scanner.rst

Scanner

Receiving user data is an important part of coding to interact with the user. To receive input from the user, the Scanner class is used. This is found under the java.util package.

Hence we will need to import the library first,

import java.util.Scanner;

Note

This is the most important step and also the easiest to forget. If the Scanner class is not implemented, all its function and instances cannot be used.

Now we can use the Scanner class by creating an object of the class.

Scanner input = new Scanner(System.in);

The line above creates a Scanner instance input that will read the user input depending on the methods called. The following are the eight most common methods to retrieve user input depending on the data type.

Methods	Return Type
nextByte()	Byte
nextShort()	Short
nextInt()	Int
nextLong()	Long
nextFloat()	Float
nextDouble()	Double
nextLine()	String
nextBoolean	Boolean

Important

It is important that the input type matches the method's data type, or else you will get an exception/error message.

Setting up with Scanner class

import java.util.Scanner; // Import Scanner library

class TestClass 
{
   public static void main(String[] args)
   {
      // Create an instance of the Scanner class
      Scanner input = new Scanner(System.in);

      // Source code as follows
   }
}

Byte

System.out.println("Enter a byte integer:");

// Reading the input as byte data type
byte aByte = input.nextByte(); 
System.out.println("aByte = " + aByte);

Output

Enter a byte integer:
5
aByte = 5

Short

System.out.println("Enter a short integer:");

// Reading the input as short data type
short aShort = input.nextShort();
System.out.println("aShort = " + aShort);

Output

Enter a short integer:
50
aShort = 50

Int

System.out.println("Enter a integer:");

// Reading the input as a int data type
int aInt = input.nextInt();
System.out.println("aInt = " + aInt);

Output

Enter a integer:
100
aInt = 100

Long

System.out.println("Enter a long integer:");

// Reading the input as a long data type
long aLong = input.nextLong();
System.out.println("aLong = " + aLong);

Output

Enter a long integer:
12345
aLong = 12345

Float

System.out.println("Enter a float:");

// Reading the input as a float data type
float aFloat = input.nextFloat();
System.out.println("aFloat = " + aFloat);

Output

Enter a float:
95.43
aFloat = 95.43

Double

System.out.println("Enter a double:");

// Reading the input as a double data type
double aDouble = input.nextDouble();
System.out.println("aDouble = " + aDouble);

Output

Enter a double:
97584.45
aDouble = 97584.45

String

System.out.println("Enter a string:");

// Reading the input as a string data type
String aString = input.nextLine();
System.out.println("aString = " + aString);

Output

Enter a string:
Hello World
aString = Hello World

Boolean

System.out.println("Enter a boolean:");

// Reading the input as a boolean variable
boolean aBoolean = input.nextBoolean();
System.out.println("aBoolean = " + aBoolean);

Output

Enter a boolean:
true
aBoolean = true

Example

The following block of code shows an example of using the Scanner library.

import java.util.Scanner; // Import Scanner library

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

     System.out.print("Please enter your name: ");
     String name = input.nextLine();

     System.out.println("Hi " + name + ", what is your favourite number?");
     int num = input.nextInt();

     System.out.println("Your favourite number is " + num + ".");
   }
}

Output

Please enter your name: Jack
Hi Jack, what is your favourite number?
7
Your favourite number is 7.