RKTechGame | Scanner & PrintWriter (Deep Explained)

Scanner Class – User/Input Read karne ke Pro Tips!

Scanner class (java.util package) ka use ham mostly user se console input lene, ya file se data padhne ke liye karte hain. Ye kaafi flexible hai – alag alag data types ke liye instantly input read kar sakte ho!

Key Features

• Multiple sources se input: stdin, file, string, stream.
• Int, Float, String, Double, Boolean... har tarah ke input easily le lo!
• Whitespace delimiter se tokens extract karta hai. (next() sirf ek word, nextLine() poori line deta)
• Methods: nextInt(), nextLine(), nextDouble(), hasNext()

Common Use & Gotchas

• Console input: Scanner sc = new Scanner(System.in);
• File input: Scanner sc = new Scanner(new File("input.txt"));
• nextInt() ke baad agar nextLine() use karo toh blank line mil sakti hai (kyunki newline consume nahi hota).
• Kabhi bhi ek program mein ek hi Scanner object use karo, warna exceptions aa sakte hain.

Example 1: Console se input

import java.util.Scanner;
public class ScannerDemo {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.print("Naam batao: ");
    String name = sc.nextLine();

    System.out.print("Umra batao: ");
    int age = sc.nextInt();

    System.out.println("Hello " + name + ", Age: " + age);
    sc.close();
  }
}

Example 2: File se input

Scanner sc = new Scanner(new File("data.txt"));
while(sc.hasNextLine()) {
  String line = sc.nextLine();
  System.out.println(line);
}
sc.close();

Advanced Tip

• Scanner se CSV ya structured data line by line read kar sakte ho. split() ka use karo for more control.

PrintWriter Class – Powerful Writing/Output!

PrintWriter class (java.io package) ka use text files, console ya network streams mein formatted data likhne ke liye hota hai. Ye FileWriter ya OutputStream se zyada flexible hai.

Key Features

• Text data, numbers, objects – sab likho print(), println(), printf() se
• Auto flush ka option hai: stream automatically flush ho jata hai after println() or printf()
• Exceptions suppress kar leta hai, checkError() se pata chalta hai koi problem hui ya nahi
• Formatting C/C++ jaise: printf("%s %d", name, age)
• FileWriter, OutputStream, StringWriter sab wrap kar sakte ho

Example 1: File Me Text Write Karna

import java.io.*;
public class PrintWriterDemo {
  public static void main(String[] args) {
    try {
      PrintWriter pw = new PrintWriter(new FileWriter("output.txt"));
      pw.println("Hello World!");
      pw.printf("Name: %s Age: %d", "Amit", 22);
      pw.close();
      System.out.println("File written!");
    } catch(Exception e) {
      e.printStackTrace();
    }
  }
}

Example 2: Direct Console Output

PrintWriter pw = new PrintWriter(System.out, true); // autoFlush on
pw.println("Yeh console par print hoga!");
pw.close();

Pro Tips & Limitations

• BufferedWriter ka internal buffer milta hai – performance best rahti hai!
• Always close() karo, nahi toh data file mein na jaye.
• PrintWriter exceptions throw nahi karta – debugging me dikkat ho sakti hai, checkError() ka use karo.

Real-world Example: Scanner + PrintWriter Combo

Competitive programming ya exams mein aksar user input le ke file me likhna padta hai. Scanner se input lo, PrintWriter se save karo, super easy:

Scanner sc = new Scanner(System.in);
PrintWriter pw = new PrintWriter(new FileWriter("log.txt"));
while(sc.hasNextLine()) {
  String line = sc.nextLine();
  pw.println(line); // File me save
}
pw.close();
sc.close();