diff --git a/core-java-modules/core-java-lang-oop-generics/src/main/java/com/baeldung/typeerasure/Example.java b/core-java-modules/core-java-lang-oop-generics/src/main/java/com/baeldung/typeerasure/Example.java
new file mode 100644
index 0000000000..f816fd6d16
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-generics/src/main/java/com/baeldung/typeerasure/Example.java
@@ -0,0 +1,13 @@
+package com.baeldung.typeerasure;
+
+public class Example {
+
+    public static  <E> boolean containsElement(E [] elements, E element){
+        for (E e : elements){
+            if(e.equals(element)){
+                return true;
+            }
+        }
+        return false;
+    }
+}
diff --git a/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/abstractclasses/overview/BoardGame.java b/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/abstractclasses/overview/BoardGame.java
new file mode 100644
index 0000000000..e0395cec7e
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/abstractclasses/overview/BoardGame.java
@@ -0,0 +1,9 @@
+package com.baeldung.abstractclasses.overview;
+
+public abstract class BoardGame {
+    //... field declarations, constructors
+
+    public abstract void play();
+
+    //... concrete methods
+}
diff --git a/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/abstractclasses/overview/Checkers.java b/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/abstractclasses/overview/Checkers.java
new file mode 100644
index 0000000000..5c911649c8
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/abstractclasses/overview/Checkers.java
@@ -0,0 +1,8 @@
+package com.baeldung.abstractclasses.overview;
+
+public class Checkers extends BoardGame {
+    @Override
+    public void play() {
+        //... implementation
+    }
+}
diff --git a/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/interfaces/Computer.java b/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/interfaces/Computer.java
new file mode 100644
index 0000000000..94d39e2448
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/interfaces/Computer.java
@@ -0,0 +1,9 @@
+package com.baeldung.interfaces;
+
+public class Computer implements Electronic {
+
+    @Override
+    public int getElectricityUse() {
+        return 1000;
+    }
+}
diff --git a/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/interfaces/Electronic.java b/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/interfaces/Electronic.java
new file mode 100644
index 0000000000..fcaf67dc3a
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-inheritance/src/main/java/com/baeldung/interfaces/Electronic.java
@@ -0,0 +1,22 @@
+package com.baeldung.interfaces;
+
+public interface Electronic {
+    // Constant variable
+    String LED = "LED";
+
+    // Abstract method
+    int getElectricityUse();
+
+    // Static method
+    static boolean isEnergyEfficient(String electtronicType) {
+        if (electtronicType.equals(LED)) {
+            return true;
+        }
+        return false;
+    }
+
+    //Default method
+    default void printDescription() {
+        System.out.println("Electronic Description");
+    }
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/pom.xml b/core-java-modules/core-java-lang-oop-methods/pom.xml
index 77e8ded8e7..3590b85454 100644
--- a/core-java-modules/core-java-lang-oop-methods/pom.xml
+++ b/core-java-modules/core-java-lang-oop-methods/pom.xml
@@ -14,6 +14,17 @@
     <packaging>jar</packaging>
 
     <dependencies>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>commons-lang</groupId>
+            <artifactId>commons-lang</artifactId>
+            <version>${commons-lang.version}</version>
+        </dependency>
+
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>
@@ -29,6 +40,9 @@
     </dependencies>
 
     <properties>
+        <lombok.version>1.18.12</lombok.version>
+        <commons-lang.version>2.6</commons-lang.version>
+
         <assertj-core.version>3.10.0</assertj-core.version>
         <equalsverifier.version>3.0.3</equalsverifier.version>
     </properties>
diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/apachecommons/User.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/apachecommons/User.java
new file mode 100644
index 0000000000..4be082019a
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/apachecommons/User.java
@@ -0,0 +1,42 @@
+package com.baeldung.hashcode.apachecommons;
+
+import org.apache.commons.lang.builder.HashCodeBuilder;
+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() {
+        return new HashCodeBuilder(17, 37).
+          append(id).
+          append(name).
+          append(email).
+          toHashCode();
+    }
+    // getters and setters here
+    
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/eclipse/User.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/eclipse/User.java
new file mode 100644
index 0000000000..e852eef96e
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/eclipse/User.java
@@ -0,0 +1,42 @@
+package com.baeldung.hashcode.eclipse;
+
+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() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + ((email == null) ? 0 : email.hashCode());
+        result = prime * result + (int) (id ^ (id >>> 32));
+        result = prime * result + ((name == null) ? 0 : name.hashCode());
+        return result;
+    }
+    // getters and setters here
+    
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/improved/User.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/improved/User.java
new file mode 100644
index 0000000000..773a2c7e45
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/improved/User.java
@@ -0,0 +1,37 @@
+package com.baeldung.hashcode.improved;
+
+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() {
+        return (int) id * name.hashCode() * email.hashCode();
+    }
+    // getters and setters here
+    
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/intellij/User.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/intellij/User.java
new file mode 100644
index 0000000000..f7bf1ab735
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/intellij/User.java
@@ -0,0 +1,40 @@
+package com.baeldung.hashcode.intellij;
+
+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 result = (int) (id ^ (id >>> 32));
+        result = 31 * result + name.hashCode();
+        result = 31 * result + email.hashCode();
+        return result;
+    }
+    // getters and setters here
+    
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/lombok/User.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/lombok/User.java
new file mode 100644
index 0000000000..e34246ce24
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/lombok/User.java
@@ -0,0 +1,22 @@
+package com.baeldung.hashcode.lombok;
+
+import lombok.EqualsAndHashCode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+@EqualsAndHashCode
+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;
+    }
+    // getters and setters here
+    
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/naive/User.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/naive/User.java
new file mode 100644
index 0000000000..b0a33ad3e9
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/naive/User.java
@@ -0,0 +1,37 @@
+package com.baeldung.hashcode.naive;
+
+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() {
+        return 1;
+    }
+    // getters and setters here
+    
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/entities/User.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/standard/User.java
similarity index 89%
rename from core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/entities/User.java
rename to core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/standard/User.java
index 524f176e6b..f8fd5cedbd 100644
--- a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/entities/User.java
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/hashcode/standard/User.java
@@ -1,4 +1,4 @@
-package com.baeldung.hashcode.entities;
+package com.baeldung.hashcode.standard;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -34,7 +34,6 @@ public class User {
         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
diff --git a/core-java-modules/core-java-lang-oop-methods/src/test/java/com/baeldung/equalshashcode/TeamUnitTest.java b/core-java-modules/core-java-lang-oop-methods/src/test/java/com/baeldung/equalshashcode/TeamUnitTest.java
index 7dfc6d47a3..308004452b 100644
--- a/core-java-modules/core-java-lang-oop-methods/src/test/java/com/baeldung/equalshashcode/TeamUnitTest.java
+++ b/core-java-modules/core-java-lang-oop-methods/src/test/java/com/baeldung/equalshashcode/TeamUnitTest.java
@@ -38,7 +38,7 @@ public class TeamUnitTest {
     }
 
     @Test
-    public void equalsContract() {
+    public void equalsHashCodeContracts() {
         EqualsVerifier.forClass(Team.class).verify();
     }
 
diff --git a/core-java-modules/core-java-lang-oop-modifiers/src/main/java/com/baeldung/staticmodifier/StaticBlock.java b/core-java-modules/core-java-lang-oop-modifiers/src/main/java/com/baeldung/staticmodifier/StaticBlockDemo.java
similarity index 87%
rename from core-java-modules/core-java-lang-oop-modifiers/src/main/java/com/baeldung/staticmodifier/StaticBlock.java
rename to core-java-modules/core-java-lang-oop-modifiers/src/main/java/com/baeldung/staticmodifier/StaticBlockDemo.java
index f3eb447bdd..637bb5e82a 100644
--- a/core-java-modules/core-java-lang-oop-modifiers/src/main/java/com/baeldung/staticmodifier/StaticBlock.java
+++ b/core-java-modules/core-java-lang-oop-modifiers/src/main/java/com/baeldung/staticmodifier/StaticBlockDemo.java
@@ -3,7 +3,7 @@ package com.baeldung.staticmodifier;
 import java.util.LinkedList;
 import java.util.List;
 
-public class StaticBlock {
+public class StaticBlockDemo {
     private static List<String> ranks = new LinkedList<>();
 
     static {
@@ -23,6 +23,6 @@ public class StaticBlock {
     }
 
     public static void setRanks(List<String> ranks) {
-        StaticBlock.ranks = ranks;
+        StaticBlockDemo.ranks = ranks;
     }
 }
diff --git a/core-java-modules/core-java-lang-oop-modifiers/src/test/java/com/baeldung/staticmodifier/StaticBlockUnitTest.java b/core-java-modules/core-java-lang-oop-modifiers/src/test/java/com/baeldung/staticmodifier/StaticBlockDemoUnitTest.java
similarity index 80%
rename from core-java-modules/core-java-lang-oop-modifiers/src/test/java/com/baeldung/staticmodifier/StaticBlockUnitTest.java
rename to core-java-modules/core-java-lang-oop-modifiers/src/test/java/com/baeldung/staticmodifier/StaticBlockDemoUnitTest.java
index 03f3e0440c..f31a8e8895 100644
--- a/core-java-modules/core-java-lang-oop-modifiers/src/test/java/com/baeldung/staticmodifier/StaticBlockUnitTest.java
+++ b/core-java-modules/core-java-lang-oop-modifiers/src/test/java/com/baeldung/staticmodifier/StaticBlockDemoUnitTest.java
@@ -7,11 +7,11 @@ import java.util.List;
 
 import org.junit.Test;
 
-public class StaticBlockUnitTest {
+public class StaticBlockDemoUnitTest {
 
     @Test
     public void whenAddedListElementsThroughStaticBlock_thenEnsureCorrectOrder() {
-        List<String> actualList = StaticBlock.getRanks();
+        List<String> actualList = StaticBlockDemo.getRanks();
         assertThat(actualList, contains("Lieutenant", "Captain", "Major", "Colonel", "General"));
     }
 }
diff --git a/core-java-modules/core-java-lang-oop-patterns/src/main/java/com/baeldung/inheritancecomposition/model/ComputerBuilder.java b/core-java-modules/core-java-lang-oop-patterns/src/main/java/com/baeldung/inheritancecomposition/model/ComputerBuilder.java
new file mode 100644
index 0000000000..4d8574e93f
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-patterns/src/main/java/com/baeldung/inheritancecomposition/model/ComputerBuilder.java
@@ -0,0 +1,13 @@
+package com.baeldung.inheritancecomposition.model;
+
+public abstract class ComputerBuilder {
+
+    public final void buildComputer() {
+        addProcessor();
+        addMemory();
+    }
+
+    public abstract void addProcessor();
+
+    public abstract void addMemory();
+}
diff --git a/core-java-modules/core-java-lang-oop-patterns/src/main/java/com/baeldung/inheritancecomposition/model/StandardComputerBuilder.java b/core-java-modules/core-java-lang-oop-patterns/src/main/java/com/baeldung/inheritancecomposition/model/StandardComputerBuilder.java
new file mode 100644
index 0000000000..76c4732ace
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-patterns/src/main/java/com/baeldung/inheritancecomposition/model/StandardComputerBuilder.java
@@ -0,0 +1,13 @@
+package com.baeldung.inheritancecomposition.model;
+
+public class StandardComputerBuilder extends ComputerBuilder {
+    @Override
+    public void addProcessor() {
+        // method implementation
+    }
+
+    @Override
+    public void addMemory() {
+        // method implementation
+    }
+}
diff --git a/core-java-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/AnonymousInner.java b/core-java-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/AnonymousInnerTest.java
similarity index 92%
rename from core-java-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/AnonymousInner.java
rename to core-java-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/AnonymousInnerTest.java
index 9fa8ee9cd5..4e49bb5b41 100644
--- a/core-java-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/AnonymousInner.java
+++ b/core-java-modules/core-java-lang-oop-types/src/test/java/com/baeldung/nestedclass/AnonymousInnerTest.java
@@ -6,7 +6,7 @@ abstract class SimpleAbstractClass {
     abstract void run();
 }
 
-public class AnonymousInner {
+public class AnonymousInnerTest {
 
     @Test
     public void run() {