diff --git a/18_OOPS/Access_Modifier.java b/18_OOPS/Access_Modifier.java
new file mode 100644
index 0000000..173b292
--- /dev/null
+++ b/18_OOPS/Access_Modifier.java
@@ -0,0 +1,23 @@
+/**
+ * Lecture 2
+ * Access Modifier lecture
+ * Bank is a class
+ */
+public class Access_Modifier {
+    public static void main(String[] args) {
+        // creating object of BankAccount
+        BankAccount myAcc = new BankAccount();
+        myAcc.username = "Saksham";
+        myAcc.setPassword("abcd");
+    }
+}
+
+class BankAccount {
+    public String username;
+    private String password;
+
+    // setter function to set password
+    public void setPassword(String pwd) {
+        password = pwd;
+    }
+}
\ No newline at end of file
diff --git a/18_OOPS/Constructor.java b/18_OOPS/Constructor.java
new file mode 100644
index 0000000..8d2f0bd
--- /dev/null
+++ b/18_OOPS/Constructor.java
@@ -0,0 +1,25 @@
+/**
+ * Lecture 5
+ * Constructor in Java
+ * Java has its own default constructor
+ * It invokes automatically
+ */
+
+public class Constructor {
+    public static void main(String[] args) {
+        Student s1 = new Student("Shradha");
+        System.out.println(s1.name);
+    }
+
+}
+
+class Student {
+    String name;
+    int rollNo;
+
+    Student(String name) {
+        name = this.name;
+        System.out.println("Constructor is called...");
+    }
+
+}
\ No newline at end of file
diff --git a/18_OOPS/CopyConstructor.java b/18_OOPS/CopyConstructor.java
new file mode 100644
index 0000000..6f69f7e
--- /dev/null
+++ b/18_OOPS/CopyConstructor.java
@@ -0,0 +1,61 @@
+/**
+ * Lecture 8
+ * Copy Constrcutors
+ */
+public class CopyConstructor {
+    public static void main(String[] args) {
+        Student s1 = new Student();
+        s1.name = "shradha";
+        s1.rollNo = 456;
+        s1.pswd = "abcd";
+
+        s1.marks[0] = 100;
+        s1.marks[1] = 90;
+        s1.marks[2] = 80;
+
+        Student s2 = new Student(s1); // copy
+        s1.pswd = "xyz";
+        s1.marks[2] = 100;
+        for (int i = 0; i < 3; i++) {
+            System.out.println(s2.marks[i]);
+        }
+
+    }
+}
+
+class Student {
+    String name;
+    int rollNo;
+    String pswd;
+    int marks[];
+
+    class Address {
+        String city;
+    }
+
+    Student(Student s1) {
+        marks = new int[3];
+        this.name = s1.name;
+        this.rollNo = s1.rollNo;
+        this.marks = s1.marks;
+    }
+
+    // Non-Parameterised Constructors
+    Student() {
+        marks = new int[3];
+        System.out.println("Constructor is called...");
+    }
+
+    // Parametrised Constructor
+    Student(String name) {
+        marks = new int[3];
+        name = this.name;
+    }
+
+    // Parametrised Constructor
+    Student(int rollNo) {
+        marks = new int[3];
+        rollNo = this.rollNo;
+    }
+
+}
\ No newline at end of file
diff --git a/18_OOPS/Destructors.java b/18_OOPS/Destructors.java
new file mode 100644
index 0000000..21ae5ec
--- /dev/null
+++ b/18_OOPS/Destructors.java
@@ -0,0 +1,8 @@
+// lecture 9
+// Destructor
+
+public class Destructors {
+    public static void main(String[] args) {
+        // No Code Only theory
+    }
+}
diff --git a/18_OOPS/Encapsulation.java b/18_OOPS/Encapsulation.java
new file mode 100644
index 0000000..a4b1a38
--- /dev/null
+++ b/18_OOPS/Encapsulation.java
@@ -0,0 +1,12 @@
+/**
+ * Lecture 4
+ * Encapsulation
+ * One of the pillars of OOPS
+ */
+
+public class Encapsulation {
+    public static void main(String[] args) {
+        // Only theory lecture
+    }
+
+}
diff --git a/18_OOPS/Getters_Setters.java b/18_OOPS/Getters_Setters.java
new file mode 100644
index 0000000..418c984
--- /dev/null
+++ b/18_OOPS/Getters_Setters.java
@@ -0,0 +1,37 @@
+/**
+ * Leccture 3
+ * Getters and setters
+ * this - refrence to same object
+ */
+public class Getters_Setters {
+    public static void main(String[] args) {
+        // creating object of Pen
+        Pen p1 = new Pen(); // created a pen called p1 as an object
+        p1.setColor("Blue");
+        System.out.println(p1.getColor());
+        p1.setTip(5);
+        System.out.println(p1.getTip());
+        p1.setColor("yellow");
+    }
+}
+
+class Pen {
+    private String color;
+    private int tip;
+
+    String getColor() {
+        return this.color;
+    }
+
+    int getTip() {
+        return this.tip;
+    }
+
+    void setColor(String newColor) {
+        color = newColor;
+    }
+
+    void setTip(int Tip) {
+        tip = this.tip;
+    }
+}
\ No newline at end of file
diff --git a/18_OOPS/Hierarchial.java b/18_OOPS/Hierarchial.java
new file mode 100644
index 0000000..f312648
--- /dev/null
+++ b/18_OOPS/Hierarchial.java
@@ -0,0 +1,51 @@
+/**
+ * Lecture 13
+ * Hierarchial inheritance
+ */
+public class Hierarchial {
+    public static void main(String[] args) {
+        Mammal m1 = new Mammal();
+        Fish f1 = new Fish();
+        Bird b1 = new Bird();
+        m1.breathe();
+        f1.breathe();
+        b1.breathe();
+    }
+}
+
+// Base Class
+class Animal {
+    String color;
+
+    void eat() {
+        System.out.println("eating");
+    }
+
+    void breathe() {
+        System.out.println("breathing");
+    }
+}
+
+class Mammal extends Animal {
+    int legs;
+
+    void walks() {
+        System.out.println("walks");
+    }
+}
+
+class Fish extends Animal {
+    void swim() {
+        System.out.println("swimming");
+    }
+}
+
+class Bird extends Animal {
+    void fly() {
+        System.out.println("flying");
+    }
+}
+
+class Dog extends Mammal {
+    String breed;
+}
\ No newline at end of file
diff --git a/18_OOPS/Inhertitance.java b/18_OOPS/Inhertitance.java
new file mode 100644
index 0000000..af62f5e
--- /dev/null
+++ b/18_OOPS/Inhertitance.java
@@ -0,0 +1,36 @@
+/**
+ * Lecture 10
+ * Inheritance
+ * One of the pillars of OOPS
+ * 
+ */
+public class Inhertitance {
+    public static void main(String[] args) {
+        Fish shark = new Fish();
+        shark.eat();
+        shark.breathe();
+        shark.swims();
+    }
+}
+
+// Base Class
+class Animal {
+    String color;
+
+    void eat() {
+        System.out.println("eating");
+    }
+
+    void breathe() {
+        System.out.println("breathing");
+    }
+}
+
+// Derived Class
+class Fish extends Animal {
+    int fins;
+
+    void swims() {
+        System.out.println("swimming");
+    }
+}
\ No newline at end of file
diff --git a/18_OOPS/MultiLevel.java b/18_OOPS/MultiLevel.java
new file mode 100644
index 0000000..d8a73f2
--- /dev/null
+++ b/18_OOPS/MultiLevel.java
@@ -0,0 +1,35 @@
+import javax.annotation.processing.SupportedOptions;
+
+/**
+ * Lecture 12
+ * MultiLevel Inheritance
+ */
+public class MultiLevel {
+    public static void main(String[] args) {
+        Dog dobby = new Dog();
+        dobby.eat();
+        dobby.legs = 4;
+        System.out.println(dobby.legs);
+    }
+}
+
+// Base Class
+class Animal {
+    String color;
+
+    void eat() {
+        System.out.println("eating");
+    }
+
+    void breathe() {
+        System.out.println("breathing");
+    }
+}
+
+class Mammal extends Animal {
+    int legs;
+}
+
+class Dog extends Mammal {
+    String breed;
+}
diff --git a/18_OOPS/Oops.java b/18_OOPS/Oops.java
new file mode 100644
index 0000000..b7e3dd7
--- /dev/null
+++ b/18_OOPS/Oops.java
@@ -0,0 +1,41 @@
+/**
+ * Leacture 1 - Classes and Objects
+ * Classes name starts with Capital letters as a conventions
+ * new keyword - allocates memory in heap
+ * public- its a access modifier
+ */
+public class Oops {
+    public static void main(String[] args) {
+        // creating objects
+        Pen p1 = new Pen(); // created a pen called p1 as an object
+        p1.setColor("Blue");
+        System.out.println(p1.color);
+        p1.setTip(5);
+        System.out.println(p1.tip);
+        p1.color = "yellow";
+    }
+}
+
+// only one class can be puclic and it should be on top of all
+class Pen {
+    String color;
+    int tip;
+
+    void setColor(String newColor) {
+        color = newColor;
+    }
+
+    void setTip(int newTip) {
+        tip = newTip;
+    }
+}
+
+class Student {
+    String name;
+    int age;
+    float percentage; // cgpa
+
+    void calcPercentage(int phy, int chem, int mth) {
+        percentage = (phy + chem + mth) / 3;
+    }
+}
\ No newline at end of file
diff --git a/18_OOPS/TypeOfConstructor.java b/18_OOPS/TypeOfConstructor.java
new file mode 100644
index 0000000..5941937
--- /dev/null
+++ b/18_OOPS/TypeOfConstructor.java
@@ -0,0 +1,35 @@
+/**
+ * Lecture 6
+ * Types of Constructor
+ * 
+ */
+
+public class TypeOfConstructor {
+    public static void main(String[] args) {
+        Student s1 = new Student();
+        Student s2 = new Student("Shradha");
+        Student s3 = new Student(35);
+        // Student s3 = new Student("aman",35); wrong
+    }
+}
+
+class Student {
+    String name;
+    int rollNo;
+
+    // Non-Parameterised Constructors
+    Student() {
+        System.out.println("Constructor is called...");
+    }
+
+    // Parametrised Constructor
+    Student(String name) {
+        name = this.name;
+    }
+
+    // Parametrised Constructor
+    Student(int rollNo) {
+        rollNo = this.rollNo;
+    }
+
+}
\ No newline at end of file
diff --git a/18_OOPS/TypesOfInheritance.java b/18_OOPS/TypesOfInheritance.java
new file mode 100644
index 0000000..27e01c6
--- /dev/null
+++ b/18_OOPS/TypesOfInheritance.java
@@ -0,0 +1,11 @@
+/**
+ * lecture 11
+ * Types of Inheritance
+ * 
+ * 
+ */
+public class TypesOfInheritance {
+    public static void main(String[] args) {
+        // No code lecture
+    }
+}