Java Input and Output Basics - Advanced

Overview of Input and Output in Java

Java me Input aur Output (I/O) programming ka ek bahut important hissa hai jo user se data lene aur processed data ko display karne me madad karta hai. Java me standard streams use kiye jaate hain jo keyboard input, console output aur error output ke liye predefined hote hain.

Standard Streams

Standard Input (System.in): Keyboard se data read karta hai. Ye byte stream hai.
Standard Output (System.out): Console par normal output display karta hai.
Standard Error (System.err): Program ke errors ko display karta hai.

Example jisme teeno streams ka use dikhaya gaya hai:

import java.util.Scanner;

public class IOStreamsExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        try {
            System.out.print("Enter a number: ");
            int num = scanner.nextInt();
            System.out.println("You entered: " + num);
            System.err.println("This is an error message.");
        } catch (Exception e) {
            System.err.println("Invalid input!");
        } finally {
            scanner.close();
        }
    }
}

Scanner Class for User Input

The standard way to read user input in Java is by using the Scanner class from java.util package.

Import karne ke liye: import java.util.Scanner;
Input ke liye different methods: nextInt(), nextLine(), nextDouble(), etc.
User input ko handle karna easy aur readable hota hai.

Printing Output in Java

Output dikhane ke liye Java me teen main methods hai:

System.out.print() - Text print karta hai cursor ke next line par na jaakar.
System.out.println() - Text print karta hai aur cursor ko next line par le jata hai.
System.out.printf() - Format specified output ke liye, jaise integer, decimal formatting.

System.out.print("Hello ");
System.out.print("World!");
System.out.println(" Welcome.");
System.out.printf("Pi value: %.2f", 3.14159);

Important Notes

System.in ek byte stream hai, isliye Scanner ka use karke hi user-friendly input lena chahiye.
User se input lene ke baad input stream ko close() karna best practice hai.
nextInt() ke baad agar nextLine() use karna ho to ek extra nextLine() lagana padta hai buffer clear karne ke liye.
System.err errors ko alag dikhane ke liye use hota hai jisse debugging easy hoti hai.