New unit test format

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

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+=========
+
+## Core Java Lang OOP Cookbooks and Examples
+
+### Relevant Articles: 
+- [Guide to hashCode() in Java](http://www.baeldung.com/java-hashcode)
+- [A Guide to the Static Keyword in Java](http://www.baeldung.com/java-static)
+- [Polymorphism in Java](http://www.baeldung.com/java-polymorphism)
+- [Method Overloading and Overriding in Java](http://www.baeldung.com/java-method-overload-override)
+- [How to Make a Deep Copy of an Object in Java](http://www.baeldung.com/java-deep-copy)
+- [Guide to Inheritance in Java](http://www.baeldung.com/java-inheritance)
+- [Object Type Casting in Java](http://www.baeldung.com/java-type-casting)
+- [The “final” Keyword in Java](http://www.baeldung.com/java-final)
+- [Type Erasure in Java Explained](http://www.baeldung.com/java-type-erasure)
+- [Pass-By-Value as a Parameter Passing Mechanism in Java](http://www.baeldung.com/java-pass-by-value-or-pass-by-reference)
+- [Variable and Method Hiding in Java](http://www.baeldung.com/java-variable-method-hiding)
+- [Access Modifiers in Java](http://www.baeldung.com/java-access-modifiers)
+- [Guide to the super Java Keyword](http://www.baeldung.com/java-super)
+- [Guide to the this Java Keyword](http://www.baeldung.com/java-this)
+- [Immutable Objects in Java](http://www.baeldung.com/java-immutable-object)
+- [Inheritance and Composition (Is-a vs Has-a relationship) in Java](http://www.baeldung.com/java-inheritance-composition)
+- [A Guide to Constructors in Java](https://www.baeldung.com/java-constructors)
+- [Java equals() and hashCode() Contracts](https://www.baeldung.com/java-equals-hashcode-contracts)
+- [Marker Interfaces in Java](https://www.baeldung.com/java-marker-interfaces)

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

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+<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>
+    <groupId>com.baeldung</groupId>
+    <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>${gson.version}</version>
+        </dependency>
+        <!-- logging -->
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>${log4j.version}</version>
+        </dependency>
+        <dependency> <!-- needed to bridge to slf4j for projects that use the log4j APIs directly -->
+            <groupId>org.slf4j</groupId>
+            <artifactId>log4j-over-slf4j</artifactId>
+            <version>${org.slf4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>nl.jqno.equalsverifier</groupId>
+            <artifactId>equalsverifier</artifactId>
+            <version>${equalsverifier.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>
+        <equalsverifier.version>3.0.3</equalsverifier.version>
+    </properties>
+
+</project>

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/accessmodifiers/Public.java

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+package com.baeldung.accessmodifiers;
+
+public class Public {
+    public Public() {
+        SuperPublic.publicMethod(); // Available everywhere.
+        SuperPublic.protectedMethod(); // Available in the same package or subclass.
+        SuperPublic.defaultMethod(); // Available in the same package.
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/accessmodifiers/SubClass.java

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+package com.baeldung.accessmodifiers;
+
+public class SubClass extends SuperPublic {
+    public SubClass() {
+        SuperPublic.publicMethod(); // Available everywhere.
+        SuperPublic.protectedMethod(); // Available in the same package or subclass.
+        SuperPublic.defaultMethod(); // Available in the same package.
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/accessmodifiers/SuperPublic.java

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+package com.baeldung.accessmodifiers;
+
+//Only public or default access modifiers are permitted
+public class SuperPublic {
+    // Always available from anywhere
+    static public void publicMethod() {
+        System.out.println(SuperPublic.class.getName() + " publicMethod()");
+    }
+    
+    // Available within the same package
+    static void defaultMethod() {
+        System.out.println(SuperPublic.class.getName() + " defaultMethod()");
+    }
+    
+    // Available within the same package and subclasses
+    static protected void protectedMethod() {
+        System.out.println(SuperPublic.class.getName() + " protectedMethod()");
+    }
+    
+    // Available within the same class only
+    static private void privateMethod() {
+        System.out.println(SuperPublic.class.getName() + " privateMethod()");
+    }
+    
+    // Method in the same class = has access to all members within the same class
+    private void anotherPrivateMethod() {
+        privateMethod();
+        defaultMethod();
+        protectedMethod();
+        publicMethod(); // Available in the same class only.
+    }
+}
+
+// Only public or default access modifiers are permitted
+class SuperDefault {
+    public void publicMethod() {
+        System.out.println(this.getClass().getName() + " publicMethod()");
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/accessmodifiers/another/AnotherPublic.java

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+package com.baeldung.accessmodifiers.another;
+
+import com.baeldung.accessmodifiers.SuperPublic;
+
+public class AnotherPublic {
+    public AnotherPublic() {
+        SuperPublic.publicMethod(); // Available everywhere.
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/accessmodifiers/another/AnotherSubClass.java

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+package com.baeldung.accessmodifiers.another;
+
+import com.baeldung.accessmodifiers.SuperPublic;
+
+public class AnotherSubClass extends SuperPublic {
+    public AnotherSubClass() {
+        SuperPublic.publicMethod(); // Available everywhere.
+        SuperPublic.protectedMethod(); // Available in subclass. Let's note different package.
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/accessmodifiers/another/AnotherSuperPublic.java

@@ -0,0 +1,9 @@
+package com.baeldung.accessmodifiers.another;
+
+import com.baeldung.accessmodifiers.SuperPublic;
+
+public class AnotherSuperPublic {
+    public AnotherSuperPublic() {
+        SuperPublic.publicMethod(); // Available everywhere. Let's note different package.
+    }
+}

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

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+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

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+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/constructors/BankAccount.java

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+package com.baeldung.constructors;
+
+import java.time.LocalDateTime;
+
+class BankAccount {
+    String name;
+    LocalDateTime opened;
+    double balance;
+    
+    @Override
+    public String toString() {
+        return String.format("%s, %s, %f", this.name, this.opened.toString(), this.balance);
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public LocalDateTime getOpened() {
+        return opened;
+    }
+
+    public double getBalance() {
+        return this.balance;
+    }
+}
+
+class BankAccountEmptyConstructor extends BankAccount {
+    public BankAccountEmptyConstructor() {
+        this.name = "";
+        this.opened = LocalDateTime.now();
+        this.balance = 0.0d;
+    }
+}
+
+class BankAccountParameterizedConstructor extends BankAccount {
+    public BankAccountParameterizedConstructor(String name, LocalDateTime opened, double balance) {
+        this.name = name;
+        this.opened = opened;
+        this.balance = balance;
+    }
+}
+
+class BankAccountCopyConstructor extends BankAccount {
+    public BankAccountCopyConstructor(String name, LocalDateTime opened, double balance) {
+        this.name = name;
+        this.opened = opened;
+        this.balance = balance;
+    }
+        
+    public BankAccountCopyConstructor(BankAccount other) {
+        this.name = other.name;
+        this.opened = LocalDateTime.now();
+        this.balance = 0.0f;
+    }
+}
+
+class BankAccountChainedConstructors extends BankAccount {
+    public BankAccountChainedConstructors(String name, LocalDateTime opened, double balance) {
+        this.name = name;
+        this.opened = opened;
+        this.balance = balance;
+    }
+
+    public BankAccountChainedConstructors(String name) {
+        this(name, LocalDateTime.now(), 0.0f);
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/constructors/Transaction.java

@@ -0,0 +1,25 @@
+package com.baeldung.constructors;
+
+import java.time.LocalDateTime;
+
+class Transaction {
+    final BankAccountEmptyConstructor bankAccount;
+    final LocalDateTime date;
+    final double amount;
+
+    public Transaction(BankAccountEmptyConstructor account, LocalDateTime date, double amount) {
+        this.bankAccount = account;
+        this.date = date;
+        this.amount = amount;
+    }
+
+    /*
+     * Compilation Error :'(, all final variables must be explicitly initialised.
+     * public Transaction() {
+     * }
+     */
+
+    public void invalidMethod() {
+        // this.amount = 102.03; // Results in a compiler error. You cannot change the value of a final variable.
+    }    
+}

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

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+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/equalshashcode/Money.java

@@ -0,0 +1,36 @@
+package com.baeldung.equalshashcode;
+
+class Money {
+
+    int amount;
+    String currencyCode;
+
+    Money(int amount, String currencyCode) {
+        this.amount = amount;
+        this.currencyCode = currencyCode;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == this)
+            return true;
+        if (!(o instanceof Money))
+            return false;
+        Money other = (Money)o;
+        boolean currencyCodeEquals = (this.currencyCode == null && other.currencyCode == null)
+          || (this.currencyCode != null && this.currencyCode.equals(other.currencyCode));
+        return this.amount == other.amount
+          && currencyCodeEquals;
+    }
+
+    @Override
+    public int hashCode() {
+        int result = 17;
+        result = 31 * result + amount;
+        if (currencyCode != null) {
+            result = 31 * result + currencyCode.hashCode();
+        }
+        return result;
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/Team.java

@@ -0,0 +1,39 @@
+package com.baeldung.equalshashcode;
+
+class Team {
+
+    final String city;
+    final String department;
+
+    Team(String city, String department) {
+        this.city = city;
+        this.department = department;
+    }
+
+    @Override
+    public final boolean equals(Object o) {
+        if (o == this)
+            return true;
+        if (!(o instanceof Team))
+            return false;
+        Team otherTeam = (Team)o;
+        boolean cityEquals = (this.city == null && otherTeam.city == null)
+          || this.city != null && this.city.equals(otherTeam.city);
+        boolean departmentEquals = (this.department == null && otherTeam.department == null)
+          || this.department != null && this.department.equals(otherTeam.department);
+        return cityEquals && departmentEquals;
+    }
+
+    @Override
+    public final int hashCode() {
+        int result = 17;
+        if (city != null) {
+            result = 31 * result + city.hashCode();
+        }
+        if (department != null) {
+            result = 31 * result + department.hashCode();
+        }
+        return result;
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/Voucher.java

@@ -0,0 +1,38 @@
+package com.baeldung.equalshashcode;
+
+class Voucher {
+
+    private Money value;
+    private String store;
+
+    Voucher(int amount, String currencyCode, String store) {
+        this.value = new Money(amount, currencyCode);
+        this.store = store;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == this)
+            return true;
+        if (!(o instanceof Voucher))
+            return false;
+        Voucher other = (Voucher)o;
+        boolean valueEquals = (this.value == null && other.value == null)
+          || (this.value != null && this.value.equals(other.value));
+        boolean storeEquals = (this.store == null && other.store == null)
+          || (this.store != null && this.store.equals(other.store));
+        return valueEquals && storeEquals;
+    }
+
+    @Override
+    public int hashCode() {
+        int result = 17;
+        if (this.value != null) {
+            result = 31 * result + value.hashCode();
+        }
+        if (this.store != null) {
+            result = 31 * result + store.hashCode();
+        }
+        return result;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/WrongTeam.java

@@ -0,0 +1,30 @@
+package com.baeldung.equalshashcode;
+
+/* (non-Javadoc)
+* This class overrides equals, but it doesn't override hashCode.
+*
+* To see which problems this leads to:
+* TeamUnitTest.givenMapKeyWithoutHashCode_whenSearched_thenReturnsWrongValue
+*/
+class WrongTeam {
+
+    String city;
+    String department;
+
+    WrongTeam(String city, String department) {
+        this.city = city;
+        this.department = department;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == this)
+            return true;
+        if (!(o instanceof WrongTeam))
+            return false;
+        WrongTeam otherTeam = (WrongTeam)o;
+        return this.city == otherTeam.city
+          && this.department == otherTeam.department;
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/WrongVoucher.java

@@ -0,0 +1,47 @@
+package com.baeldung.equalshashcode;
+
+/* (non-Javadoc)
+* This class extends the Money class that has overridden the equals method and once again overrides the equals method.
+*
+* To see which problems this leads to:
+* MoneyUnitTest.givenMoneyAndVoucherInstances_whenEquals_thenReturnValuesArentSymmetric
+*/
+class WrongVoucher extends Money {
+
+    private String store;
+
+    WrongVoucher(int amount, String currencyCode, String store) {
+        super(amount, currencyCode);
+
+        this.store = store;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == this)
+            return true;
+        if (!(o instanceof WrongVoucher))
+            return false;
+        WrongVoucher other = (WrongVoucher)o;
+        boolean currencyCodeEquals = (this.currencyCode == null && other.currencyCode == null)
+          || (this.currencyCode != null && this.currencyCode.equals(other.currencyCode));
+        boolean storeEquals = (this.store == null && other.store == null)
+          || (this.store != null && this.store.equals(other.store));
+        return this.amount == other.amount
+          && currencyCodeEquals
+          && storeEquals;
+    }
+
+    @Override
+    public int hashCode() {
+        int result = 17;
+        result = 31 * result + amount;
+        if (this.currencyCode != null) {
+            result = 31 * result + currencyCode.hashCode();
+        }
+        if (this.store != null) {
+            result = 31 * result + store.hashCode();
+        }
+        return result;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/entities/ComplexClass.java

@@ -0,0 +1,63 @@
+package com.baeldung.equalshashcode.entities;
+
+import java.util.List;
+import java.util.Set;
+
+public class ComplexClass {
+
+    private List<?> genericList;
+    private Set<Integer> integerSet;
+
+    public ComplexClass(List<?> genericArrayList, Set<Integer> integerHashSet) {
+        super();
+        this.genericList = genericArrayList;
+        this.integerSet = integerHashSet;
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + ((genericList == null) ? 0 : genericList.hashCode());
+        result = prime * result + ((integerSet == null) ? 0 : integerSet.hashCode());
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (!(obj instanceof ComplexClass))
+            return false;
+        ComplexClass other = (ComplexClass) obj;
+        if (genericList == null) {
+            if (other.genericList != null)
+                return false;
+        } else if (!genericList.equals(other.genericList))
+            return false;
+        if (integerSet == null) {
+            if (other.integerSet != null)
+                return false;
+        } else if (!integerSet.equals(other.integerSet))
+            return false;
+        return true;
+    }
+
+    protected List<?> getGenericList() {
+        return genericList;
+    }
+
+    protected void setGenericArrayList(List<?> genericList) {
+        this.genericList = genericList;
+    }
+
+    protected Set<Integer> getIntegerSet() {
+        return integerSet;
+    }
+
+    protected void setIntegerSet(Set<Integer> integerSet) {
+        this.integerSet = integerSet;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/entities/PrimitiveClass.java

@@ -0,0 +1,54 @@
+package com.baeldung.equalshashcode.entities;
+
+public class PrimitiveClass {
+
+    private boolean primitiveBoolean;
+    private int primitiveInt;
+
+    public PrimitiveClass(boolean primitiveBoolean, int primitiveInt) {
+        super();
+        this.primitiveBoolean = primitiveBoolean;
+        this.primitiveInt = primitiveInt;
+    }
+
+    protected boolean isPrimitiveBoolean() {
+        return primitiveBoolean;
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + (primitiveBoolean ? 1231 : 1237);
+        result = prime * result + primitiveInt;
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        PrimitiveClass other = (PrimitiveClass) obj;
+        if (primitiveBoolean != other.primitiveBoolean)
+            return false;
+        if (primitiveInt != other.primitiveInt)
+            return false;
+        return true;
+    }
+
+    protected void setPrimitiveBoolean(boolean primitiveBoolean) {
+        this.primitiveBoolean = primitiveBoolean;
+    }
+
+    protected int getPrimitiveInt() {
+        return primitiveInt;
+    }
+
+    protected void setPrimitiveInt(int primitiveInt) {
+        this.primitiveInt = primitiveInt;
+    }
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/entities/Rectangle.java

@@ -0,0 +1,58 @@
+package com.baeldung.equalshashcode.entities;
+
+public class Rectangle extends Shape {
+    private double width;
+    private double length;
+
+    public Rectangle(double width, double length) {
+        this.width = width;
+        this.length = length;
+    }
+
+    @Override
+    public double area() {
+        return width * length;
+    }
+
+    @Override
+    public double perimeter() {
+        return 2 * (width + length);
+    }
+
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        long temp;
+        temp = Double.doubleToLongBits(length);
+        result = prime * result + (int) (temp ^ (temp >>> 32));
+        temp = Double.doubleToLongBits(width);
+        result = prime * result + (int) (temp ^ (temp >>> 32));
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj)
+            return true;
+        if (obj == null)
+            return false;
+        if (getClass() != obj.getClass())
+            return false;
+        Rectangle other = (Rectangle) obj;
+        if (Double.doubleToLongBits(length) != Double.doubleToLongBits(other.length))
+            return false;
+        if (Double.doubleToLongBits(width) != Double.doubleToLongBits(other.width))
+            return false;
+        return true;
+    }
+
+    protected double getWidth() {
+        return width;
+    }
+
+    protected double getLength() {
+        return length;
+    }
+
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/entities/Shape.java

@@ -0,0 +1,7 @@
+package com.baeldung.equalshashcode.entities;
+
+public abstract class Shape {
+    public abstract double area();
+
+    public abstract double perimeter();
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/equalshashcode/entities/Square.java

@@ -0,0 +1,58 @@
+package com.baeldung.equalshashcode.entities;
+
+import java.awt.*;
+
+public class Square extends Rectangle {
+
+    private Color color;
+
+    public Square(double width, Color color) {
+        super(width, width);
+        this.color = color;
+    }
+
+    /* (non-Javadoc)
+     * @see java.lang.Object#hashCode()
+     */
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = super.hashCode();
+        result = prime * result + ((color == null) ? 0 : color.hashCode());
+        return result;
+    }
+
+    /* (non-Javadoc)
+     * @see java.lang.Object#equals(java.lang.Object)
+     */
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (!super.equals(obj)) {
+            return false;
+        }
+        if (!(obj instanceof Square)) {
+            return false;
+        }
+        Square other = (Square) obj;
+        if (color == null) {
+            if (other.color != null) {
+                return false;
+            }
+        } else if (!color.equals(other.color)) {
+            return false;
+        }
+        return true;
+    }
+
+    protected Color getColor() {
+        return color;
+    }
+
+    protected void setColor(Color color) {
+        this.color = color;
+    }
+
+}

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 {
+
+}