BAEL-16653 (#7691)

* added module 'design-patterns-behavioral' * added module 'design-patterns-structural' * added module 'design-patterns-creational' * added module 'design-patterns-architectural' * added module 'design-patterns-functional' * moved facade code examples from design-patterns to design-patterns-structural * moved singleton examples from design-patterns to design-patterns-creational * moved bridge examples from design-patterns to design-patterns-structural * moved creational examples from design-patterns to design-patterns-creational * moved observer examples from design-patterns to design-patterns-behavioral * moved flyweight examples from design-patterns to design-patterns-creational * moved service locator examples from design-patterns to design-patterns-architectural * moved double checked locking singleton examples from design-patterns to design-patterns-creational * moved composite examples from design-patterns to design-patterns-structural * moved visitor examples from design-patterns to design-patterns-behavioral * moved dao examples from design-patterns to design-patterns-architectural * moved interpreter examples from design-patterns to design-patterns-behavioral * moved state examples from design-patterns to design-patterns-behavioral * moved decorator examples from design-patterns to design-patterns-structural * renamed LogerUtil to LoggerUtil * moved template method examples from design-patterns to design-patterns-behavioral * moved chain of responsibility examples from design-patterns to design-patterns-behavioral * moved command examples from design-patterns to design-patterns-behavioral * moved constructor vs static factory method examples from design-patterns to design-patterns-creational * moved adapter examples from design-patterns to design-patterns-structural * moved currying examples from design-patterns to design-patterns-functional * moved proxy examples from design-patterns to design-patterns-structural * moved persistence.xml from design-patterns to design-patterns-architectural * deleted empty module: design-patterns * moved mediator examples from design-patterns-2 to design-patterns-behavioral * moved null object examples from design-patterns-2 to design-patterns-behavioral * moved null check examples from design-patterns to design-patterns-behavioral * moved freebuilder examples from design-patterns-2 to design-patterns-creational * added module design-patterns-behavioral-2 * moved memento examples from design-patterns-2 to design-patterns-behavioral-2 * removed empty module design-patterns-2 * changed http to https in readmes in modules design-patterns-*
2019-09-11 13:00:16 +02:00
parent f4ec48e0b8
commit ff15a61559
215 changed files with 314 additions and 213 deletions
@@ -0,0 +1,8 @@
+### Relevant Articles:
+- [Singletons in Java](https://www.baeldung.com/java-singleton)
+- [Introduction to Creational Design Patterns](https://www.baeldung.com/creational-design-patterns)
+- [Abstract Factory Pattern in Java](https://www.baeldung.com/java-abstract-factory-pattern)
+- [Flyweight Pattern in Java](https://www.baeldung.com/java-flyweight)
+- [Double-Checked Locking with Singleton](https://www.baeldung.com/java-singleton-double-checked-locking)
+- [Java Constructors vs Static Factory Methods](https://www.baeldung.com/java-constructors-vs-static-factory-methods)
+- [Automatic Generation of the Builder Pattern with FreeBuilder](https://www.baeldung.com/java-builder-pattern-freebuilder)
@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>design-patterns-creational</artifactId>
+    <version>1.0</version>
+    <name>design-patterns-creational</name>
+	<packaging>jar</packaging>
+	
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>patterns</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>..</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.inferred</groupId>
+            <artifactId>freebuilder</artifactId>
+            <version>${freebuilder.version}</version>
+            <optional>true</optional>
+        </dependency>
+        <dependency>
+            <groupId>com.google.code.findbugs</groupId>
+            <artifactId>jsr305</artifactId>
+            <version>${javax.annotations.version}</version>
+        </dependency>
+        
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+	
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+        
+        <freebuilder.version>2.4.1</freebuilder.version>
+        <javax.annotations.version>3.0.2</javax.annotations.version>
+        <assertj-core.version>3.9.1</assertj-core.version>
+    </properties>
+</project>
@@ -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");
+    }
+}
@@ -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 volatile 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);
+    }
+}
@@ -0,0 +1,5 @@
+package com.baeldung.creational.abstractfactory;
+
+public interface AbstractFactory<T> {
+    T create(String type) ;
+}
@@ -0,0 +1,18 @@
+package com.baeldung.creational.abstractfactory;
+
+public class AbstractPatternDriver {
+    public static void main(String[] args) {
+        AbstractFactory abstractFactory;
+        
+        //creating a brown toy dog
+        abstractFactory = FactoryProvider.getFactory("Toy");
+        Animal toy =(Animal) abstractFactory.create("Dog");
+        
+        abstractFactory = FactoryProvider.getFactory("Color");
+        Color color =(Color) abstractFactory.create("Brown");
+        
+        String result = "A " + toy.getType() + " with " + color.getColor() + " color " + toy.makeSound();
+        
+        System.out.println(result);
+    }
+}
@@ -0,0 +1,6 @@
+package com.baeldung.creational.abstractfactory;
+
+public interface Animal {
+    String getType();
+    String makeSound();
+}
@@ -0,0 +1,16 @@
+package com.baeldung.creational.abstractfactory;
+
+public class AnimalFactory implements AbstractFactory<Animal> {
+
+    @Override
+    public Animal create(String animalType) {
+        if ("Dog".equalsIgnoreCase(animalType)) {
+            return new Dog();
+        } else if ("Duck".equalsIgnoreCase(animalType)) {
+            return new Duck();
+        }
+
+        return null;
+    }
+
+}
@@ -0,0 +1,10 @@
+package com.baeldung.creational.abstractfactory;
+
+public class Brown implements Color {
+
+    @Override
+    public String getColor() {
+        return "brown";
+    }
+
+}
@@ -0,0 +1,5 @@
+package com.baeldung.creational.abstractfactory;
+
+public interface Color {
+    String getColor();
+}
@@ -0,0 +1,16 @@
+package com.baeldung.creational.abstractfactory;
+
+public class ColorFactory implements AbstractFactory<Color> {
+
+    @Override
+    public Color create(String colorType) {
+        if ("Brown".equalsIgnoreCase(colorType)) {
+            return new Brown();
+        } else if ("White".equalsIgnoreCase(colorType)) {
+            return new White();
+        }
+
+        return null;
+    }
+
+}
@@ -0,0 +1,15 @@
+package com.baeldung.creational.abstractfactory;
+
+public class Dog implements Animal {
+
+    @Override
+    public String getType() {
+        return "Dog";
+    }
+
+    @Override
+    public String makeSound() {
+        return "Barks";
+    }
+
+}
@@ -0,0 +1,15 @@
+package com.baeldung.creational.abstractfactory;
+
+public class Duck implements Animal {
+
+    @Override
+    public String getType() {
+        return "Duck";
+    }
+
+    @Override
+    public String makeSound() {
+        return "Squeks";
+    }
+
+}
@@ -0,0 +1,15 @@
+package com.baeldung.creational.abstractfactory;
+
+public class FactoryProvider {
+    public static AbstractFactory getFactory(String choice){
+        
+        if("Toy".equalsIgnoreCase(choice)){
+            return new AnimalFactory();
+        }
+        else if("Color".equalsIgnoreCase(choice)){
+            return new ColorFactory();
+        }
+        
+        return null;
+    }
+}
@@ -0,0 +1,10 @@
+package com.baeldung.creational.abstractfactory;
+
+public class White implements Color {
+
+    @Override
+    public String getColor() {
+        return "White";
+    }
+
+}
@@ -0,0 +1,64 @@
+package com.baeldung.creational.builder;
+
+public class BankAccount {
+    private String name;
+    private String accountNumber;
+    private String email;
+    private boolean newsletter;
+
+    //The constructor that takes a builder from which it will create object
+    //the access to this is only provided to builder
+    private BankAccount(BankAccountBuilder builder) {
+        this.name = builder.name;
+        this.accountNumber = builder.accountNumber;
+        this.email = builder.email;
+        this.newsletter = builder.newsletter;
+    }
+    
+    public static class BankAccountBuilder {
+        private String name;
+        private String accountNumber;
+        private String email;
+        private boolean newsletter;
+        
+        //All Mandatory parameters goes with this constructor
+        public BankAccountBuilder(String name, String accountNumber) {
+            this.name = name;
+            this.accountNumber = accountNumber;
+        }
+
+        //setters for optional parameters which returns this same builder
+        //to support fluent design
+        public BankAccountBuilder withEmail(String email) {
+            this.email = email;
+            return this;
+        }
+
+        public BankAccountBuilder wantNewsletter(boolean newsletter) {
+            this.newsletter = newsletter;
+            return this;
+        }
+        
+        //the actual build method that prepares and returns a BankAccount object
+        public BankAccount build() {
+            return new BankAccount(this);
+        }
+    }
+
+    //getters
+    public String getName() {
+        return name;
+    }
+
+    public String getAccountNumber() {
+        return accountNumber;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public boolean isNewsletter() {
+        return newsletter;
+    }
+}
@@ -0,0 +1,16 @@
+package com.baeldung.creational.builder;
+
+public class BuilderPatternDriver {
+    public static void main(String[] args) {
+        BankAccount newAccount = new BankAccount
+          .BankAccountBuilder("Jon", "22738022275")
+          .withEmail("jon@example.com")
+          .wantNewsletter(true)
+          .build();
+
+        System.out.println("Name: " + newAccount.getName());
+        System.out.println("AccountNumber:" + newAccount.getAccountNumber());
+        System.out.println("Email: " + newAccount.getEmail());
+        System.out.println("Want News letter?: " + newAccount.isNewsletter());
+    }
+}
@@ -0,0 +1,16 @@
+package com.baeldung.creational.factory;
+
+public class FactoryDriver {
+    public static void main(String[] args) {
+        Polygon p;
+        PolygonFactory factory = new PolygonFactory();
+        
+        //get the shape which has 4 sides
+        p = factory.getPolygon(4);
+        System.out.println("The shape with 4 sides is a " + p.getType());
+        
+        //get the shape which has 4 sides
+        p = factory.getPolygon(8);
+        System.out.println("The shape with 8 sides is a " + p.getType());
+    }
+}
@@ -0,0 +1,10 @@
+package com.baeldung.creational.factory;
+
+public class Heptagon implements Polygon {
+
+    @Override
+    public String getType() {
+        return "Heptagon";
+    }
+
+}
@@ -0,0 +1,10 @@
+package com.baeldung.creational.factory;
+
+public class Octagon implements Polygon {
+
+    @Override
+    public String getType() {
+        return "Octagon";
+    }
+
+}
@@ -0,0 +1,10 @@
+package com.baeldung.creational.factory;
+
+public class Pentagon implements Polygon {
+
+    @Override
+    public String getType() {
+        return "Pentagon";
+    }
+
+}
@@ -0,0 +1,5 @@
+package com.baeldung.creational.factory;
+
+public interface Polygon {
+    String getType();
+}
@@ -0,0 +1,22 @@
+package com.baeldung.creational.factory;
+
+public class PolygonFactory {
+    public Polygon getPolygon(int numberOfSides) {
+        if(numberOfSides == 3) {
+            return new Triangle();
+        }
+        if(numberOfSides == 4) {
+            return new Square();
+        }
+        if(numberOfSides == 5) {
+            return new Pentagon();
+        }
+        if(numberOfSides == 7) {
+            return new Heptagon();
+        }
+        else if(numberOfSides == 8) {
+            return new Octagon();
+        }
+        return null;
+    }
+}
@@ -0,0 +1,10 @@
+package com.baeldung.creational.factory;
+
+public class Square implements Polygon {
+
+    @Override
+    public String getType() {
+        return "Square";
+    }
+
+}
@@ -0,0 +1,10 @@
+package com.baeldung.creational.factory;
+
+public class Triangle implements Polygon {
+
+    @Override
+    public String getType() {
+        return "Triangle";
+    }
+
+}
@@ -0,0 +1,13 @@
+package com.baeldung.creational.singleton;
+
+public class Singleton  {    
+    private Singleton() {}
+    
+    private static class SingletonHolder {    
+        public static final Singleton instance = new Singleton();
+    }    
+
+    public static Singleton getInstance() {    
+        return SingletonHolder.instance;    
+    }    
+}
@@ -0,0 +1,8 @@
+package com.baeldung.creational.singleton;
+
+public class SingletonDriver {
+    public static void main(String[] args) {
+        Singleton instance = Singleton.getInstance();
+        System.out.println(instance.toString());
+    }
+}
@@ -0,0 +1,82 @@
+package com.baeldung.flyweight;
+
+import java.awt.Color;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Represents a car. This class is immutable.
+ * 
+ * @author Donato Rimenti
+ */
+public class Car implements Vehicle {
+
+	/**
+	 * Logger.
+	 */
+	private final static Logger LOG = LoggerFactory.getLogger(Car.class);
+
+	/**
+	 * The car's engine.
+	 */
+	private Engine engine;
+
+	/**
+	 * The car's color.
+	 */
+	private Color color;
+
+	/**
+	 * Instantiates a new Car.
+	 *
+	 * @param engine
+	 *            the {@link #engine}
+	 * @param color
+	 *            the {@link #color}
+	 */
+	public Car(Engine engine, Color color) {
+		this.engine = engine;
+		this.color = color;
+
+		// Building a new car is a very expensive operation!
+		try {
+			Thread.sleep(2000);
+		} catch (InterruptedException e) {
+			LOG.error("Error while creating a new car", e);
+		}
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.baeldung.flyweight.Vehicle#start()
+	 */
+	@Override
+	public void start() {
+		LOG.info("Car is starting!");
+		engine.start();
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.baeldung.flyweight.Vehicle#stop()
+	 */
+	@Override
+	public void stop() {
+		LOG.info("Car is stopping!");
+		engine.stop();
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see com.baeldung.flyweight.Vehicle#getColor()
+	 */
+	@Override
+	public Color getColor() {
+		return this.color;
+	}
+
+}
@@ -0,0 +1,31 @@
+package com.baeldung.flyweight;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Engine for a vehicle.
+ * 
+ * @author Donato Rimenti
+ */
+public class Engine {
+
+	/**
+	 * Logger.
+	 */
+	private final static Logger LOG = LoggerFactory.getLogger(Engine.class);
+
+	/**
+	 * Starts the engine.
+	 */
+	public void start() {
+		LOG.info("Engine is starting!");
+	}
+
+	/**
+	 * Stops the engine.
+	 */
+	public void stop() {
+		LOG.info("Engine is stopping!");
+	}
+}
@@ -0,0 +1,29 @@
+package com.baeldung.flyweight;
+
+import java.awt.Color;
+
+/**
+ * Interface for a vehicle.
+ * 
+ * @author Donato Rimenti
+ */
+public interface Vehicle {
+
+	/**
+	 * Starts the vehicle.
+	 */
+	public void start();
+
+	/**
+	 * Stops the vehicle.
+	 */
+	public void stop();
+
+	/**
+	 * Gets the color of the vehicle.
+	 * 
+	 * @return the color of the vehicle
+	 */
+	public Color getColor();
+
+}
@@ -0,0 +1,45 @@
+package com.baeldung.flyweight;
+
+import java.awt.Color;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Factory which implements the Flyweight pattern to return an existing vehicle
+ * if present or a new one otherwise.
+ * 
+ * @author Donato Rimenti
+ */
+public class VehicleFactory {
+
+	/**
+	 * Stores the already created vehicles.
+	 */
+	private static Map<Color, Vehicle> vehiclesCache = new HashMap<Color, Vehicle>();
+
+	/**
+	 * Private constructor to prevent this class instantiation.
+	 */
+	private VehicleFactory() {
+	}
+
+	/**
+	 * Returns a vehicle of the same color passed as argument. If that vehicle
+	 * was already created by this factory, that vehicle is returned, otherwise
+	 * a new one is created and returned.
+	 * 
+	 * @param color
+	 *            the color of the vehicle to return
+	 * @return a vehicle of the specified color
+	 */
+	public static Vehicle createVehicle(Color color) {
+		// Looks for the requested vehicle into the cache.
+		// If the vehicle doesn't exist, a new one is created.
+		Vehicle newVehicle = vehiclesCache.computeIfAbsent(color, newColor -> {
+			// Creates the new car.
+			Engine newEngine = new Engine();
+			return new Car(newEngine, newColor);
+		});
+		return newVehicle;
+	}
+}
@@ -0,0 +1,25 @@
+package com.baeldung.freebuilder;
+
+import org.inferred.freebuilder.FreeBuilder;
+
+import java.util.Optional;
+
+@FreeBuilder
+public interface Address {
+
+    Optional<String> getAddressLine1();
+
+    Optional<String> getAddressLine2();
+
+    Optional<String> getAddressLine3();
+
+    String getCity();
+
+    Optional<String> getState();
+
+    Optional<Long> getPinCode();
+
+    class Builder extends Address_Builder {
+
+    }
+}
@@ -0,0 +1,65 @@
+package com.baeldung.freebuilder;
+
+import org.inferred.freebuilder.FreeBuilder;
+
+import javax.annotation.Nullable;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+@FreeBuilder
+public interface Employee {
+
+    String getName();
+
+    int getAge();
+
+    String getDepartment();
+
+    String getRole();
+
+    String getSupervisorName();
+
+    String getDesignation();
+
+    String getEmail();
+
+    long getPhoneNumber();
+
+    Optional<Boolean> getPermanent();
+
+    Optional<String> getDateOfJoining();
+
+    @Nullable
+    String getCurrentProject();
+
+    Address getAddress();
+
+    List<Long> getAccessTokens();
+
+    Map<String, Long> getAssetsSerialIdMapping();
+
+    Optional<Double> getSalaryInUSD();
+
+
+    class Builder extends Employee_Builder {
+
+        public Builder() {
+            // setting default value for department
+            setDepartment("Builder Pattern");
+        }
+
+        @Override
+        public Builder setEmail(String email) {
+            if (checkValidEmail(email))
+                return super.setEmail(email);
+            else
+                throw new IllegalArgumentException("Invalid email");
+
+        }
+
+        private boolean checkValidEmail(String email) {
+            return email.contains("@");
+        }
+    }
+}
@@ -0,0 +1,53 @@
+package com.baeldung.freebuilder.builder;
+
+public class Employee {
+
+    private final String name;
+    private final int age;
+    private final String department;
+
+    private Employee(String name, int age, String department) {
+        this.name = name;
+        this.age = age;
+        this.department = department;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public String getDepartment() {
+        return department;
+    }
+
+    public static class Builder {
+
+        private String name;
+        private int age;
+        private String department;
+
+        public Builder setName(String name) {
+            this.name = name;
+            return this;
+        }
+
+        public Builder setAge(int age) {
+            this.age = age;
+            return this;
+        }
+
+        public Builder setDepartment(String department) {
+            this.department = department;
+            return this;
+        }
+
+        public Employee build() {
+            return new Employee(name, age, department);
+        }
+    }
+
+}
@@ -0,0 +1,28 @@
+package com.baeldung.singleton;
+
+public class ClassSingleton {
+
+    private static ClassSingleton INSTANCE;
+    private String info = "Initial class info";
+    
+    private ClassSingleton(){        
+    }
+    
+    public static ClassSingleton getInstance(){
+        if(INSTANCE == null){
+            INSTANCE = new ClassSingleton();
+        }
+        
+        return INSTANCE;
+    }
+    
+    // getters and setters
+    
+    public String getInfo() {
+        return info;
+    }
+    
+    public void setInfo(String info) {
+        this.info = info;
+    }
+}
@@ -0,0 +1,26 @@
+package com.baeldung.singleton;
+
+public enum EnumSingleton {
+    
+    INSTANCE("Initial enum info"); //Name of the single instance
+    
+    private String info;
+    
+    private EnumSingleton(String info) {
+        this.info = info;
+    }
+    
+    public EnumSingleton getInstance(){
+        return INSTANCE;
+    }
+    
+    //getters and setters
+
+    public String getInfo() {
+        return info;
+    }
+
+    public void setInfo(String info) {
+        this.info = info;
+    }    
+}
@@ -0,0 +1,32 @@
+package com.baeldung.singleton;
+
+public class Sandbox {
+
+    public static void main(String[] args) {
+        
+        //Class singleton
+        
+        ClassSingleton classSingleton1 = ClassSingleton.getInstance();
+        //OurSingleton object1 = new OurSingleton(); // The constructor OurSingleton() is not visible
+        
+        System.out.println(classSingleton1.getInfo()); //Initial class info
+        
+        ClassSingleton classSingleton2 = ClassSingleton.getInstance();
+        classSingleton2.setInfo("New class info");
+        
+        System.out.println(classSingleton1.getInfo()); //New class info
+        System.out.println(classSingleton2.getInfo()); //New class info
+        
+        //Enum singleton
+        
+        EnumSingleton enumSingleton1 = EnumSingleton.INSTANCE.getInstance();
+        
+        System.out.println(enumSingleton1.getInfo()); //Initial enum info
+        
+        EnumSingleton enumSingleton2 = EnumSingleton.INSTANCE.getInstance();
+        enumSingleton2.setInfo("New enum info");
+        
+        System.out.println(enumSingleton1.getInfo()); //New enum info
+        System.out.println(enumSingleton2.getInfo()); //New enum info
+    }
+}
@@ -0,0 +1,38 @@
+package com.baeldung.singleton.synchronization;
+
+/**
+ * Double-checked locking design pattern applied to a singleton.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class DclSingleton {
+
+	/**
+	 * Current instance of the singleton.
+	 */
+	private static volatile DclSingleton instance;
+
+	/**
+	 * Private constructor to avoid instantiation.
+	 */
+	private DclSingleton() {
+	}
+
+	/**
+	 * Returns the current instance of the singleton.
+	 * 
+	 * @return the current instance of the singleton
+	 */
+	public static DclSingleton getInstance() {
+		if (instance == null) {
+			synchronized (DclSingleton.class) {
+				if (instance == null) {
+					instance = new DclSingleton();
+				}
+			}
+		}
+		return instance;
+	}
+
+}
@@ -0,0 +1,34 @@
+package com.baeldung.singleton.synchronization;
+
+/**
+ * Draconian singleton. The method to get the instance is synchronized.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class DraconianSingleton {
+
+	/**
+	 * Current instance of the singleton.
+	 */
+	private static DraconianSingleton instance;
+
+	/**
+	 * Private constructor to avoid instantiation.
+	 */
+	private DraconianSingleton() {
+	}
+
+	/**
+	 * Returns the current instance of the singleton.
+	 * 
+	 * @return the current instance of the singleton
+	 */
+	public static synchronized DraconianSingleton getInstance() {
+		if (instance == null) {
+			instance = new DraconianSingleton();
+		}
+		return instance;
+	}
+
+}
@@ -0,0 +1,31 @@
+package com.baeldung.singleton.synchronization;
+
+/**
+ * Singleton with early initialization. Inlines the singleton instance
+ * initialization.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class EarlyInitSingleton {
+
+	/**
+	 * Current instance of the singleton.
+	 */
+	private static final EarlyInitSingleton INSTANCE = new EarlyInitSingleton();
+
+	/**
+	 * Private constructor to avoid instantiation.
+	 */
+	private EarlyInitSingleton() {
+	}
+
+	/**
+	 * Returns the current instance of the singleton.
+	 * 
+	 * @return the current instance of the singleton
+	 */
+	public static EarlyInitSingleton getInstance() {
+		return INSTANCE;
+	}
+}
@@ -0,0 +1,16 @@
+package com.baeldung.singleton.synchronization;
+
+/**
+ * Enum singleton pattern. Uses an enum to hold a reference to the singleton
+ * instance.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public enum EnumSingleton {
+
+	/**
+	 * Current instance of the singleton.
+	 */
+	INSTANCE;
+}
@@ -0,0 +1,41 @@
+package com.baeldung.singleton.synchronization;
+
+/**
+ * Initialization on demand singleton pattern. Uses a nested static class to
+ * hold a reference to the singleton instance.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class InitOnDemandSingleton {
+
+	/**
+	 * Holder for a singleton instance.
+	 * 
+	 * @author Donato Rimenti
+	 *
+	 */
+	private static class InstanceHolder {
+
+		/**
+		 * Current instance of the singleton.
+		 */
+		private static final InitOnDemandSingleton INSTANCE = new InitOnDemandSingleton();
+	}
+
+	/**
+	 * Private constructor to avoid instantiation.
+	 */
+	private InitOnDemandSingleton() {
+	}
+
+	/**
+	 * Returns the current instance of the singleton.
+	 * 
+	 * @return the current instance of the singleton
+	 */
+	public static InitOnDemandSingleton getInstance() {
+		return InstanceHolder.INSTANCE;
+	}
+
+}
@@ -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);
+    }
+}
@@ -0,0 +1,23 @@
+package com.baeldung.creational.abstractfactory;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class AbstractPatternIntegrationTest {
+    @Test
+    public void givenAbstractFactory_whenGettingObjects_thenSuccessful() {
+        AbstractFactory abstractFactory;
+        
+        //creating a brown toy dog
+        abstractFactory = FactoryProvider.getFactory("Toy");
+        Animal toy = (Animal) abstractFactory.create("Dog");
+        
+        abstractFactory = FactoryProvider.getFactory("Color");
+        Color color =(Color) abstractFactory.create("Brown");
+        
+        String result = "A " + toy.getType() + " with " + color.getColor() + " color " + toy.makeSound();
+        assertEquals("A Dog with brown color Barks", result);
+    }
+
+}
@@ -0,0 +1,33 @@
+package com.baeldung.creational.builder;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class BuilderPatternIntegrationTest {
+    @Test
+    public void whenCreatingObjectThroughBuilder_thenObjectValid() {
+        BankAccount newAccount = new BankAccount
+          .BankAccountBuilder("Jon", "22738022275")
+          .withEmail("jon@example.com")
+          .wantNewsletter(true)
+          .build();
+        
+        assertEquals(newAccount.getName(), "Jon");
+        assertEquals(newAccount.getAccountNumber(), "22738022275");
+        assertEquals(newAccount.getEmail(), "jon@example.com");
+        assertEquals(newAccount.isNewsletter(), true);
+    }
+    
+    @Test
+    public void whenSkippingOptionalParameters_thenObjectValid() {
+        BankAccount newAccount = new BankAccount
+          .BankAccountBuilder("Jon", "22738022275")
+          .build();
+        
+        assertEquals(newAccount.getName(), "Jon");
+        assertEquals(newAccount.getAccountNumber(), "22738022275");
+        assertEquals(newAccount.getEmail(), null);
+        assertEquals(newAccount.isNewsletter(), false);
+    }
+}
@@ -0,0 +1,32 @@
+package com.baeldung.creational.factory;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class FactoryIntegrationTest {
+
+    @Test
+    public void whenUsingFactoryForSquare_thenCorrectObjectReturned() {
+        Polygon p;
+        PolygonFactory factory = new PolygonFactory();
+        
+        //get the shape which has 4 sides
+        p = factory.getPolygon(4);
+        String result = "The shape with 4 sides is a " + p.getType();
+        
+        assertEquals("The shape with 4 sides is a Square", result);
+    }
+    
+    @Test
+    public void whenUsingFactoryForOctagon_thenCorrectObjectReturned() {
+        Polygon p;
+        PolygonFactory factory = new PolygonFactory();
+        
+        //get the shape which has 4 sides
+        p = factory.getPolygon(8);
+        String result = "The shape with 8 sides is a " + p.getType();
+        
+        assertEquals("The shape with 8 sides is a Octagon", result);
+    }
+}
@@ -0,0 +1,26 @@
+package com.baeldung.creational.singleton;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class SingletonIntegrationTest {
+
+    @Test
+    /**
+     * Although there is absolutely no way to determine whether
+     * a class is Singleton, in this test case, we will just 
+     * check for two objects if they point to same instance or 
+     * not. We will also check for their hashcode.
+     */
+    public void whenGettingMultipleObjects_thenAllPointToSame() {
+        //first object
+        Singleton obj1 = Singleton.getInstance();
+        
+        //Second object
+        Singleton obj2 = Singleton.getInstance();
+        
+        assertTrue(obj1 == obj2);
+        assertEquals(obj1.hashCode(), obj2.hashCode());
+    }
+
+}
@@ -0,0 +1,42 @@
+package com.baeldung.flyweight;
+
+import java.awt.Color;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit test for {@link VehicleFactory}.
+ * 
+ * @author Donato Rimenti
+ */
+public class FlyweightUnitTest {
+
+	/**
+	 * Checks that when the {@link VehicleFactory} is asked to provide two
+	 * vehicles of different colors, the objects returned are different.
+	 */
+	@Test
+	public void givenDifferentFlyweightObjects_whenEquals_thenFalse() {
+		Vehicle blackVehicle = VehicleFactory.createVehicle(Color.BLACK);
+		Vehicle blueVehicle = VehicleFactory.createVehicle(Color.BLUE);
+
+		Assert.assertNotNull("Object returned by the factory is null!", blackVehicle);
+		Assert.assertNotNull("Object returned by the factory is null!", blueVehicle);
+		Assert.assertNotEquals("Objects returned by the factory are equals!", blackVehicle, blueVehicle);
+	}
+
+	/**
+	 * Checks that when the {@link VehicleFactory} is asked to provide two
+	 * vehicles of the same colors, the same object is returned twice.
+	 */
+	@Test
+	public void givenSameFlyweightObjects_whenEquals_thenTrue() {
+		Vehicle blackVehicle = VehicleFactory.createVehicle(Color.BLACK);
+		Vehicle anotherBlackVehicle = VehicleFactory.createVehicle(Color.BLACK);
+
+		Assert.assertNotNull("Object returned by the factory is null!", blackVehicle);
+		Assert.assertNotNull("Object returned by the factory is null!", anotherBlackVehicle);
+		Assert.assertEquals("Objects returned by the factory are not equals!", blackVehicle, anotherBlackVehicle);
+	}
+}
@@ -0,0 +1,226 @@
+package com.baeldung.freebuilder;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class EmployeeBuilderUnitTest {
+
+    private static final int PIN_CODE = 223344;
+    public static final String CITY_NAME = "New York";
+    public static final int INPUT_SALARY_EUROS = 10000;
+    public static final double EUROS_TO_USD_RATIO = 0.6;
+
+    @Test
+    public void whenBuildEmployeeWithAddress_thenReturnEmployeeWithValidAddress() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setPermanent(true)
+          .setRole("developer")
+          .setAddress(address)
+          .build();
+
+        // then
+        assertTrue(employee.getAddress().getCity().equalsIgnoreCase(CITY_NAME));
+
+    }
+
+    @Test
+    public void whenMapSalary_thenReturnEmployeeWithSalaryInUSD() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).setPinCode(PIN_CODE).build();
+
+        long salaryInEuros = INPUT_SALARY_EUROS;
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder
+          .setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setPermanent(true)
+          .setRole("developer")
+          .setAddress(address)
+          .mapSalaryInUSD(sal -> salaryInEuros * EUROS_TO_USD_RATIO)
+          .build();
+
+        // then
+        assertTrue(employee.getAddress().getPinCode().get() == PIN_CODE);
+
+    }
+
+    @Test
+    public void whenOptionalFields_thenReturnEmployeeWithEmptyValues() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setPermanent(true)
+          .setRole("developer")
+          .setAddress(address)
+          .build();
+
+        // then
+        assertTrue(employee.getPermanent().isPresent());
+        assertTrue(employee.getPermanent().get());
+        assertFalse(employee.getDateOfJoining().isPresent());
+
+    }
+
+    @Test
+    public void whenNullableFields_thenReturnEmployeeWithNullValueForField() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setNullablePermanent(null)
+          .setDateOfJoining(Optional.empty())
+          .setRole("developer")
+          .setAddress(address)
+          .build();
+
+        // then
+        assertNull(employee.getCurrentProject());
+
+    }
+
+    @Test
+    public void whenCollectionFields_thenReturnEmployeeWithValues() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setNullablePermanent(null)
+          .setDateOfJoining(Optional.empty())
+          .setRole("developer")
+          .addAccessTokens(1221819L)
+          .addAccessTokens(1223441L, 134567L)
+          .setAddress(address)
+          .build();
+
+        // then
+        assertTrue(employee.getAccessTokens().size() == 3);
+
+    }
+
+    @Test
+    public void whenMapFields_thenReturnEmployeeWithValues() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setNullablePermanent(null)
+          .setDateOfJoining(Optional.empty())
+          .setRole("developer")
+          .addAccessTokens(1221819L)
+          .addAccessTokens(1223441L, 134567L)
+          .putAssetsSerialIdMapping("Laptop", 12345L)
+          .setAddress(address)
+          .build();
+
+        // then
+        assertTrue(employee.getAssetsSerialIdMapping().size() == 1);
+
+    }
+
+    @Test
+    public void whenNestedBuilderTypes_thenReturnEmployeeWithValues() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setNullablePermanent(null)
+          .setDateOfJoining(Optional.empty())
+          .setRole("developer")
+          .addAccessTokens(1221819L)
+          .addAccessTokens(1223441L, 134567L)
+          .putAssetsSerialIdMapping("Laptop", 12345L)
+          .setAddress(address)
+          .mutateAddress(a -> a.setPinCode(112200))
+          .build();
+
+        // then
+        assertTrue(employee.getAssetsSerialIdMapping().size() == 1);
+
+    }
+
+    @Test()
+    public void whenPartialEmployeeWithValidEmail_thenReturnEmployeeWithEmail() {
+
+        // when
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setEmail("abc@xyz.com")
+          .buildPartial();
+
+        assertNotNull(employee.getEmail());
+    }
+
+}
@@ -0,0 +1,27 @@
+package com.baeldung.freebuilder.builder;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+
+class EmployeeBuilderUnitTest {
+
+    public static final String NAME = "baeldung";
+
+    @Test
+    public void whenBuildEmployee_thenReturnValidEmployee() {
+
+        // when
+        Employee.Builder emplBuilder = new Employee.Builder();
+
+        Employee employee = emplBuilder
+          .setName(NAME)
+          .setAge(12)
+          .setDepartment("Builder Pattern")
+          .build();
+
+        //then
+        Assertions.assertTrue(employee.getName().equalsIgnoreCase(NAME));
+    }
+
+}
@@ -0,0 +1,119 @@
+package com.baeldung.singleton.synchronization;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit tests for the singleton synchronization package with the same name.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class SingletonSynchronizationIntegrationTest {
+
+	/**
+	 * Size of the thread pools used.
+	 */
+	private static final int POOL_SIZE = 1_000;
+	
+	/**
+	 * Number of tasks to submit.
+	 */
+	private static final int TASKS_TO_SUBMIT = 1_000_000;
+
+	/**
+	 * Tests the thread-safety of {@link DraconianSingleton}.
+	 */
+	@Test
+	public void givenDraconianSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<DraconianSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(DraconianSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+	
+	/**
+	 * Tests the thread-safety of {@link DclSingleton}.
+	 */
+	@Test
+	public void givenDclSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<DclSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(DclSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link EarlyInitSingleton}.
+	 */
+	@Test
+	public void givenEarlyInitSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<EarlyInitSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(EarlyInitSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link InitOnDemandSingleton}.
+	 */
+	@Test
+	public void givenInitOnDemandSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<InitOnDemandSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(InitOnDemandSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link EnumSingleton}.
+	 */
+	@Test
+	public void givenEnumSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<EnumSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(EnumSingleton.INSTANCE));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+}