Unit 5: Loops, Arrays & Enums

🛒 How Flipkart Shows You Millions of Products in Milliseconds

Open Flipkart and search "wireless earbuds." Within 200 milliseconds, the app returns thousands of products — sorted by relevance, price, rating, and availability. Behind the scenes, Java code iterates through arrays of millions of product objects using optimised loops. Each product's price, rating, stock count, and seller info is stored in arrays and traversed using for loops, filtered using if conditions inside while loops, and categorised using enum types (ELECTRONICS, FASHION, HOME, etc.).

At NSE India, the Nifty 50 index recalculates every second during trading hours. A stock price analyzer takes an array of 375 one-minute candle prices (6.25 hours × 60 minutes), loops through them to compute moving averages, find day-high/day-low, detect crossover patterns, and flag breakout signals. Every one of these operations is fundamentally a loop iterating over an array.

Zerodha's Kite platform processes 15 million+ orders daily. Their backend, largely written in Java and Go, uses enum types for order status (PENDING, EXECUTED, CANCELLED, REJECTED) and arrays for real-time tick data. Without loops and arrays, modern trading platforms simply cannot exist.