Java Basic Input and Output

Java Output

In Java, you can simply use System.out.println(), System.out.print(), or System.out.printf() to send output to standard output (screen).

• System is a class
• out is a public static field: it accepts output data.

1. println() vs print() vs printf()

• println(): Prints the text and moves to the next line.
• print(): Prints the text and stays on the same line.
• printf(): Prints formatted strings (like C/C++).

System.out.println("Hello");
System.out.print("World");
System.out.println("!");
// Output:
// Hello
// World!

2. Formatting with printf()

You can use format specifiers to format your output.

• %d: Integer
• %f: Float/Double
• %s: String
• %n: New Line

int age = 25;
String name = "John";
System.out.printf("My name is %s and I am %d years old.%n", name, age);

Java Input

Java provides different ways to get input from the user. The most common way is using the Scanner class.

1. Using Scanner Class

First, import the Scanner class.

import java.util.Scanner;

Then, create an object of Scanner and use its methods.

import java.util.Scanner;

class Input {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter an integer: ");
        int number = input.nextInt();
        System.out.println("You entered " + number);

        // Close the scanner
        input.close();
    }
}

Scanner Methods

2. Using BufferedReader (Fast I/O)

For competitive programming or reading large files, Scanner can be slow. BufferedReader is faster.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Enter your name: ");
        String name = reader.readLine();
        System.out.println("Hello, " + name);
    }
}

Key Takeaways

• Output: Use System.out.println() to print text and move to a new line. Use print() to stay on the same line.
• Input: Use the Scanner class to read user input.
• Import: You must import java.util.Scanner; before using it.

Common Pitfalls

[!WARNING] Closing Scanner: Always close your scanner with input.close() when you're done to prevent resource leaks.

[!WARNING] NextLine Issue: Mixing nextInt() and nextLine() can be tricky. nextInt() reads the number but leaves the "enter" key press in the buffer, which nextLine() might accidentally read as an empty string. Fix: Call input.nextLine() once after nextInt() to consume the leftover newline.

Challenge