Core Java and Backend Development

Topics

• What Java is, write once run anywhere, the JVM, why Java dominates enterprise hiring in India
• JDK vs JRE vs JVM, what you install and why JDK 21 is the right choice in 2026
• Installing JDK 21 and IntelliJ IDEA Community Edition, project structure, src folder, packages intro
• Your first Java class, public static void main, the entry point every interview asks about
• System.out.println, printing strings and numbers, escape sequences
• Comments, single-line and multi-line, why readable code matters in interviews
• Compiling and running, javac and java from terminal, then running from IntelliJ
• Java naming conventions, camelCase for variables and methods, PascalCase for classes
• Primitive types overview, int, double, boolean, char, and why Java is strongly typed

Hands-on

• Hello World in three forms: println, concatenation, formatted output with printf
• A program that prints your name, college, and target company (TCS, Infosys, etc.)
• A simple calculator that prints sum, difference, product, and quotient of two hardcoded numbers
• A program that prints the current date using java.time (first exposure to the standard library)

Every exercise compiles and runs on day one. You leave knowing how to create a project, write a class, and fix a compile error without panic.

Topics

• Variables and literals, declaration, assignment, final keyword intro
• Primitive types in depth, byte, short, int, long, float, double, boolean, char
• Arithmetic operators, +, -, *, /, %, operator precedence, integer division traps
• Relational and logical operators, == vs .equals preview for strings
• Increment and decrement, prefix vs postfix, common interview trick questions
• Type casting, implicit and explicit, widening vs narrowing
• Scanner class, reading integers, doubles, strings, handling newline after nextInt
• Math class, pow, sqrt, abs, min, max
• Formatted output, System.out.printf, format specifiers for integers and decimals

Hands-on

• Simple interest and compound interest calculator
• Currency notes dispenser (given amount, print note breakdown)
• Temperature converter with user input
• Employee salary calculator (basic + HRA + deductions)
• Swap two numbers without a third variable (classic interview warm-up)

Topics

Methods:

• Why methods, reusability, single responsibility, readable main method
• Method declaration, return types, void, parameters, call stack intro
• Pass by value in Java, primitives vs reference types in parameters
• Method overloading, same name different signatures
• Recursion, base case, factorial and Fibonacci, when recursion is appropriate

Arrays:

• Array declaration, creation, length property, index bounds
• Iterating arrays, for and enhanced for
• Multi-dimensional arrays, 2D arrays for tables and grids
• Common algorithms, find max/min, sum, average, linear search, bubble sort intro

Hands-on

• Method library: isPrime, isPalindrome, countDigits, reverseNumber, gcd, lcm
• Array statistics: max, min, second largest, frequency of an element
• Matrix addition and multiplication (2x2 and 3x3)
• Student marks array: average, highest, count above threshold

Topics

Strings:

• String immutability, string pool concept, why == vs .equals matters
• Common methods: length, charAt, substring, indexOf, contains, replace, split, trim
• StringBuilder and StringBuffer, when to use mutable strings
• String comparison, compareTo, equalsIgnoreCase
• Character class, isDigit, isLetter, Character.toUpperCase
• StringTokenizer intro, split with regex basics

Exception handling:

• Exception hierarchy, Throwable, Exception, RuntimeException vs checked exceptions
• try-catch, multiple catch blocks, finally block
• throw and throws, creating meaningful error messages
• Custom exceptions, when they improve readability
• Best practices, do not catch Exception blindly, fail fast with clear messages

Hands-on

• Palindrome checker (with and without StringBuilder reverse)
• Password strength validator with specific rules
• Email format validator (basic pattern check without libraries)
• Word count and character frequency in a sentence
• ATM with exception handling for insufficient balance and invalid input

Topics

• Collections hierarchy overview, Iterable, Collection, List, Set, Map
• ArrayList, add, get, remove, size, iteration, when to use ArrayList
• LinkedList, when list operations at ends matter
• HashSet, uniqueness, contains performance
• HashMap, key-value pairs, get, put, containsKey, iteration over entrySet
• Iterator and enhanced for loop with collections
• Comparable and Comparator, sorting custom objects
• Collections utility class, sort, reverse, shuffle, max, min
• Choosing the right collection, interview justification questions

Hands-on

• Student list with ArrayList (add, search, delete, sort by name)
• Word frequency counter with HashMap
• Remove duplicates from a list using HashSet
• Phone directory with HashMap (name to phone, multiple numbers)
• Top N frequent elements in an array (interview pattern)

Assessment

• Given five problem descriptions, choose List, Set, or Map, implement, and write one sentence justifying the choice

Topics

• Client-server model, HTTP methods GET POST PUT DELETE, status codes
• What is Spring Boot, convention over configuration, why companies use it
• Creating a Spring Boot project in IntelliJ, application.properties
• @RestController, @GetMapping, @PostMapping, request and response bodies
• JSON with Jackson, returning objects from endpoints
• JDBC recap, connecting MySQL to Spring Boot, simple CRUD queries
• @Autowired and service layer intro, separating controller from business logic
• Testing APIs with Postman, reading responses, common error codes

Hands-on

• Hello REST API with two GET endpoints
• Student REST API: add student, list students, get by id (in-memory then JDBC)
• Postman collection exported and saved to GitHub

You leave able to answer: "Have you worked with Spring Boot?" with a real project link, not a textbook definition.