Programming Questions

Practical, no-fluff answers to core programming concepts — plus dedicated interview-question sets for SQL, Java, Python, and JavaScript.

• What is the difference between a compiler and an interpreter?
  A compiler translates an entire program into machine code before it runs, while an interpreter translates and executes c…
• What is object-oriented programming?
  Object-oriented programming (OOP) is a programming style that organizes code around "objects" combining data and behavio…
• What is the difference between a stack and a queue?
  A stack is Last-In-First-Out (LIFO) — the last item added is the first removed — while a queue is First-In-First-Out (FI…
• What is recursion in programming?
  Recursion is when a function calls itself to solve a smaller version of the same problem, until it reaches a base case s…
• What is the difference between synchronous and asynchronous programming?
  In synchronous code, each operation waits for the previous one to finish before running; in asynchronous code, operation…
• What is the difference between SQL's WHERE and HAVING clauses?
  WHERE filters individual rows before any grouping happens, while HAVING filters groups after a GROUP BY has aggregated t…
• What is a primary key in SQL?
  A primary key is a column (or set of columns) that uniquely identifies each row in a table, and cannot contain duplicate…
• What is the difference between INNER JOIN and LEFT JOIN in SQL?
  INNER JOIN returns only rows that match in both tables, while LEFT JOIN returns all rows from the left table, with NULLs…
• What is normalization in SQL databases?
  Normalization is the process of organizing database tables to reduce data redundancy and prevent inconsistencies, by spl…
• What is the difference between DELETE and TRUNCATE in SQL?
  DELETE removes rows one at a time and can be filtered with a WHERE clause, while TRUNCATE instantly removes all rows in …
• What is the difference between JDK, JRE, and JVM?
  The JVM runs compiled Java code, the JRE bundles the JVM with core libraries needed to run programs, and the JDK adds th…
• What is the difference between an interface and an abstract class in Java?
  An interface defines a contract of methods a class must implement, with no shared implementation (traditionally), while …
• What is the difference between == and .equals() in Java?
  == compares whether two references point to the exact same object in memory, while .equals() compares whether two object…
• What is method overloading vs method overriding in Java?
  Overloading means having multiple methods with the same name but different parameters in the same class; overriding mean…
• What is the difference between ArrayList and LinkedList in Java?
  ArrayList stores elements in a resizable array, giving fast random access but slower inserts/deletes in the middle; Link…
• What is the difference between a list and a tuple in Python?
  A list is mutable — its contents can be changed after creation — while a tuple is immutable, meaning once created, its c…
• What are Python decorators?
  A decorator is a function that wraps another function to add extra behavior, without permanently modifying the original …
• What is the difference between deep copy and shallow copy in Python?
  A shallow copy creates a new object but still references the same nested objects as the original, while a deep copy recu…
• What is the Global Interpreter Lock (GIL) in Python?
  The GIL is a lock in the standard Python interpreter that allows only one thread to execute Python bytecode at a time, e…
• What is the difference between *args and **kwargs in Python?
  *args lets a function accept any number of extra positional arguments, collected into a tuple, while **kwargs collects a…
• What is the difference between var, let, and const in JavaScript?
  var is function-scoped and can be redeclared; let is block-scoped and can be reassigned but not redeclared; const is blo…
• What is a closure in JavaScript?
  A closure is a function that remembers and can access variables from the scope it was created in, even after that outer …
• What is the difference between == and === in JavaScript?
  == compares two values after converting them to the same type if needed ("loose equality"), while === compares both valu…
• What is event delegation in JavaScript?
  Event delegation is a technique where you attach a single event listener to a parent element instead of separate listene…
• What is the difference between null and undefined in JavaScript?
  undefined means a variable has been declared but not yet assigned a value, while null is an intentional value explicitly…