DEV Community: VIDHYA VARSHINI

Day 6 of Python (Dictionary, Set and Hashing)

VIDHYA VARSHINI — Sun, 15 Feb 2026 14:40:19 +0000

What is dictionary: It is a collection used to store data in key:value pairs and it is a built-in data type, mutable and ordered.

Ex:

id = { name = "Vidya",
       age : 21
       location : "Chennai"
       gender : "Female"
     }
print(id)

Output:

{'name': 'Vidya', 'age': 21, 'location': 'Chennai', 'gender': 'Female'}

Set: It is a collection of items which is unordered, does not allow duplicate values and mutable.

Ex:

num = [1,1,2,2,2,3,3,5,5,5]
freq = {}

for i in num:
    if i in freq:
        freq[i] = freq[i] + 1
    else:
            freq[i] = 1
            print(freq)

Output:

{1: 2, 2: 3, 3: 2, 5: 1}

Hashing: It is a technique that takes a key and converts it into a fixed integer value (hash value). This hash value is used to decide where to store and quickly retrieve data in memory.
Ex:

print(hash("Vidya"))

Output:

45823984723984

Hash collision: Sometimes two different keys produce same hash, which causes collision, open addressing and probing.

Day 5 of Python(Tuple, Deep copy and Shallow copy)

VIDHYA VARSHINI — Fri, 13 Feb 2026 02:32:15 +0000

What is tuple: It is a collection of items which is ordered, immutable and allows duplicates. This can also store different data types. A tuple can be identified when it is separated by a comma and no need of bracket.

Ex:

 num = 1,2,3,4,5,6
 print(num[2:5])
 print(num[3])

Output:

(3, 4, 5)
4

Single tuple: A tuple with only one item is called a single tuple.
Ex:

num = (1,)
print(type(num))

Output:

<class 'tuple'>

Deep copy: This creates a completely new copy of an object including all nested objects inside it.

Ex:

import copy
a = [[1, 2], [89, 4]]   
b = copy.deepcopy(a)       
b[1][0] = 98


print( a)
print(b)

Output:

[[1, 2], [89, 4]]
[[1, 2], [98, 4]]

Shallow copy: This creates a new outer object, but does not copy nested objects. Instead, it copies reference to them.

Ex:

import copy
a = [[1, 2], [89, 4]]   
b = copy.copy(a)       
b[1][0] = 98


print( a)
print(b)

Output:

[[1, 2], [98, 4]]
[[1, 2], [98, 4]]

Day 4 of Python(for loop and string methods)

VIDHYA VARSHINI — Fri, 13 Feb 2026 01:50:23 +0000

for loop: A for loop is used to repeat a block of code for each item in a sequence like list, tuple,string.

Syntax:

for var in range:

Ex: Print numbers from 1 to 10

for i in range(1,11):
   print(i)

Output:

Reverse a string:
To reverse a name,

name = "Vidya"
rev = name[::-1]
print(rev)

Output:

aydiV

To reverse a number,

num = 2356
rev = 0

while num > 0:
    rev = num % 10 + rev * 10
    num = num // 10

print(rev)

Output:

What is list: A list is a collection of items used to store items in single variable. This can store numbers, string. It is a built in data type. It is mutable and classified as ordered and unordered.
Ex:

list = ["apple", "orange","banana","papaya"]
list[0] = "mango"
list[1] = "strawberry"
print(list)

Output:

['mango', 'strawberry', 'banana', 'papaya']

String methods:

append - add one element at the end.
extend - add multiple elements.
insert - insert element at specific index position.
remove - removes the first occurence.
pop - removes and return element.
clear - removes all the elements.
index - returns the index value.
count - count the number of occurence.
sort - sort list in place.
reverse - reverse in place.

Day 3 of Python(while loop)

VIDHYA VARSHINI — Thu, 12 Feb 2026 07:36:58 +0000

Ternary operator: It is a one line way to write the if-else condition.

Syntax: True value if (condition) else False value
Ex: To find a given number is odd or even

if num%2 ==0:
    print("given number is even")
else:
    print("given number is odd")

Now, it can be written as

var = "num is even" if(num%2 ==0) else "num is odd"
print (var)

while loop: A while loop is used when you want to repeat the code until it satisfies the condition as true.

Ex: Print a number from 1 to 10

num = 1
while num<=10:
   print(num)
   num = num+1

Output:

Ex: To print a table with given variable

num = int(input("enter a number "))
var = 1
while var<=5:
   print(num*var)
   var = var+1

Output:

enter a number 3
3
6
9
12
15

Day 2 of Python (Operators and Conditional Statements)

VIDHYA VARSHINI — Thu, 05 Feb 2026 07:21:03 +0000

What is operators: Operators in general are used to perform operations on values and variables.

Types of operators:

Arithmetic operators: It is used to perform basic mathematical operations like addition, subtraction, multiplication etc.
Comparison operators: It is used to compare values and it will return either true or false according to the given condition.
Logical operators: It is used to perform Logical AND, Logical OR and Logical NOT operations. This is used to combine conditional statements. 4.** Assignment operators:** It is used to assign values to the variables. This is used to assign the value of right side of the expression to the left side operand.

Formatted string(f): It is used to insert variables or values directly inside a string.

name = input("What is your name ")
print("Your name is ",name)
age =int( input("What is your age "))
print("Your age is ",age)
gender = input("What is your gender ")
print("Your gender is ",gender)
print(f"Your name is {name} age {age} gender {gender}")

Output:

What is your name Vidya
Your name is  Vidya
What is your age 20
Your age is  20
What is your gender Female
Your gender is  Female
Your name is Vidya age 20 gender Female

By default, input from the user will be stored as string.

Typecasting: It means converting from one data type to another. There are two types of typecasting are there :

Implicit typecasting : It automatically converts from one data type to another without writing any extra code.
Explicit typecasting : It is manually converting from one data type to another type by the programmer.

String: It is a sequence of characters used to represent data. This can be given inside single quote(' '), double quote(" ") and triple quote(""" """) for multiple strings.

Indexing: This means accessing the individual elements using their position number index position.
Negative indexing: This means accessing elements from the end of a sequence using negative numbers.
Slicing: This means extracting a part from a sequence like a string,list.

Conditional Statements: This is used to make decisions in a program. They help the program choose what to do based on the given condition.
Types of conditional statements:

if statement - This is used to execute code only if the condition is true.
if-else statement - This is used when there are two choices.
elif statement - This is used when there are multiple conditions.

Getting started with Python

VIDHYA VARSHINI — Wed, 04 Feb 2026 06:51:55 +0000

Introduction:
What is programming: It is a way of communicating with the machine using binary code.
What is interpreter: An interpreter translates and executes code step-by-step instead of converting the whole program into machine code at once.
What is compiler: It is a program that translates high level source code into machine code (binary).

How python files run at backend: After entering as python3 filename, it will first convert into byte code.
python.py → bytecode (.pyc) → executed by PVM
This will run on every server.
Python is both compiler and interpreted language.

nano linux commands:

pwd - print working directory (to check where the file is located).
mkdir - make directory
ls - list
cd - change directory
rmdir - remove directory

import this - displays the Zen of Python
quit() - to get exit from the program.

Indentation - It is the spaces (or tabs) given at the beginning of the line of code.

Swapping of two variables:

a = 17
b = 5
a = a+b
b = a-b
a = a-b
print(a,b)

Output:

5 17

This can also be done using tuple method.

a = 10
b = 5
a,b = b,a
print(a,b)

Output:

5 10

Exception Handling in Java

VIDHYA VARSHINI — Tue, 20 Jan 2026 17:03:24 +0000

What is exception handling: The term "exception" is simply known as "exceptional event", which means it occurs during the execution of a program, that disrupts the normal flow of the program's instructions.

When an error occurs within a method, the method creates an object and hands it off to the runtime system.
The object, called an exception object, contains information about the error, including its type and the state of the program when the error occurred.
Creating an exception object and handing it to the runtime system is called throwing an exception.
After a method throws an exception, the runtime system attempts to find something to handle it.
The set of possible "somethings" to handle the exception is the ordered list of methods that had been called to get to the method where the the error occurred. The list of methods is known as the "call stack".

package exceptionhandling;

public class Arithmeticexception {

    public static void add(int a, int b) {
        System.out.println(a+b);
    }

    public static void sub(int a, int b) {
        System.out.println(a-b);
    }

    public static void divide(int a, int b) {
        System.out.println(a/b);
    }



    public static void main(String[] args) {
     int a = 10;
     int b = 5;
     add(a,b);
     sub( a, b);
     divide( a, b);

Output:

15
5
2

Abstraction in Java

VIDHYA VARSHINI — Thu, 18 Dec 2025 17:03:32 +0000

What is abstraction: It is the process of showing only necessary details and hiding internal implementation details. If one method is declared as abstract in a class, then whole class is defined as abstract class. Abstraction hides the complex details and shows only essential features.

The abstract keyword is a non-access modifier, used for classes and methods.
Abstract class: It is a restricted class where objects cannot be created. If it needs to be accessed, it must be inherited from another class.

Abstract method : This can be used only in abstract class and it does not have a body. The body is provided by the subclass.

We cannot create an object for an abstract class because it may contain abstract methods without implementation, which makes the class incomplete.

Rules for abstraction:

Abstract - if a method doesn't have body, the method is abstract method.
If atleast one method is abstract, then the entire class is abstract class.
Abstract method don't have body and should not be given body.

Method overriding in Java

VIDHYA VARSHINI — Mon, 15 Dec 2025 11:43:48 +0000

What is method overriding: When a subclass provides a specific implementation for a method that is already defined in its parent class, it is called method overriding. The overridden method in the subclass must have the same name, parameters, and return type as the method in the parent class.

Rules for method overriding:
a) Name, parameters and return type must be of same type as parent.
b) Static methods cannot be overridden.
c) At runtime, Java selects the method based on the real object in memory rather than the reference type.
d) Method overriding requires inheritance.

Static methods cannot be overridden, defining a static method in a subclass with same signature as in the super-class hides the super-class method.
Instance methods can be overridden, but a subclass cannot override a super-class static method.
A static method in a subclass with the same signature as a super-class static method hides the original method.
Private methods cannot be overridden because they are not visible to sub-classes.
A subclass method with the same name is treated as a new, independent method, unrelated to the parent class.

Access Modifier in Java

VIDHYA VARSHINI — Mon, 15 Dec 2025 11:17:18 +0000

What is access modifier: It is a keyword in Java that controls who can access a class, variable, method, or constructor. There are 4 types of access modifiers in Java. They are:
a) public
b) protected
c) default
d) private

1. public: This can be accessed from anywhere(same class, same package, different package). It is used when a class or member should be visible to all.

2. private: Accessible only within the same class. Used for data hiding and security.

3. default: Accessible only within the same package. Used when access should be restricted to the package.

4. protected: Accessible within the same package and in sub-classes of other packages. Mainly used to support inheritance.

Package in Java

VIDHYA VARSHINI — Mon, 15 Dec 2025 10:37:15 +0000

What is package: A package is used to group related classes. It is like a folder in a file directory. These are used to avoid name conflicts and to write a better maintainable code. It is divided into two categories :
a) Built-in package
b) User-defined package

Built-in package: The Java API is a library of pre-written classes, that are free to use, included in the Java Development Environment.
Some of the commonly used built-in packages are:
a) java.lang
b) java.io
c) java.util

User-defined package: These are the packages which are defined by the user. It helps us organize our own classes properly. We need to use user-defined packages because
a) To organize large projects
b) To avoid class name conflicts
c) To improve code readability
d) To control access using access modifiers

History of Java

VIDHYA VARSHINI — Mon, 15 Dec 2025 09:51:22 +0000

Java was started in 1991 by James Gosling as part of a research initiative called the Green Project. The main objective of this project was to create a programming language that could run on electronic devices such as televisions and set-top boxes. The team aimed to develop a language that was simple, reliable, secure, and independent of hardware platforms.

During this early phase, the language was named Oak, inspired by an oak tree located outside James Gosling’s office. Oak emphasized portability and safety, two core principles that later became the foundation of Java.

In 1995, Oak was renamed Java due to trademark issues and was officially released to the public. This release marked a major milestone because Java introduced the groundbreaking concept of platform independence through the Java Virtual Machine (JVM). Instead of compiling programs into machine-specific code, Java source code was compiled into bytecode, which could run on any system equipped with a JVM.

This “write once, run anywhere” feature made Java especially attractive during the rapid expansion of the internet. As a result, Java applets became widely used for adding interactive and dynamic content to web pages.