Java User Input with Scanner

The Scanner class reads input from the keyboard (or from a file or a text). You import it from java.util and give it System.in.

Read text and numbers

In the examples below we send the input from the program side, so you can see the real output. When you run it, you type the input in the terminal.

import java.util.Scanner;

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

        System.out.print("Name: ");
        String name = sc.nextLine();
        System.out.print("Age: ");
        int age = sc.nextInt();
        System.out.print("Marks: ");
        double marks = sc.nextDouble();

        System.out.println();
        System.out.println(name + ", " + age + ", " + marks);
        sc.close();
    }
}

In the output the three questions are on one line, because here the input is sent by the program and not typed by a person. In a real terminal, every answer you type comes on its own line.

Scanner methods

Method	Reads
nextLine()	A full line of text
next()	One word (until a space)
nextInt()	An int
nextDouble()	A double
nextBoolean()	true or false
nextLong()	A long
hasNextInt(), hasNextLine()	Check if there is more input of that type

The newline problem

nextInt() reads the number but leaves the Enter key (the new line) in the input. A nextLine() after it then reads an empty text. The fix: call nextLine() once to clear the line.

import java.util.Scanner;

public class Problem {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int age = sc.nextInt();
        String name = sc.nextLine();          // reads the rest of the first line: empty
        System.out.println("[" + name + "]");
    }
}

import java.util.Scanner;

public class Fixed {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int age = sc.nextInt();
        sc.nextLine();                         // clear the new line
        String name = sc.nextLine();
        System.out.println(age + " " + name);
    }
}

Check the input before reading

import java.util.Scanner;

public class Check {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        if (sc.hasNextInt()) {
            System.out.println("Number: " + sc.nextInt());
        } else {
            System.out.println("That is not a number: " + sc.next());
        }
    }
}

Read until the end

import java.util.Scanner;

public class Sum {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int total = 0;
        while (sc.hasNextInt()) {
            total += sc.nextInt();
        }
        System.out.println("Total: " + total);
    }
}

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