", mark.getFirstName());
+        assertEquals("Andrew", mark.getMiddleName());
+        assertEquals("Johnson", mark.getLastName());
+        assertEquals("abcd1234", mark.getLoyaltyCardId());
+    }
+}

core-java-modules/core-java-lang-4/src/test/java/com/baeldung/constructorchaining/PersonUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.constructorchaining;
+
+import org.junit.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+public class PersonUnitTest {
+
+    @Test
+    public void givenNameLastNameAndAge_whenUsingDedicatedConstructor_shouldInitializeFieldsAndNullifyMiddleName() {
+        Person mark = new Person("Mark", "Johnson", 23);
+
+        assertEquals(23, mark.getAge());
+        assertEquals("Mark", mark.getFirstName());
+        assertEquals("Johnson", mark.getLastName());
+        assertNull(mark.getMiddleName());
+    }
+
+    @Test
+    public void givenAllFieldsRequired_whenUsingDedicatedConstructor_shouldInitializeAllFields() {
+        Person mark = new Person("Mark", "Andrew", "Johnson", 23);
+
+        assertEquals(23, mark.getAge());
+        assertEquals("Mark", mark.getFirstName());
+        assertEquals("Andrew", mark.getMiddleName());
+        assertEquals("Johnson", mark.getLastName());
+    }
+}