Scanner (User Input)

Syntax

Scanner scanner = new Scanner(System.in);

Examples

import java.util.Scanner;

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

        System.out.print("Enter your name: ");
        String name = scanner.nextLine();

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

        System.out.println("Hello " + name + ", you are " + age + " years old");
        scanner.close();
    }
}

import java.util.Scanner;

Scanner scanner = new Scanner(System.in);

System.out.print("Enter a price: ");
double price = scanner.nextDouble();

System.out.print("Are you a member? (true/false): ");
boolean isMember = scanner.nextBoolean();

double finalPrice = isMember ? price * 0.9 : price;
System.out.println("Final price: " + finalPrice);

import java.util.Scanner;

Scanner scanner = new Scanner(System.in);
int number = 0;
boolean valid = false;

while (!valid) {
    System.out.print("Enter a whole number: ");
    if (scanner.hasNextInt()) {
        number = scanner.nextInt();
        valid = true;
    } else {
        System.out.println("That's not a valid number, try again");
        scanner.next();  // discard the invalid token
    }
}

System.out.println("You entered: " + number);

Best practices

• Always close the Scanner when done (scanner.close()) to release the underlying resource, especially in larger applications
• Be careful mixing nextInt()/nextDouble() with nextLine() - the numeric methods don't consume the trailing newline, which can cause an empty read on the next nextLine() call
• Use hasNextInt(), hasNextDouble(), etc. to validate input before attempting to read it, avoiding an InputMismatchException
• Create one Scanner instance for System.in per program rather than opening multiple - reusing the same instance avoids resource conflicts

At a glance

Purpose

General-purpose application development

File extension

.java

Runs in

Java Virtual Machine

Usually used with

JDK and Java libraries

Specifications & further reading

• Java Language Specification

Related Java documentation