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

core-java-modules/core-java-lang-oop/.gitignore

@@ -0,0 +1,26 @@
+*.class
+
+0.*
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+.resourceCache
+
+# Packaged files #
+*.jar
+*.war
+*.ear
+
+# Files generated by integration tests
+*.txt
+backup-pom.xml
+/bin/
+/temp
+
+#IntelliJ specific
+.idea/
+*.iml

core-java-modules/core-java-lang-oop/README.md

@@ -0,0 +1,16 @@
+## Core Java Lang OOP
+
+This module contains articles about Object-oriented programming (OOP) in Java
+
+### Relevant Articles: 
+- [Guide to hashCode() in Java](https://www.baeldung.com/java-hashcode)
+- [A Guide to the Static Keyword in Java](https://www.baeldung.com/java-static)
+- [Polymorphism in Java](https://www.baeldung.com/java-polymorphism)
+- [Method Overloading and Overriding in Java](https://www.baeldung.com/java-method-overload-override)
+- [How to Make a Deep Copy of an Object in Java](https://www.baeldung.com/java-deep-copy)
+- [Guide to Inheritance in Java](https://www.baeldung.com/java-inheritance)
+- [Object Type Casting in Java](https://www.baeldung.com/java-type-casting)
+- [The “final” Keyword in Java](https://www.baeldung.com/java-final)
+- [Type Erasure in Java Explained](https://www.baeldung.com/java-type-erasure)
+- [Variable and Method Hiding in Java](https://www.baeldung.com/java-variable-method-hiding)
+- [[More -->]](/core-java-modules/core-java-lang-oop-2)

core-java-modules/core-java-lang-oop/pom.xml

@@ -0,0 +1,59 @@
+<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>core-java-lang-oop</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-lang-oop</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <!-- web -->
+        <!-- marshalling -->
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>${gson.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-lang-oop</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <gson.version>2.8.2</gson.version>
+        <!-- testing -->
+        <assertj-core.version>3.10.0</assertj-core.version>
+    </properties>
+
+</project>

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/casting/Animal.java

@@ -0,0 +1,13 @@
+package com.baeldung.casting;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Animal {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Animal.class);
+
+    public void eat() {
+        LOGGER.info("animal is eating");
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/casting/AnimalFeeder.java

@@ -0,0 +1,23 @@
+package com.baeldung.casting;
+
+import java.util.List;
+
+public class AnimalFeeder {
+
+    public void feed(List<Animal> animals) {
+        animals.forEach(animal -> {
+            animal.eat();
+            if (animal instanceof Cat) {
+                ((Cat) animal).meow();
+            }
+        });
+    }
+
+    public void uncheckedFeed(List<Animal> animals) {
+        animals.forEach(animal -> {
+            animal.eat();
+            ((Cat) animal).meow();
+        });
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/casting/AnimalFeederGeneric.java

@@ -0,0 +1,24 @@
+package com.baeldung.casting;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class AnimalFeederGeneric<T> {
+    private Class<T> type;
+
+    public AnimalFeederGeneric(Class<T> type) {
+        this.type = type;
+    }
+
+    public List<T> feed(List<Animal> animals) {
+        List<T> list = new ArrayList<T>();
+        animals.forEach(animal -> {
+            if (type.isInstance(animal)) {
+                T objAsType = type.cast(animal);
+                list.add(objAsType);
+            }
+        });
+        return list;
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/casting/Cat.java

@@ -0,0 +1,16 @@
+package com.baeldung.casting;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Cat extends Animal implements Mew {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Cat.class);
+
+    public void eat() {
+        LOGGER.info("cat is eating");
+    }
+
+    public void meow() {
+        LOGGER.info("meow");
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/casting/Dog.java

@@ -0,0 +1,12 @@
+package com.baeldung.casting;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Dog extends Animal {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Dog.class);
+
+    public void eat() {
+        LOGGER.info("dog is eating");
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/casting/Mew.java

@@ -0,0 +1,5 @@
+package com.baeldung.casting;
+
+public interface Mew {
+    public void meow();
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/deepcopy/Address.java

@@ -0,0 +1,59 @@
+package com.baeldung.deepcopy;
+
+import java.io.Serializable;
+
+public class Address implements Serializable, Cloneable {
+
+    @Override
+    public Object clone() {
+        try {
+            return (Address) super.clone();
+        } catch (CloneNotSupportedException e) {
+            return new Address(this.street, this.getCity(), this.getCountry());
+        }
+    }
+
+    private static final long serialVersionUID = 1740913841244949416L;
+    private String street;
+    private String city;
+
+    private String country;
+
+    public Address(Address that) {
+        this(that.getStreet(), that.getCity(), that.getCountry());
+    }
+
+    public Address(String street, String city, String country) {
+        this.street = street;
+        this.city = city;
+        this.country = country;
+    }
+
+    public Address() {
+    }
+
+    public String getStreet() {
+        return street;
+    }
+
+    public String getCity() {
+        return city;
+    }
+
+    public String getCountry() {
+        return country;
+    }
+
+    public void setStreet(String street) {
+        this.street = street;
+    }
+
+    public void setCity(String city) {
+        this.city = city;
+    }
+
+    public void setCountry(String country) {
+        this.country = country;
+    }
+}
+

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/deepcopy/User.java

@@ -0,0 +1,48 @@
+package com.baeldung.deepcopy;
+
+import java.io.Serializable;
+
+public class User implements Serializable, Cloneable {
+
+    private static final long serialVersionUID = -3427002229954777557L;
+    private String firstName;
+    private String lastName;
+    private Address address;
+
+    public User(String firstName, String lastName, Address address) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+        this.address = address;
+    }
+
+    public User(User that) {
+        this(that.getFirstName(), that.getLastName(), new Address(that.getAddress()));
+    }
+
+    public User() {
+    }
+
+    @Override
+    public Object clone() {
+        User user;
+        try {
+            user = (User) super.clone();
+        } catch (CloneNotSupportedException e) {
+            user = new User(this.getFirstName(), this.getLastName(), this.getAddress());
+        }
+        user.address = (Address) this.address.clone();
+        return user;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/finalkeyword/BlackCat.java

@@ -0,0 +1,5 @@
+package com.baeldung.finalkeyword;
+
+public class BlackCat {
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/finalkeyword/BlackDog.java

@@ -0,0 +1,6 @@
+package com.baeldung.finalkeyword;
+
+public class BlackDog extends Dog {
+    // public void sound() {
+    // }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/finalkeyword/Cat.java

@@ -0,0 +1,18 @@
+package com.baeldung.finalkeyword;
+
+public final class Cat {
+
+    private int weight;
+
+    public int getWeight() {
+        return weight;
+    }
+
+    public void setWeight(int weight) {
+        this.weight = weight;
+    }
+
+    public void methodWithFinalArguments(final int x) {
+        // x=1;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/finalkeyword/Dog.java

@@ -0,0 +1,7 @@
+package com.baeldung.finalkeyword;
+
+public class Dog {
+    
+    public final void sound() {
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/hashcode/entities/User.java

@@ -0,0 +1,42 @@
+package com.baeldung.hashcode.entities;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class User {
+
+    private final Logger logger = LoggerFactory.getLogger(User.class);
+    private long id;
+    private String name;
+    private String email;
+
+    public User(long id, String name, String email) {
+        this.id = id;
+        this.name = name;
+        this.email = email;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null)
+            return false;
+        if (this.getClass() != o.getClass())
+            return false;
+        User user = (User) o;
+        return id == user.id && (name.equals(user.name) && email.equals(user.email));
+    }
+
+    @Override
+    public int hashCode() {
+        int hash = 7;
+        hash = 31 * hash + (int) id;
+        hash = 31 * hash + (name == null ? 0 : name.hashCode());
+        hash = 31 * hash + (email == null ? 0 : email.hashCode());
+        logger.info("hashCode() method called - Computed hash: " + hash);
+        return hash;
+    }
+    // getters and setters here
+    
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/inheritance/ArmoredCar.java

@@ -0,0 +1,43 @@
+package com.baeldung.inheritance;
+
+public class ArmoredCar extends Car implements Floatable, Flyable{
+    private int bulletProofWindows;
+    private String model;
+    
+    public void remoteStartCar() {
+        // this vehicle can be started by using a remote control
+    }
+    
+    public String registerModel() {
+        return model;
+    }
+    
+    public String getAValue() {
+        return super.model;   // returns value of model defined in base class Car
+        // return this.model;   // will return value of model defined in ArmoredCar
+        // return model;   // will return value of model defined in ArmoredCar
+    }
+    
+    public static String msg() {
+    	// return super.msg(); // this won't compile.
+    	return "ArmoredCar"; 
+    }
+    
+	@Override
+    public void floatOnWater() {
+        System.out.println("I can float!");
+    }
+    
+	@Override
+    public void fly() {
+        System.out.println("I can fly!");
+    }
+    
+    public void aMethod() {
+        // System.out.println(duration); // Won't compile
+        System.out.println(Floatable.duration); // outputs 10
+        System.out.println(Flyable.duration); // outputs 20
+    }
+    
+    
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/inheritance/BMW.java

@@ -0,0 +1,12 @@
+package com.baeldung.inheritance;
+
+public class BMW extends Car {
+    public BMW() {
+    	super(5, "BMW");
+    }
+	
+	@Override
+    public String toString() {
+    	return model;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/inheritance/Car.java

@@ -0,0 +1,32 @@
+package com.baeldung.inheritance;
+
+public class Car {
+	private final int DEFAULT_WHEEL_COUNT = 5;
+	private final String DEFAULT_MODEL = "Basic";
+
+	protected int wheels;
+    protected String model;
+    
+    public Car() {
+    	this.wheels = DEFAULT_WHEEL_COUNT;
+    	this.model = DEFAULT_MODEL;
+    }
+    
+    public Car(int wheels, String model) {
+    	this.wheels = wheels;
+    	this.model = model;
+    }
+        
+    public void start() {
+        // Check essential parts
+        // If okay, start.
+    }
+    public static int count = 10;
+    public static String msg() {
+        return "Car";
+    }
+    
+    public String toString() {
+    	return model;
+    } 
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/inheritance/Employee.java

@@ -0,0 +1,15 @@
+package com.baeldung.inheritance;
+
+public class Employee {
+    private String name;
+    private Car car;
+    
+    public Employee(String name, Car car) {
+        this.name = name;
+        this.car = car;
+    }
+    
+    public Car getCar() {
+    	return car;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/inheritance/Floatable.java

@@ -0,0 +1,10 @@
+package com.baeldung.inheritance;
+
+public interface Floatable {
+    int duration = 10;
+    void floatOnWater();
+    
+    default void repair() {
+        System.out.println("Repairing Floatable object");   
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/inheritance/Flyable.java

@@ -0,0 +1,13 @@
+package com.baeldung.inheritance;
+
+public interface Flyable {
+    int duration = 10;
+    void fly();
+    
+    /*
+     * Commented 
+     */
+    //default void repair() {
+    //    System.out.println("Repairing Flyable object"); 
+    //}
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/inheritance/SpaceCar.java

@@ -0,0 +1,18 @@
+package com.baeldung.inheritance;
+
+public class SpaceCar extends Car implements SpaceTraveller {
+	@Override
+    public void floatOnWater() {
+        System.out.println("SpaceCar floating!");
+    }
+    
+	@Override
+    public void fly() {
+        System.out.println("SpaceCar flying!");
+    }
+    
+	@Override
+    public void remoteControl() {
+        System.out.println("SpaceCar being controlled remotely!");
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/inheritance/SpaceTraveller.java

@@ -0,0 +1,6 @@
+package com.baeldung.inheritance;
+
+public interface SpaceTraveller extends Floatable, Flyable {
+    int duration = 10;
+    void remoteControl();
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/initializationguide/User.java

@@ -0,0 +1,53 @@
+package com.baeldung.initializationguide;
+
+import java.io.Serializable;
+
+public class User implements Serializable, Cloneable {
+    private static final long serialVersionUID = 1L;
+    static String forum;
+    private String name;
+    private int id;
+
+    {
+        id = 0;
+        System.out.println("Instance Initializer");
+    }
+
+    static {
+    	forum = "Java";
+        System.out.println("Static Initializer");
+    }
+
+    public User(String name, int id) {
+        super();
+        this.name = name;
+        this.id = id;
+    }
+
+    public User() {
+        System.out.println("Constructor");
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    @Override
+    protected Object clone() throws CloneNotSupportedException {
+        return this;
+    }
+
+}
+

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/methodoverloadingoverriding/application/Application.java

@@ -0,0 +1,26 @@
+package com.baeldung.methodoverloadingoverriding.application;
+
+import com.baeldung.methodoverloadingoverriding.model.Car;
+import com.baeldung.methodoverloadingoverriding.model.Vehicle;
+import com.baeldung.methodoverloadingoverriding.util.Multiplier;
+
+public class Application {
+    
+    public static void main(String[] args) {
+        Multiplier multiplier = new Multiplier();
+        System.out.println(multiplier.multiply(10, 10));
+        System.out.println(multiplier.multiply(10, 10, 10));
+        System.out.println(multiplier.multiply(10, 10.5));
+        System.out.println(multiplier.multiply(10.5, 10.5));
+        
+        Vehicle vehicle = new Vehicle();
+        System.out.println(vehicle.accelerate(100));
+        System.out.println(vehicle.run());
+        System.out.println(vehicle.stop());
+        
+        Vehicle car = new Car();
+        System.out.println(car.accelerate(80));
+        System.out.println(car.run());
+        System.out.println(car.stop());
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/methodoverloadingoverriding/model/Car.java

@@ -0,0 +1,9 @@
+package com.baeldung.methodoverloadingoverriding.model;
+
+public class Car extends Vehicle {
+
+    @Override
+    public String accelerate(long mph) {
+        return "The car accelerates at : " + mph + " MPH.";
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/methodoverloadingoverriding/model/Vehicle.java

@@ -0,0 +1,16 @@
+package com.baeldung.methodoverloadingoverriding.model;
+
+public class Vehicle {
+    
+    public String accelerate(long mph) {
+        return "The vehicle accelerates at : " + mph + " MPH.";
+    }
+    
+    public String stop() {
+        return "The vehicle has stopped.";
+    }
+    
+    public String run() {
+        return "The vehicle is running.";
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/methodoverloadingoverriding/util/Multiplier.java

@@ -0,0 +1,16 @@
+package com.baeldung.methodoverloadingoverriding.util;
+
+public class Multiplier {
+    
+    public int multiply(int a, int b) {
+        return a * b;
+    }
+    
+    public int multiply(int a, int b, int c) {
+        return a * b * c;
+    }
+    
+    public double multiply(double a, double b) {
+        return a * b;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/polymorphism/FileManager.java

@@ -0,0 +1,38 @@
+package com.baeldung.polymorphism;
+
+import java.awt.image.BufferedImage;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class FileManager {
+
+    final static Logger logger = LoggerFactory.getLogger(FileManager.class);
+
+    public static void main(String[] args) {
+        GenericFile file1 = new TextFile("SampleTextFile", "This is a sample text content", "v1.0.0");
+        logger.info("File Info: \n" + file1.getFileInfo() + "\n");
+        ImageFile imageFile = new ImageFile("SampleImageFile", 200, 100, new BufferedImage(100, 200, BufferedImage.TYPE_INT_RGB).toString()
+            .getBytes(), "v1.0.0");
+        logger.info("File Info: \n" + imageFile.getFileInfo());
+    }
+
+    public static ImageFile createImageFile(String name, int height, int width, byte[] content, String version) {
+        ImageFile imageFile = new ImageFile(name, height, width, content, version);
+        logger.info("File 2 Info: \n" + imageFile.getFileInfo());
+        return imageFile;
+    }
+
+    public static GenericFile createTextFile(String name, String content, String version) {
+        GenericFile file1 = new TextFile(name, content, version);
+        logger.info("File 1 Info: \n" + file1.getFileInfo() + "\n");
+        return file1;
+    }
+    
+    public static TextFile createTextFile2(String name, String content, String version) {
+        TextFile file1 = new TextFile(name, content, version);
+        logger.info("File 1 Info: \n" + file1.getFileInfo() + "\n");
+        return file1;
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/polymorphism/GenericFile.java

@@ -0,0 +1,63 @@
+package com.baeldung.polymorphism;
+
+import java.util.Date;
+
+public class GenericFile {
+    private String name;
+    private String extension;
+    private Date dateCreated;
+    private String version;
+    private byte[] content;
+
+    public GenericFile() {
+        this.setDateCreated(new Date());
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getExtension() {
+        return extension;
+    }
+
+    public void setExtension(String extension) {
+        this.extension = extension;
+    }
+
+    public Date getDateCreated() {
+        return dateCreated;
+    }
+
+    public void setDateCreated(Date dateCreated) {
+        this.dateCreated = dateCreated;
+    }
+
+    public String getVersion() {
+        return version;
+    }
+
+    public void setVersion(String version) {
+        this.version = version;
+    }
+
+    public byte[] getContent() {
+        return content;
+    }
+
+    public void setContent(byte[] content) {
+        this.content = content;
+    }
+
+    public String getFileInfo() {
+        return "Generic File Impl";
+    }
+
+    public Object read() {
+        return content;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/polymorphism/ImageFile.java

@@ -0,0 +1,41 @@
+package com.baeldung.polymorphism;
+
+public class ImageFile extends GenericFile {
+    private int height;
+    private int width;
+
+    public ImageFile(String name, int height, int width, byte[] content, String version) {
+        this.setHeight(height);
+        this.setWidth(width);
+        this.setContent(content);
+        this.setName(name);
+        this.setVersion(version);
+        this.setExtension(".jpg");
+    }
+
+    public int getHeight() {
+        return height;
+    }
+
+    public void setHeight(int height) {
+        this.height = height;
+    }
+
+    public int getWidth() {
+        return width;
+    }
+
+    public void setWidth(int width) {
+        this.width = width;
+    }
+
+    public String getFileInfo() {
+        return "Image File Impl";
+    }
+
+    public String read() {
+        return this.getContent()
+            .toString();
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/polymorphism/TextFile.java

@@ -0,0 +1,44 @@
+package com.baeldung.polymorphism;
+
+public class TextFile extends GenericFile {
+    private int wordCount;
+
+    public TextFile(String name, String content, String version) {
+        String[] words = content.split(" ");
+        this.setWordCount(words.length > 0 ? words.length : 1);
+        this.setContent(content.getBytes());
+        this.setName(name);
+        this.setVersion(version);
+        this.setExtension(".txt");
+    }
+
+    public int getWordCount() {
+        return wordCount;
+    }
+
+    public void setWordCount(int wordCount) {
+        this.wordCount = wordCount;
+    }
+
+    public String getFileInfo() {
+        return "Text File Impl";
+    }
+
+    public String read() {
+        return this.getContent()
+            .toString();
+    }
+
+    public String read(int limit) {
+        return this.getContent()
+            .toString()
+            .substring(0, limit);
+    }
+
+    public String read(int start, int stop) {
+        return this.getContent()
+            .toString()
+            .substring(start, stop);
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/scope/method/BaseMethodClass.java

@@ -0,0 +1,9 @@
+package com.baeldung.scope.method;
+
+
+public class BaseMethodClass {
+
+    public static void printMessage() {
+        System.out.println("base static method");
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/scope/method/ChildMethodClass.java

@@ -0,0 +1,9 @@
+package com.baeldung.scope.method;
+
+
+public class ChildMethodClass extends BaseMethodClass {
+
+    public static void printMessage() {
+        System.out.println("child static method");
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/scope/method/MethodHidingDemo.java

@@ -0,0 +1,8 @@
+package com.baeldung.scope.method;
+
+public class MethodHidingDemo {
+
+    public static void main(String[] args) {
+        ChildMethodClass.printMessage();
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/scope/variable/ChildVariable.java

@@ -0,0 +1,13 @@
+package com.baeldung.scope.variable;
+
+/**
+ * Created by Gebruiker on 5/7/2018.
+ */
+public class ChildVariable extends ParentVariable {
+
+    String instanceVariable = "child variable";
+
+    public void printInstanceVariable() {
+        System.out.println(instanceVariable);
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/scope/variable/HideVariable.java

@@ -0,0 +1,23 @@
+package com.baeldung.scope.variable;
+
+/**
+ * Created by Gebruiker on 5/6/2018.
+ */
+public class HideVariable {
+
+    private String message = "this is instance variable";
+
+    HideVariable() {
+        String message = "constructor local variable";
+        System.out.println(message);
+    }
+
+    public void printLocalVariable() {
+        String message = "method local variable";
+        System.out.println(message);
+    }
+
+    public void printInstanceVariable() {
+        System.out.println(this.message);
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/scope/variable/ParentVariable.java

@@ -0,0 +1,13 @@
+package com.baeldung.scope.variable;
+
+/**
+ * Created by Gebruiker on 5/7/2018.
+ */
+public class ParentVariable {
+
+    String instanceVariable = "parent variable";
+
+    public void printInstanceVariable() {
+        System.out.println(instanceVariable);
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/scope/variable/VariableHidingDemo.java

@@ -0,0 +1,18 @@
+package com.baeldung.scope.variable;
+
+/**
+ * Created by Gebruiker on 5/6/2018.
+ */
+public class VariableHidingDemo {
+    public static void main(String[] args) {
+        HideVariable variable = new HideVariable();
+        variable.printLocalVariable();
+        variable.printInstanceVariable();
+
+        ParentVariable parentVariable = new ParentVariable();
+        ParentVariable childVariable = new ChildVariable();
+
+        parentVariable.printInstanceVariable();
+        childVariable.printInstanceVariable();
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/staticdemo/Car.java

@@ -0,0 +1,48 @@
+package com.baeldung.staticdemo;
+
+/**
+ * This class demonstrates the use of static fields and static methods
+ * the instance variables engine and displacement are distinct for 
+ * each and every object whereas static/class variable numberOfCars
+ * is unique and is shared across all objects of this class.
+ * 
+ * @author baeldung
+ *
+ */
+public class Car {
+    private String name;
+    private String engine;
+    
+    public static int numberOfCars;
+    
+    public Car(String name, String engine) {
+        this.name = name;
+        this.engine = engine;
+        numberOfCars++;
+    }
+
+    //getters and setters
+    public static int getNumberOfCars() {
+        return numberOfCars;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getEngine() {
+        return engine;
+    }
+
+    public void setEngine(String engine) {
+        this.engine = engine;
+    }
+
+    public static void setNumberOfCars(int numberOfCars) {
+        Car.numberOfCars = numberOfCars;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/staticdemo/Singleton.java

@@ -0,0 +1,13 @@
+package com.baeldung.staticdemo;
+
+public class Singleton  {    
+    private Singleton() {}
+    
+    private static class SingletonHolder {    
+        public static final Singleton instance = new Singleton();
+    }    
+
+    public static Singleton getInstance() {    
+        return SingletonHolder.instance;    
+    }    
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/staticdemo/StaticBlock.java

@@ -0,0 +1,28 @@
+package com.baeldung.staticdemo;
+
+import java.util.LinkedList;
+import java.util.List;
+
+public class StaticBlock {
+    private static List<String> ranks = new LinkedList<>();
+
+    static {
+        ranks.add("Lieutenant");
+        ranks.add("Captain");
+        ranks.add("Major");
+    }
+    
+    static {
+        ranks.add("Colonel");
+        ranks.add("General");
+    }
+
+    //getters and setters
+    public static List<String> getRanks() {
+        return ranks;
+    }
+
+    public static void setRanks(List<String> ranks) {
+        StaticBlock.ranks = ranks;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/typeerasure/ArrayContentPrintUtil.java

@@ -0,0 +1,16 @@
+package com.baeldung.typeerasure;
+
+public class ArrayContentPrintUtil {
+
+   public static <E> void printArray(E[] array) {
+        for (E element : array) {
+            System.out.printf("%s ", element);
+        }
+    }
+    
+    public static <E extends Comparable<E>> void printArray(E[] array) {
+        for (E element : array) {
+            System.out.printf("%s ", element);
+        }
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/typeerasure/BoundStack.java

@@ -0,0 +1,37 @@
+package com.baeldung.typeerasure;
+
+import java.util.Arrays;
+
+public class BoundStack<E extends Comparable<E>> {
+
+    private E[] stackContent;
+    private int total;
+
+    public BoundStack(int capacity) {
+        this.stackContent = (E[]) new Object[capacity];
+    }
+
+    public void push(E data) {
+        if (total == stackContent.length) {
+            resize(2 * stackContent.length);
+        }
+        stackContent[total++] = data;
+    }
+
+    public E pop() {
+        if (!isEmpty()) {
+            E datum = stackContent[total];
+            stackContent[total--] = null;
+            return datum;
+        }
+        return null;
+    }
+
+    private void resize(int capacity) {
+        Arrays.copyOf(stackContent, capacity);
+    }
+
+    public boolean isEmpty() {
+        return total == 0;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/typeerasure/IntegerStack.java

@@ -0,0 +1,13 @@
+package com.baeldung.typeerasure;
+
+public class IntegerStack extends Stack<Integer> {
+
+    public IntegerStack(int capacity) {
+        super(capacity);
+    }
+
+    public void push(Integer value) {
+        System.out.println("Pushing into my integerStack");
+        super.push(value);
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/typeerasure/Stack.java

@@ -0,0 +1,39 @@
+package com.baeldung.typeerasure;
+
+import java.util.Arrays;
+
+public class Stack<E> {
+
+    private E[] stackContent;
+    private int total;
+
+    public Stack(int capacity) {
+        this.stackContent = (E[]) new Object[capacity];
+    }
+
+    public void push(E data) {
+        System.out.println("In base stack push#");
+        if (total == stackContent.length) {
+            resize(2 * stackContent.length);
+        }
+        stackContent[total++] = data;
+    }
+
+    public E pop() {
+        if (!isEmpty()) {
+            E datum = stackContent[total];
+            stackContent[total--] = null;
+            return datum;
+        }
+        return null;
+    }
+
+    private void resize(int capacity) {
+        Arrays.copyOf(stackContent, capacity);
+    }
+
+    public boolean isEmpty() {
+        return total == 0;
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/resources/logback.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <logger name="org.springframework" level="WARN" />
+    <logger name="org.springframework.transaction" level="WARN" />
+
+    <!-- in order to debug some marshalling issues, this needs to be TRACE -->
+    <logger name="org.springframework.web.servlet.mvc" level="WARN" />
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/casting/CastingUnitTest.java

@@ -0,0 +1,80 @@
+package com.baeldung.casting;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import java.util.ArrayList;
+import java.util.List;
+
+public class CastingUnitTest {
+
+    @Test
+    public void whenPrimitiveConverted_thenValueChanged() {
+        double myDouble = 1.1;
+        int myInt = (int) myDouble;
+
+        assertNotEquals(myDouble, myInt);
+    }
+
+    @Test
+    public void whenUpcast_thenInstanceUnchanged() {
+        Cat cat = new Cat();
+        Animal animal = cat;
+        animal = (Animal) cat;
+        assertTrue(animal instanceof Cat);
+    }
+
+    @Test
+    public void whenUpcastToObject_thenInstanceUnchanged() {
+        Object object = new Animal();
+        assertTrue(object instanceof Animal);
+    }
+
+    @Test
+    public void whenUpcastToInterface_thenInstanceUnchanged() {
+        Mew mew = new Cat();
+        assertTrue(mew instanceof Cat);
+    }
+
+    @Test
+    public void whenUpcastToAnimal_thenOverridenMethodsCalled() {
+        List<Animal> animals = new ArrayList<>();
+        animals.add(new Cat());
+        animals.add(new Dog());
+        new AnimalFeeder().feed(animals);
+    }
+
+    @Test
+    public void whenDowncastToCat_thenMeowIsCalled() {
+        Animal animal = new Cat();
+        ((Cat) animal).meow();
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void whenDownCastWithoutCheck_thenExceptionThrown() {
+        List<Animal> animals = new ArrayList<>();
+        animals.add(new Cat());
+        animals.add(new Dog());
+        new AnimalFeeder().uncheckedFeed(animals);
+    }
+
+    @Test
+    public void whenDowncastToCatWithCastMethod_thenMeowIsCalled() {
+        Animal animal = new Cat();
+        if (Cat.class.isInstance(animal)) {
+            Cat cat = Cat.class.cast(animal);
+            cat.meow();
+        }
+    }
+    
+    @Test
+    public void whenParameterCat_thenOnlyCatsFed() {
+        List<Animal> animals = new ArrayList<>();
+        animals.add(new Cat());
+        animals.add(new Dog());
+        AnimalFeederGeneric<Cat> catFeeder = new AnimalFeederGeneric<Cat>(Cat.class);
+        List<Cat> fedAnimals = catFeeder.feed(animals);
+
+        assertTrue(fedAnimals.size() == 1);
+        assertTrue(fedAnimals.get(0) instanceof Cat);
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/deepcopy/DeepCopyUnitTest.java

@@ -0,0 +1,137 @@
+package com.baeldung.deepcopy;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+
+import org.apache.commons.lang3.SerializationUtils;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.gson.Gson;
+
+public class DeepCopyUnitTest {
+
+    @Test
+    public void whenCreatingDeepCopyWithCopyConstructor_thenObjectsShouldNotBeSame() {
+
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+
+        User deepCopy = new User(pm);
+
+        assertThat(deepCopy).isNotSameAs(pm);
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenCopyShouldNotChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User deepCopy = new User(pm);
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenCloneCopyShouldNotChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User deepCopy = (User) pm.clone();
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenCommonsCloneShouldNotChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User deepCopy = (User) SerializationUtils.clone(pm);
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenGsonCloneShouldNotChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        Gson gson = new Gson();
+        User deepCopy = gson.fromJson(gson.toJson(pm), User.class);
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenJacksonCopyShouldNotChange() throws IOException {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        ObjectMapper objectMapper = new ObjectMapper();
+        User deepCopy = objectMapper.readValue(objectMapper.writeValueAsString(pm), User.class);
+
+        address.setCountry("Great Britain");
+
+        assertThat(deepCopy.getAddress().getCountry()).isNotEqualTo(pm.getAddress().getCountry());
+    }
+
+    @Test
+    @Ignore
+    public void whenMakingCopies_thenShowHowLongEachMethodTakes() throws CloneNotSupportedException, IOException {
+        int times = 1000000;
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+
+        long start = System.currentTimeMillis();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = (User) SerializationUtils.clone(pm);
+        }
+        long end = System.currentTimeMillis();
+        System.out.println("Cloning with Apache Commons Lang took " + (end - start) + " milliseconds.");
+
+        start = System.currentTimeMillis();
+        Gson gson = new Gson();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = gson.fromJson(gson.toJson(pm), User.class);
+        }
+        end = System.currentTimeMillis();
+        System.out.println("Cloning with Gson took " + (end - start) + " milliseconds.");
+
+        start = System.currentTimeMillis();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = new User(pm);
+        }
+        end = System.currentTimeMillis();
+        System.out.println("Cloning with the copy constructor took " + (end - start) + " milliseconds.");
+
+        start = System.currentTimeMillis();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = (User) pm.clone();
+        }
+        end = System.currentTimeMillis();
+        System.out.println("Cloning with Cloneable interface took " + (end - start) + " milliseconds.");
+
+        start = System.currentTimeMillis();
+        ObjectMapper objectMapper = new ObjectMapper();
+        for (int i = 0; i < times; i++) {
+            User primeMinisterClone = objectMapper.readValue(objectMapper.writeValueAsString(pm), User.class);
+        }
+        end = System.currentTimeMillis();
+        System.out.println("Cloning with Jackson took " + (end - start) + " milliseconds.");
+    }
+    
+    @Test
+    public void whenModifyingOriginalObject_ThenCopyShouldChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User shallowCopy = new User(pm.getFirstName(), pm.getLastName(), pm.getAddress());
+        address.setCountry("Great Britain");
+        assertThat(shallowCopy.getAddress().getCountry()).isEqualTo(pm.getAddress().getCountry());
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/deepcopy/ShallowCopyUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.deepcopy;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class ShallowCopyUnitTest {
+
+
+    @Test
+    public void whenShallowCopying_thenObjectsShouldNotBeSame() {
+
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+
+        User shallowCopy = new User(pm.getFirstName(), pm.getLastName(), pm.getAddress());
+
+        assertThat(shallowCopy)
+                .isNotSameAs(pm);
+    }
+
+    @Test
+    public void whenModifyingOriginalObject_thenCopyShouldChange() {
+        Address address = new Address("Downing St 10", "London", "England");
+        User pm = new User("Prime", "Minister", address);
+        User shallowCopy = new User(pm.getFirstName(), pm.getLastName(), pm.getAddress());
+
+        address.setCountry("Great Britain");
+        
+        assertThat(shallowCopy.getAddress().getCountry())
+                .isEqualTo(pm.getAddress().getCountry());
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/finalkeyword/FinalUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.finalkeyword;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class FinalUnitTest {
+
+    @Test
+    public void whenChangedFinalClassProperties_thenChanged() {
+        Cat cat = new Cat();
+        cat.setWeight(1);
+
+        assertEquals(1, cat.getWeight());
+
+    }
+
+    @Test
+    public void whenFinalVariableAssign_thenOnlyOnce() {
+        final int i;
+        i = 1;
+        // i=2;
+    }
+
+    @Test
+    public void whenChangedFinalReference_thenChanged() {
+
+        final Cat cat = new Cat();
+        // cat=new Cat();
+        cat.setWeight(5);
+
+        assertEquals(5, cat.getWeight());
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/hashcode/application/ApplicationUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.hashcode.application;
+
+import com.baeldung.hashcode.entities.User;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.Assert.assertTrue;
+
+public class ApplicationUnitTest {
+
+    @Test
+    public void main_NoInputState_TextPrintedToConsole() throws Exception {
+        Map<User, User> users = new HashMap<>();
+        User user1 = new User(1L, "John", "john@domain.com");
+        User user2 = new User(2L, "Jennifer", "jennifer@domain.com");
+        User user3 = new User(3L, "Mary", "mary@domain.com");
+
+        users.put(user1, user1);
+        users.put(user2, user2);
+        users.put(user3, user3);
+
+        assertTrue(users.containsKey(user1));
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/hashcode/entities/UserUnitTest.java

@@ -0,0 +1,34 @@
+package com.baeldung.hashcode.entities;
+
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+public class UserUnitTest {
+
+    private User user;
+    private User comparisonUser;
+
+    @Before
+    public void setUpUserInstances() {
+        this.user = new User(1L, "test", "test@domain.com");
+        this.comparisonUser = this.user;
+    }
+
+    @After
+    public void tearDownUserInstances() {
+        user = null;
+        comparisonUser = null;
+    }
+
+    @Test
+    public void equals_EqualUserInstance_TrueAssertion() {
+        Assert.assertTrue(user.equals(comparisonUser));
+    }
+
+    @Test
+    public void hashCode_UserHash_TrueAssertion() {
+        Assert.assertEquals(1792276941, user.hashCode());
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/inheritance/AppUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.inheritance;
+
+import com.baeldung.inheritance.*;
+
+import junit.framework.Test;
+import junit.framework.TestCase;
+import junit.framework.TestSuite;
+
+public class AppUnitTest extends TestCase {
+    
+	public AppUnitTest(String testName) {
+        super( testName );
+    }
+
+    public static Test suite() {
+        return new TestSuite(AppUnitTest.class);
+    }
+
+    @SuppressWarnings("static-access")
+	public void testStaticMethodUsingBaseClassVariable() {
+    	Car first = new ArmoredCar();
+    	assertEquals("Car", first.msg());
+    }
+    	
+    @SuppressWarnings("static-access")
+	public void testStaticMethodUsingDerivedClassVariable() {
+    	ArmoredCar second = new ArmoredCar();
+    	assertEquals("ArmoredCar", second.msg());
+    }
+    
+    public void testAssignArmoredCarToCar() {
+    	Employee e1 = new Employee("Shreya", new ArmoredCar());
+    	assertNotNull(e1.getCar());
+    }
+
+    public void testAssignSpaceCarToCar() {
+    	Employee e2 = new Employee("Paul", new SpaceCar());
+    	assertNotNull(e2.getCar());
+    }
+
+    public void testBMWToCar() {
+    	Employee e3 = new Employee("Pavni", new BMW());
+    	assertNotNull(e3.getCar());
+    }
+
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/initializationguide/UserUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.initializationguide;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.lang.reflect.InvocationTargetException;
+
+public class UserUnitTest {
+
+    @Test
+    public void givenUserInstance_whenIntializedWithNew_thenInstanceIsNotNull() {
+        User user = new User("Alice", 1);
+        assertThat(user).isNotNull();
+    }
+
+    @Test
+    public void givenUserInstance_whenInitializedWithReflection_thenInstanceIsNotNull() throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, NoSuchMethodException, SecurityException {
+        User user = User.class.getConstructor(String.class, int.class)
+            .newInstance("Alice", 2);
+        assertThat(user).isNotNull();
+    }
+
+    @Test
+    public void givenUserInstance_whenCopiedWithClone_thenExactMatchIsCreated() throws CloneNotSupportedException {
+        User user = new User("Alice", 3);
+        User clonedUser = (User) user.clone();
+        assertThat(clonedUser).isEqualTo(user);
+    }
+
+    @Test
+    public void givenUserInstance_whenValuesAreNotInitialized_thenUserNameAndIdReturnDefault() {
+        User user = new User();
+        assertThat(user.getName()).isNull();
+        assertThat(user.getId() == 0);
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/methodoverloadingoverriding/test/MethodOverloadingUnitTest.java

@@ -0,0 +1,41 @@
+package com.baeldung.methodoverloadingoverriding.test;
+
+import com.baeldung.methodoverloadingoverriding.util.Multiplier;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+
+public class MethodOverloadingUnitTest {
+    
+    private static Multiplier multiplier;
+    
+    @BeforeClass
+    public static void setUpMultiplierInstance() {
+        multiplier = new Multiplier();
+    }
+ 
+    @Test
+    public void givenMultiplierInstance_whenCalledMultiplyWithTwoIntegers_thenOneAssertion() {
+        assertThat(multiplier.multiply(10, 10)).isEqualTo(100);
+    }
+    
+    @Test
+    public void givenMultiplierInstance_whenCalledMultiplyWithTreeIntegers_thenOneAssertion() {
+        assertThat(multiplier.multiply(10, 10, 10)).isEqualTo(1000);
+    }
+    
+    @Test
+    public void givenMultiplierInstance_whenCalledMultiplyWithIntDouble_thenOneAssertion() {
+        assertThat(multiplier.multiply(10, 10.5)).isEqualTo(105.0);
+    }
+    
+    @Test
+    public void givenMultiplierInstance_whenCalledMultiplyWithDoubleDouble_thenOneAssertion() {
+        assertThat(multiplier.multiply(10.5, 10.5)).isEqualTo(110.25);
+    }
+    
+    @Test
+    public void givenMultiplierInstance_whenCalledMultiplyWithIntIntAndMatching_thenNoTypePromotion() {
+        assertThat(multiplier.multiply(10, 10)).isEqualTo(100);
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/methodoverloadingoverriding/test/MethodOverridingUnitTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.methodoverloadingoverriding.test;
+
+import com.baeldung.methodoverloadingoverriding.model.Car;
+import com.baeldung.methodoverloadingoverriding.model.Vehicle;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+
+public class MethodOverridingUnitTest {
+    
+    private static Vehicle vehicle;
+    private static Car car;
+    
+    @BeforeClass
+    public static void setUpVehicleInstance() {
+        vehicle = new Vehicle();
+    }
+    
+    @BeforeClass
+    public static void setUpCarInstance() {
+        car = new Car();
+    }
+    
+    @Test
+    public void givenVehicleInstance_whenCalledAccelerate_thenOneAssertion() {
+        assertThat(vehicle.accelerate(100)).isEqualTo("The vehicle accelerates at : 100 MPH.");
+    }
+    
+    @Test
+    public void givenVehicleInstance_whenCalledRun_thenOneAssertion() {
+        assertThat(vehicle.run()).isEqualTo("The vehicle is running.");
+    }
+    
+    @Test
+    public void givenVehicleInstance_whenCalledStop_thenOneAssertion() {
+        assertThat(vehicle.stop()).isEqualTo("The vehicle has stopped.");
+    }
+    
+    @Test
+    public void givenCarInstance_whenCalledAccelerate_thenOneAssertion() {
+        assertThat(car.accelerate(80)).isEqualTo("The car accelerates at : 80 MPH.");
+    }
+    
+    @Test
+    public void givenCarInstance_whenCalledRun_thenOneAssertion() {
+        assertThat(car.run()).isEqualTo("The vehicle is running.");
+    }
+    
+    @Test
+    public void givenCarInstance_whenCalledStop_thenOneAssertion() {
+        assertThat(car.stop()).isEqualTo("The vehicle has stopped.");
+    }
+    
+    @Test
+    public void givenVehicleCarInstances_whenCalledAccelerateWithSameArgument_thenNotEqual() {
+        assertThat(vehicle.accelerate(100)).isNotEqualTo(car.accelerate(100));
+    }
+    
+    @Test
+    public void givenVehicleCarInstances_whenCalledRun_thenEqual() {
+        assertThat(vehicle.run()).isEqualTo(car.run());
+    }
+    
+    @Test
+    public void givenVehicleCarInstances_whenCalledStop_thenEqual() {
+        assertThat(vehicle.stop()).isEqualTo(car.stop());
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/polymorphism/PolymorphismUnitTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.polymorphism;
+
+import static org.junit.Assert.*;
+
+import java.awt.image.BufferedImage;
+import org.junit.Test;
+
+public class PolymorphismUnitTest {
+
+    @Test
+    public void givenImageFile_whenFileCreated_shouldSucceed() {
+        ImageFile imageFile = FileManager.createImageFile("SampleImageFile", 200, 100, new BufferedImage(100, 200, BufferedImage.TYPE_INT_RGB).toString()
+            .getBytes(), "v1.0.0");
+        assertEquals(200, imageFile.getHeight());
+    }
+
+    // Downcasting then Upcasting
+    @Test
+    public void givenTextFile_whenTextFileCreatedAndAssignedToGenericFileAndCastBackToTextFileOnGetWordCount_shouldSucceed() {
+        GenericFile textFile = FileManager.createTextFile("SampleTextFile", "This is a sample text content", "v1.0.0");
+        TextFile textFile2 = (TextFile) textFile;
+        assertEquals(6, textFile2.getWordCount());
+    }
+
+    // Downcasting
+    @Test(expected = ClassCastException.class)
+    public void givenGenericFile_whenCastToTextFileAndInvokeGetWordCount_shouldFail() {
+        GenericFile genericFile = new GenericFile();
+        TextFile textFile = (TextFile) genericFile;
+        System.out.println(textFile.getWordCount());
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/staticdemo/CarIntegrationTest.java

@@ -0,0 +1,14 @@
+package com.baeldung.staticdemo;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class CarIntegrationTest {
+    @Test
+    public void whenNumberOfCarObjectsInitialized_thenStaticCounterIncreases() {
+        new Car("Jaguar", "V8");
+        new Car("Bugatti", "W16");
+        assertEquals(2, Car.numberOfCars);
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/staticdemo/SingletonIntegrationTest.java

@@ -0,0 +1,15 @@
+package com.baeldung.staticdemo;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SingletonIntegrationTest {
+
+    @Test
+    public void givenStaticInnerClass_whenMultipleTimesInstanceCalled_thenOnlyOneTimeInitialized() {
+        Singleton object1 = Singleton.getInstance();
+        Singleton object2 = Singleton.getInstance();
+        
+        Assert.assertSame(object1, object2);
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/staticdemo/StaticBlockIntegrationTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.staticdemo;
+
+import static org.hamcrest.collection.IsIterableContainingInOrder.contains;
+import static org.junit.Assert.assertThat;
+
+import java.util.List;
+
+import org.junit.Test;
+
+public class StaticBlockIntegrationTest {
+
+    @Test
+    public void whenAddedListElementsThroughStaticBlock_thenEnsureCorrectOrder() {
+        List<String> actualList = StaticBlock.getRanks();
+        assertThat(actualList, contains("Lieutenant", "Captain", "Major", "Colonel", "General"));
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/typeerasure/TypeErasureUnitTest.java

@@ -0,0 +1,21 @@
+package com.baeldung.typeerasure;
+
+import org.junit.Test;
+
+public class TypeErasureUnitTest {
+
+    @Test(expected = ClassCastException.class)
+    public void givenIntegerStack_whenStringPushedAndAssignPoppedValueToInteger_shouldFail() {
+        IntegerStack integerStack = new IntegerStack(5);
+        Stack stack = integerStack;
+        stack.push("Hello");
+        Integer data = integerStack.pop();
+    }
+
+    @Test
+    public void givenAnyArray_whenInvokedPrintArray_shouldSucceed() {
+        Integer[] scores = new Integer[] { 100, 200, 10, 99, 20 };
+        ArrayContentPrintUtil.printArray(scores);
+    }
+
+}

core-java-modules/core-java-lang-oop/src/test/resources/.gitignore

@@ -0,0 +1,13 @@
+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear