How can I read input from the console using the Scanner class in Java?

Question

A simple example to illustrate how java.util.Scanner works would be reading a single integer from System.in. It's really quite simple.

Scanner sc = new Scanner(System.in);
int i = sc.nextInt();

To retrieve a username I would probably use sc.nextLine().

System.out.println("Enter your username: ");
Scanner scanner = new Scanner(System.in);
String username = scanner.nextLine();
System.out.println("Your username is " + username);

You could also use next(String pattern) if you want more control over the input, or just validate the username variable.

You'll find more information on their implementation in the API Documentation for java.util.Scanner

Scanner scan = new Scanner(System.in);
String myLine = scan.nextLine();

Reading Data From The Console

• BufferedReader is synchronized, so read operations on a BufferedReader can be safely done from multiple threads. The buffer size may be specified, or the default size(8192) may be used. The default is large enough for most purposes.

  readLine() « just reads data line by line from the stream or source. A line is considered to be terminated by any one these: \n, \r (or) \r\n

• Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace(\s) and it is recognised by Character.isWhitespace.

  « Until the user enters data, the scanning operation may block, waiting for input. « Use Scanner(BUFFER_SIZE = 1024) if you want to parse a specific type of token from a stream. « A scanner however is not thread safe. It has to be externally synchronized.

  next() « Finds and returns the next complete token from this scanner. nextInt() « Scans the next token of the input as an int.

Code

String name = null;
int number;

java.io.BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
name = in.readLine(); // If the user has not entered anything, assume the default value.
number = Integer.parseInt(in.readLine()); // It reads only String,and we need to parse it.
System.out.println("Name " + name + "\t number " + number);

java.util.Scanner sc = new Scanner(System.in).useDelimiter("\\s");
name = sc.next();  // It will not leave until the user enters data.
number = sc.nextInt(); // We can read specific data.
System.out.println("Name " + name + "\t number " + number);

// The Console class is not working in the IDE as expected.
java.io.Console cnsl = System.console();
if (cnsl != null) {
    // Read a line from the user input. The cursor blinks after the specified input.
    name = cnsl.readLine("Name: ");
    System.out.println("Name entered: " + name);
}

Inputs and outputs of Stream

Reader Input:     Output:
Yash 777          Line1 = Yash 777
     7            Line1 = 7

Scanner Input:    Output:
Yash 777          token1 = Yash
                  token2 = 777

There is problem with the input.nextInt() method - it only reads the int value.

So when reading the next line using input.nextLine() you receive "\n", i.e. the Enter key. So to skip this you have to add the input.nextLine().

Try it like that:

 System.out.print("Insert a number: ");
 int number = input.nextInt();
 input.nextLine(); // This line you have to add (it consumes the \n character)
 System.out.print("Text1: ");
 String text1 = input.nextLine();
 System.out.print("Text2: ");
 String text2 = input.nextLine();

There are several ways to get input from the user. Here in this program we will take the Scanner class to achieve the task. This Scanner class comes under java.util, hence the first line of the program is import java.util.Scanner; which allows the user to read values of various types in Java. The import statement line should have to be in the first line the java program, and we proceed further for code.

in.nextInt(); // It just reads the numbers

in.nextLine(); // It get the String which user enters

To access methods in the Scanner class create a new scanner object as "in". Now we use one of its method, that is "next". The "next" method gets the string of text that a user enters on the keyboard.

Here I'm using in.nextLine(); to get the String which the user enters.

import java.util.Scanner;

class GetInputFromUser {
    public static void main(String args[]) {
        int a;
        float b;
        String s;

        Scanner in = new Scanner(System.in);
        System.out.println("Enter a string");
        s = in.nextLine();
        System.out.println("You entered string " + s);

        System.out.println("Enter an integer");
        a = in.nextInt();
        System.out.println("You entered integer " + a);

        System.out.println("Enter a float");
        b = in.nextFloat();
        System.out.println("You entered float " + b);
    }
}

import java.util.Scanner;

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

        String username;
        double age;
        String gender;
        String marital_status;
        int telephone_number;

        // Allows a person to enter his/her name   
        Scanner one = new Scanner(System.in);
        System.out.println("Enter Name:" );  
        username = one.next();
        System.out.println("Name accepted " + username);

        // Allows a person to enter his/her age   
        Scanner two = new Scanner(System.in);
        System.out.println("Enter Age:" );  
        age = two.nextDouble();
        System.out.println("Age accepted " + age);

        // Allows a person to enter his/her gender  
        Scanner three = new Scanner(System.in);
        System.out.println("Enter Gender:" );  
        gender = three.next();
        System.out.println("Gender accepted " + gender);

        // Allows a person to enter his/her marital status
        Scanner four = new Scanner(System.in);
        System.out.println("Enter Marital status:" );  
        marital_status = four.next();
        System.out.println("Marital status accepted " + marital_status);

        // Allows a person to enter his/her telephone number
        Scanner five = new Scanner(System.in);
        System.out.println("Enter Telephone number:" );  
        telephone_number = five.nextInt();
        System.out.println("Telephone number accepted " + telephone_number);
    }
}

You can make a simple program to ask for the user's name and print whatever the reply use inputs.

Or ask the user to enter two numbers and you can add, multiply, subtract, or divide those numbers and print the answers for user inputs just like the behavior of a calculator.

So there you need the Scanner class. You have to import java.util.Scanner;, and in the code you need to use:

Scanner input = new Scanner(System.in);

input is a variable name.

Scanner input = new Scanner(System.in);

System.out.println("Please enter your name: ");
s = input.next(); // Getting a String value

System.out.println("Please enter your age: ");
i = input.nextInt(); // Getting an integer

System.out.println("Please enter your salary: ");
d = input.nextDouble(); // Getting a double

See how this differs: input.next();, i = input.nextInt();, d = input.nextDouble();

According to a String, int and a double varies the same way for the rest. Don't forget the import statement at the top of your code.