Capstone: stdin, FizzBuzz, and beyond

Reading input

Everything so far hardcoded its data. Real judged problems — on this platform, in interviews, in competitive programming — hand your program its data through standard input (stdin), the text stream a program can read at runtime, and grade whatever you print to standard output. Master this handshake and every DSA problem becomes: read, solve, print. Java's tool is Scanner:

import java.util.Scanner;

Scanner in = new Scanner(System.in);
int a = in.nextInt();       // next whole number
double d = in.nextDouble(); // next decimal
String w = in.next();       // next single word
String line = in.nextLine(); // rest of the line

nextInt skips spaces and line breaks on its own, so "3 4" and "3\n4" both work. One classic trap: after nextInt(), a following nextLine() first consumes the leftover end-of-line, often returning "". Call in.nextLine() once to flush before reading a real line.

You now hold the whole toolkit

Look back at what each unit handed you:

• syntax, types, and the compiler (units 1-2)
• branching and loops (unit 3), methods (unit 4)
• classes, encapsulation, inheritance, interfaces (units 5-6)
• ArrayList, HashMap, HashSet (unit 7), generics and exceptions (unit 8)
• lambdas and streams (unit 9), big-O, StringBuilder, and the two core interview patterns (unit 10)

That is enough Java to work through the DSA platform's problem sets, where every solution is a class reading stdin and writing stdout, exactly like this lesson. Finish with the rite of passage below.