Java Input and Output - Scanner, print, println and printf

⏱️ 9 min read • Beginner Level • Lesson 19

In Java, input is commonly taken using the Scanner class, and output is displayed using methods like print(), println(), and printf().

Before learning input and output, you should understand Java variables, Java data types, and Java literals.

Scanner Class in Java

The Scanner class in Java is used to read input from different sources, such as keyboard input, files, and strings. For beginner programs, it is commonly used to take input from the keyboard using System.in.

Real World Uses of Input and Output

Common Methods of Scanner

Steps to Use Scanner in Java

Example: Taking Input Using Scanner

The following program reads a name, ID, and salary from the user using the Scanner class.

import java.util.Scanner;

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

        System.out.print("Enter Name: ");
        String name = sc.next();

        System.out.print("Enter ID: ");
        int id = sc.nextInt();

        System.out.print("Enter Salary: ");
        double salary = sc.nextDouble();

        System.out.println("----------");
        System.out.println("ID: " + id);
        System.out.println("Name: " + name);
        System.out.println("Salary: " + salary);

        sc.close();
    }
}

Sample Input:

Ayan
123
20000

Output:

Enter Name: Enter ID: Enter Salary: ----------
ID: 123
Name: Ayan
Salary: 20000.0

The nextLine() Pitfall After Numeric Input

A common beginner mistake happens when nextLine() is used after methods like nextInt(), nextDouble(), or nextFloat(). These numeric methods leave the newline character in the input buffer, and the next nextLine() reads that leftover newline.

Problem Example

import java.util.Scanner;

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

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

        System.out.print("Enter full name: ");
        String fullName = sc.nextLine(); // reads leftover newline

        System.out.println("Age: " + age);
        System.out.println("Name: " + fullName);

        sc.close();
    }
}

Output:

Enter age: 25
Enter full name:
Age: 25
Name:

Fixed Example

To fix this, call an extra nextLine() after numeric input to consume the leftover newline.

import java.util.Scanner;

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

        System.out.print("Enter age: ");
        int age = sc.nextInt();
        sc.nextLine(); // consume leftover newline

        System.out.print("Enter full name: ");
        String fullName = sc.nextLine();

        System.out.println("Age: " + age);
        System.out.println("Name: " + fullName);

        sc.close();
    }
}

Output:

Enter age: 25
Enter full name: Alice Johnson
Age: 25
Name: Alice Johnson

next() vs nextLine()

Output Methods in Java

Java provides different methods to display output on the console. The most common output methods are print(), println(), and printf().

Difference Between print() and println()

print() does not move the cursor to a new line after printing, while println() moves the cursor to the next line.

public class PrintVsPrintln {
    public static void main(String[] args) {
        System.out.print("Hello, ");
        System.out.println("world!");
        System.out.println("Bye");
    }
}

Output:

Hello, world!
Bye

printf() Method in Java

The printf() method is used for formatted printing. It works similarly to C language printf and supports format specifiers like %d, %f, %s, and %n.

System.out.printf(String format, Object... args);

Common printf Format Specifiers

public class PrintfExample {
    public static void main(String[] args) {
        int id = 42;
        double price = 123.456;
        String name = "Alice";

        System.out.printf("ID: %05d%n", id);
        System.out.printf("Price: %.2f%n", price);
        System.out.printf("Name: %-10s End%n", name);
    }
}

Output:

ID: 00042
Price: 123.46
Name: Alice      End

Common Mistakes

Interview Questions ⭐

🧠 Test your understanding with a quick quiz

Scanner sc = new Scanner(System.in);

java.util.Date now = new java.util.Date();
System.out.printf("ISO date: %___%n", now);

int x = 5;
System.out.____("Value: %d%n", x);

int age = sc.nextInt();
// fix here
String name = sc.nextLine();

Scanner sc = new Scanner(System.in);
String line = sc._____();

🎉 Great job! Continue learning Java step by step.