[JAVA-621] core-java-lang-oop-types module

* Creation

* Moved code from https://www.baeldung.com/java-marker-interfaces

* Moved code from https://www.baeldung.com/java-abstract-class

* Moved code from https://www.baeldung.com/java-this

* Moved code from https://www.baeldung.com/java-nested-classes

* Moved code from https://www.baeldung.com/java-inner-interfaces

* Moved code from https://www.baeldung.com/java-classes-objects

* Moved article references to the new README.md

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

@@ -0,0 +1,11 @@
+## Core Java Lang OOP - Types
+
+This module contains articles about types in Java
+
+### Relevant Articles: 
+- [Java Classes and Objects](https://www.baeldung.com/java-classes-objects)
+- [Guide to the this Java Keyword](https://www.baeldung.com/java-this)
+- [Abstract Classes in Java](https://www.baeldung.com/java-abstract-class)
+- [Nested Classes in Java](https://www.baeldung.com/java-nested-classes)
+- [A Guide to Inner Interfaces in Java](https://www.baeldung.com/java-inner-interfaces)
+- [Marker Interfaces in Java](https://www.baeldung.com/java-marker-interfaces)

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

@@ -0,0 +1,28 @@
+<?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">
+    <parent>
+        <artifactId>core-java-lang-oop-modules</artifactId>
+        <groupId>com.baeldung.core-java-lang-oop-modules</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>core-java-lang-oop-types</artifactId>
+    <name>core-java-lang-oop-types</name>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <assertj-core.version>3.10.0</assertj-core.version>
+    </properties>
+</project>

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

@@ -0,0 +1,29 @@
+package com.baeldung.abstractclasses.application;
+
+import com.baeldung.abstractclasses.filereaders.BaseFileReader;
+import com.baeldung.abstractclasses.filereaders.LowercaseFileReader;
+import com.baeldung.abstractclasses.filereaders.UppercaseFileReader;
+import java.io.IOException;
+import java.net.URISyntaxException;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+public class Application {
+
+    public static void main(String[] args) throws IOException, URISyntaxException {
+
+        Application application = new Application();
+        Path path = application.getPathFromResourcesFile("files/test.txt");
+        BaseFileReader lowercaseFileReader = new LowercaseFileReader(path);
+        lowercaseFileReader.readFile().forEach(line -> System.out.println(line));
+        
+        BaseFileReader uppercaseFileReader = new UppercaseFileReader(path);
+        uppercaseFileReader.readFile().forEach(line -> System.out.println(line));
+
+    }
+    
+    private Path getPathFromResourcesFile(String filePath) throws URISyntaxException {
+        return Paths.get(getClass().getClassLoader().getResource(filePath).toURI());
+         
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/abstractclasses/filereaders/BaseFileReader.java

@@ -0,0 +1,27 @@
+package com.baeldung.abstractclasses.filereaders;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public abstract class BaseFileReader {
+    
+    protected Path filePath;
+    
+    protected BaseFileReader(Path filePath) {
+        this.filePath = filePath;
+    }
+    
+    public Path getFilePath() {
+        return filePath;
+    }
+    
+    public List<String> readFile() throws IOException {
+        return Files.lines(filePath)
+            .map(this::mapFileLine).collect(Collectors.toList());
+    }
+    
+    protected abstract String mapFileLine(String line);
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/abstractclasses/filereaders/LowercaseFileReader.java

@@ -0,0 +1,15 @@
+package com.baeldung.abstractclasses.filereaders;
+
+import java.nio.file.Path;
+
+public class LowercaseFileReader extends BaseFileReader {
+
+    public LowercaseFileReader(Path filePath) {
+        super(filePath);
+    }
+
+    @Override
+    public String mapFileLine(String line) {
+        return line.toLowerCase();
+    }   
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/abstractclasses/filereaders/UppercaseFileReader.java

@@ -0,0 +1,15 @@
+package com.baeldung.abstractclasses.filereaders;
+
+import java.nio.file.Path;
+
+public class UppercaseFileReader extends BaseFileReader {
+
+    public UppercaseFileReader(Path filePath) {
+        super(filePath);
+    }
+
+    @Override
+    public String mapFileLine(String line) {
+        return line.toUpperCase();
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/innerinterfaces/CommaSeparatedCustomers.java

@@ -0,0 +1,21 @@
+package com.baeldung.innerinterfaces;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class CommaSeparatedCustomers implements Customer.List {
+
+    private List<Customer> customers = new ArrayList<Customer>();
+
+    @Override
+    public void Add(Customer customer) {
+        customers.add(customer);
+    }
+
+    @Override
+    public String getCustomerNames() {
+        return customers.stream().map(customer -> customer.getName()).collect(Collectors.joining(","));
+    }
+
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/innerinterfaces/Customer.java

@@ -0,0 +1,19 @@
+package com.baeldung.innerinterfaces;
+
+public class Customer {
+    public interface List {
+        void Add(Customer customer);
+
+        String getCustomerNames();
+    }
+
+    private String name;
+
+    public Customer(String name) {
+        this.name = name;
+    }
+
+    String getName() {
+        return name;
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/keyword/thiskeyword/KeywordUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.keyword.thiskeyword;
+
+public class KeywordUnitTest {
+
+    private String name;
+    private int age;
+
+    public KeywordUnitTest() {
+        this("John", 27);
+        this.printMessage();
+        printInstance(this);
+    }
+
+    public KeywordUnitTest(String name, int age) {
+        this.name = name;
+        this.age = age;
+    }
+
+    public void printMessage() {
+        System.out.println("invoked by this");
+    }
+
+    public void printInstance(KeywordUnitTest thisKeyword) {
+        System.out.println(thisKeyword);
+    }
+
+    public KeywordUnitTest getCurrentInstance() {
+        return this;
+    }
+
+    class ThisInnerClass {
+
+        boolean isInnerClass = true;
+
+        public ThisInnerClass() {
+            KeywordUnitTest thisKeyword = KeywordUnitTest.this;
+            String outerString = KeywordUnitTest.this.name;
+            System.out.println(this.isInnerClass);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return "KeywordTest{" +
+                "name='" + name + '\'' +
+                ", age=" + age +
+                '}';
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/markerinterface/DeletableShape.java

@@ -0,0 +1,5 @@
+package com.baeldung.markerinterface;
+
+public interface DeletableShape extends Shape {
+
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/markerinterface/Rectangle.java

@@ -0,0 +1,22 @@
+package com.baeldung.markerinterface;
+
+public class Rectangle implements DeletableShape {
+
+    private double width;
+    private double height;
+
+    public Rectangle(double width, double height) {
+        this.width = width;
+        this.height = height;
+    }
+
+    @Override
+    public double getArea() {
+        return width * height;
+    }
+
+    @Override
+    public double getCircumference() {
+        return 2 * (width + height);
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/markerinterface/Shape.java

@@ -0,0 +1,6 @@
+package com.baeldung.markerinterface;
+
+public interface Shape {
+    double getArea();
+    double getCircumference();
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/java/com/baeldung/markerinterface/ShapeDao.java

@@ -0,0 +1,14 @@
+package com.baeldung.markerinterface;
+
+public class ShapeDao {
+
+    public boolean delete(Object object) {
+        if (!(object instanceof DeletableShape)) {
+            return false;
+        }
+        // Calling the code that deletes the entity from the database
+
+        return true;
+    }
+
+}

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

@@ -0,0 +1,51 @@
+package com.baeldung.objects;
+
+public class Car {
+
+    private String type;
+    private String model;
+    private String color;
+    private int speed;
+
+    public Car(String type, String model, String color) {
+        this.type = type;
+        this.model = model;
+        this.color = color;
+    }
+
+    public String getColor() {
+        return color;
+    }
+
+    public void setColor(String color) {
+        this.color = color;
+    }
+
+    public int getSpeed() {
+        return speed;
+    }
+    
+    public int increaseSpeed(int increment) {
+        if (increment > 0) {
+            this.speed += increment;
+        } else {
+            System.out.println("Increment can't be negative.");
+        }
+        return this.speed;
+    }
+    
+    public int decreaseSpeed(int decrement) {
+        if (decrement > 0 && decrement <= this.speed) {
+            this.speed -= decrement;
+        } else {
+            System.out.println("Decrement can't be negative or greater than current speed.");
+        }
+        return this.speed;
+    }
+
+    @Override
+    public String toString() {
+        return "Car [type=" + type + ", model=" + model + ", color=" + color + ", speed=" + speed + "]";
+    }
+    
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/main/resources/files/test.txt

@@ -0,0 +1,10 @@
+This is line 1
+This is line 2
+This is line 3
+This is line 4
+This is line 5
+This is line 6
+This is line 7
+This is line 8
+This is line 9
+This is line 10

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/abstractclasses/test/LowercaseFileReaderUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.abstractclasses.test;
+
+import com.baeldung.abstractclasses.filereaders.BaseFileReader;
+import com.baeldung.abstractclasses.filereaders.LowercaseFileReader;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class LowercaseFileReaderUnitTest {
+    
+    @Test
+    public void givenLowercaseFileReaderInstance_whenCalledreadFile_thenCorrect() throws Exception {
+        Path path = Paths.get(getClass().getClassLoader().getResource("files/test.txt").toURI());
+        BaseFileReader lowercaseFileReader = new LowercaseFileReader(path);
+        
+        assertThat(lowercaseFileReader.readFile()).isInstanceOf(List.class);
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/abstractclasses/test/UppercaseFileReaderUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.abstractclasses.test;
+
+import com.baeldung.abstractclasses.filereaders.BaseFileReader;
+import com.baeldung.abstractclasses.filereaders.UppercaseFileReader;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class UppercaseFileReaderUnitTest {
+
+    @Test
+    public void givenUppercaseFileReaderInstance_whenCalledreadFile_thenCorrect() throws Exception {
+        Path path = Paths.get(getClass().getClassLoader().getResource("files/test.txt").toURI());
+        BaseFileReader uppercaseFileReader = new UppercaseFileReader(path);
+        
+        assertThat(uppercaseFileReader.readFile()).isInstanceOf(List.class);
+    }    
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/innerinterfaces/InnerInterfaceUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.innerinterfaces;
+
+import com.baeldung.innerinterfaces.CommaSeparatedCustomers;
+import com.baeldung.innerinterfaces.Customer;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(JUnit4.class)
+public class InnerInterfaceUnitTest {
+    @Test
+    public void whenCustomerListJoined_thenReturnsJoinedNames() {
+        Customer.List customerList = new CommaSeparatedCustomers();
+        customerList.Add(new Customer("customer1"));
+        customerList.Add(new Customer("customer2"));
+        assertEquals("customer1,customer2", customerList.getCustomerNames());
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/markerinterface/MarkerInterfaceUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.markerinterface;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class MarkerInterfaceUnitTest {
+
+    @Test
+    public void givenDeletableObjectThenTrueReturned() {
+        ShapeDao shapeDao = new ShapeDao();
+        Object rectangle = new Rectangle(2, 3);
+
+        boolean result = shapeDao.delete(rectangle);
+        assertEquals(true, result);
+    }
+    
+    @Test
+    public void givenNonDeletableObjectThenFalseReturned() {
+        ShapeDao shapeDao = new ShapeDao();
+        Object object = new Object();
+
+        boolean result = shapeDao.delete(object);
+        assertEquals(false, result);
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/AnonymousInner.java

@@ -0,0 +1,20 @@
+package com.baeldung.nestedclass;
+
+import org.junit.Test;
+
+abstract class SimpleAbstractClass {
+    abstract void run();
+}
+
+public class AnonymousInner {
+
+    @Test
+    public void run() {
+        SimpleAbstractClass simpleAbstractClass = new SimpleAbstractClass() {
+            void run() {
+                System.out.println("Running Anonymous Class...");
+            }
+        };
+        simpleAbstractClass.run();
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/Enclosing.java

@@ -0,0 +1,21 @@
+package com.baeldung.nestedclass;
+
+import org.junit.Test;
+
+public class Enclosing {
+
+    private static int x = 1;
+
+    public static class StaticNested {
+
+        private void run() {
+            System.out.println("x = " + x);
+        }
+    }
+
+    @Test
+    public void test() {
+        StaticNested nested = new StaticNested();
+        nested.run();
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/NewEnclosing.java

@@ -0,0 +1,22 @@
+package com.baeldung.nestedclass;
+
+import org.junit.Test;
+
+public class NewEnclosing {
+
+    private void run() {
+        class Local {
+            void run() {
+                System.out.println("Welcome to Baeldung!");
+            }
+        }
+        Local local = new Local();
+        local.run();
+    }
+
+    @Test
+    public void test() {
+        NewEnclosing newEnclosing = new NewEnclosing();
+        newEnclosing.run();
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/NewOuter.java

@@ -0,0 +1,30 @@
+package com.baeldung.nestedclass;
+
+import org.junit.Test;
+
+public class NewOuter {
+
+    int a = 1;
+    static int b = 2;
+
+    public class InnerClass {
+        int a = 3;
+        static final int b = 4;
+
+        public void run() {
+            System.out.println("a = " + a);
+            System.out.println("b = " + b);
+            System.out.println("NewOuter.this.a = " + NewOuter.this.a);
+            System.out.println("NewOuter.b = " + NewOuter.b);
+            System.out.println("NewOuter.this.b = " + NewOuter.this.b);
+        }
+    }
+
+    @Test
+    public void test() {
+        NewOuter outer = new NewOuter();
+        InnerClass inner = outer.new InnerClass();
+        inner.run();
+
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/Outer.java

@@ -0,0 +1,20 @@
+package com.baeldung.nestedclass;
+
+import org.junit.Test;
+
+public class Outer {
+
+    public class Inner {
+
+        public void run() {
+            System.out.println("Calling test...");
+        }
+    }
+
+    @Test
+    public void test() {
+        Outer outer = new Outer();
+        Inner inner = outer.new Inner();
+        inner.run();
+    }
+}

core-java-modules/core-java-lang-oop-modules/core-java-lang-oop-types/src/test/java/com/baeldung/objects/ObjectsUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.objects;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class ObjectsUnitTest {
+    
+    private Car car;
+
+    @Before
+    public void setUp() throws Exception {
+        car = new Car("Ford", "Focus", "red");
+    }
+
+    @Test
+    public final void when_speedIncreased_then_verifySpeed() {
+        car.increaseSpeed(30);
+        assertEquals(30, car.getSpeed());
+        
+        car.increaseSpeed(20);
+        assertEquals(50, car.getSpeed());
+    }
+    
+    @Test
+    public final void when_speedDecreased_then_verifySpeed() {
+        car.increaseSpeed(50);
+        assertEquals(50, car.getSpeed());
+        
+        car.decreaseSpeed(30);
+        assertEquals(20, car.getSpeed());
+        
+        car.decreaseSpeed(20);
+        assertEquals(0, car.getSpeed());
+    }
+
+}

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

@@ -19,5 +19,6 @@
         <module>core-java-lang-oop-patterns</module>
         <module>core-java-lang-oop-generics</module>
         <module>core-java-lang-oop-modifiers</module>
+        <module>core-java-lang-oop-types</module>
     </modules>
 </project>