BAEL-2066 - Java Constructors vs Static Factory Methods (#4934)

* Initial Commit

* Update User.java

* Update UserUnitTest.java

* Update User.java - UserUnitTest.java

core-java/src/main/java/com/baeldung/constructorsstaticfactorymethods/application/Application.java

@@ -0,0 +1,12 @@
+package com.baeldung.constructorsstaticfactorymethods.application;
+
+import com.baeldung.constructorsstaticfactorymethods.entities.User;
+ 
+public class Application {
+
+    public static void main(String[] args) {
+        User user1 = User.createWithDefaultCountry("John", "john@domain.com");
+        User user2 = User.createWithLoggedInstantiationTime("John", "john@domain.com", "Argentina");
+        User user3 = User.getSingletonInstance("John", "john@domain.com", "Argentina");
+    }
+}

core-java/src/main/java/com/baeldung/constructorsstaticfactorymethods/entities/User.java

@@ -0,0 +1,63 @@
+package com.baeldung.constructorsstaticfactorymethods.entities;
+
+import java.time.LocalTime;
+import java.util.logging.ConsoleHandler;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import java.util.logging.SimpleFormatter;
+
+public class User {
+
+    private static User instance = null;
+    private static final Logger LOGGER = Logger.getLogger(User.class.getName());
+    private final String name;
+    private final String email;
+    private final String country;
+    
+    public static User createWithDefaultCountry(String name, String email) {
+        return new User(name, email, "Argentina");
+    }
+
+    public static User createWithLoggedInstantiationTime(String name, String email, String country) {
+        setLoggerProperties();
+        LOGGER.log(Level.INFO, "Creating User instance at : {0}", LocalTime.now());
+        return new User(name, email, country);
+    }
+
+    public static User getSingletonInstance(String name, String email, String country) {
+        if (instance == null) {
+            synchronized (User.class) {
+                if (instance == null) {
+                    instance = new User(name, email, country);
+                }
+            }
+        }
+        return instance;
+
+    }
+
+    private User(String name, String email, String country) {
+        this.name = name;
+        this.email = email;
+        this.country = country;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public String getCountry() {
+        return country;
+    }
+    
+    private static void setLoggerProperties() {
+        ConsoleHandler handler = new ConsoleHandler();
+        handler.setLevel(Level.INFO);
+        handler.setFormatter(new SimpleFormatter());
+        LOGGER.addHandler(handler);
+    }
+}

core-java/src/test/java/com/baeldung/constructorsstaticfactorymethods/UserUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.constructorsstaticfactorymethods;
+
+import com.baeldung.constructorsstaticfactorymethods.entities.User;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class UserUnitTest {
+    
+    @Test
+    public void givenUserClass_whenCalledcreateWithDefaultCountry_thenCorrect() {
+        assertThat(User.createWithDefaultCountry("John", "john@domain.com")).isInstanceOf(User.class);
+    }
+    
+    @Test
+    public void givenUserIntanceCreatedWithcreateWithDefaultCountry_whenCalledgetName_thenCorrect() {
+        User user = User.createWithDefaultCountry("John", "john@domain.com");
+        assertThat(user.getName()).isEqualTo("John");
+    }
+    
+    @Test
+    public void givenUserIntanceCreatedWithcreateWithDefaultCountry_whenCalledgetEmail_thenCorrect() {
+        User user = User.createWithDefaultCountry("John", "john@domain.com");
+        assertThat(user.getEmail()).isEqualTo("john@domain.com");
+    }
+    
+    @Test
+    public void givenUserIntanceCreatedWithcreateWithDefaultCountry_whenCalledgetCountry_thenCorrect() {
+        User user = User.createWithDefaultCountry("John", "john@domain.com");
+        assertThat(user.getCountry()).isEqualTo("Argentina");
+    }
+    
+    @Test
+    public void givenUserInstanceCreatedWithcreateWithInstantiationTime_whenCalledcreateWithInstantiationTime_thenCorrect() {
+        assertThat(User.createWithLoggedInstantiationTime("John", "john@domain.com", "Argentina")).isInstanceOf(User.class);
+    }
+    
+    @Test
+    public void givenUserInstanceCreatedWithgetSingletonIntance_whenCalledgetSingletonInstance_thenCorrect() {
+        User user1 = User.getSingletonInstance("John", "john@domain.com", "Argentina");
+        User user2 = User.getSingletonInstance("John", "john@domain.com", "Argentina");
+        assertThat(user1).isEqualTo(user2);
+    }
+}