This document discusses using a Scanner object in Java to read input from the user. It explains that System.in represents standard input and can be passed to a new Scanner object. Various Scanner methods like nextInt(), nextDouble(), and nextLine() allow retrieving input as different data types. The document provides examples of creating a Scanner, importing it, and using methods like nextInt() and nextLine() to read integer and string user input. It emphasizes the importance of prompts to indicate what type of data the user should enter.

1. Java Input
Prepared by:
Jean Michael Castor

2. Introduction
• For some unfathomable reason, Java has
never made it very easy to read data typed in
by the user of a program.

3. Introduction
• You've already seen that output can be
displayed to the user using the subroutine
System.out.print. This subroutine is part of a
pre-defined object called System.out. The
purpose of this object is precisely to display
output to the user.

4. • There is also a corresponding object called
System.in that exists to read data input by the
user, but it provides only very primitive input
facilities, and it requires some advanced Java
programming skills to use it effectively.
• To use System.in, a Java Scanner is used that
will get the inputs.

5. Scanner Creation/Declaration
Scanner keyboard = new Scanner(System.in);
• Scanner is a class which must be instantiated before it
can be used. In other words, you must make a new
Scanner if you want to use Scanner. A reference
must be used to store the location in memory of the
Scanner object created.
• System.in is the parameter passed to the Scanner
constructor so that Java will know to connect the new
Scanner to the keyboard. keyboard is a reference that
will store the location of newly created Scanner object.
Reference variable Object Instantiation

6. Scanner Imports
• In order to use Scanner, you must import
java.util.Scanner.
import java.util.Scanner;

7. Scanner Methods
NAME USE
nextInt(); Returns the next integer value
nextDouble(); Returns the next double value
nextFloat(); Returns the next float value
nextLong(); Returns the next long value
nextShort(); Returns the next short value
next(); Returns the next one word String value
nextLine(); Returns the next multiple word String value

8. Reading in Integers
Scanner keyboard = new Scanner(System.in);
System.out.print(“ Enter Value”);
int num = keyboard.nextInt();
• The nextInt() method is used to tell a Scanner object to
retrieve the next integer value entered.
• In the example, the next integer typed in on the keyboard
would be read in and placed in the integer variable num.
• nextInt() will read up to the first whitespace value
entered.

9. Integers
int num = keyboard.nextInt();
• The nextInt() method will read in the next
integer. If a non-integer value is encountered such as
a decimal value, the result will be run-time
exception.
• keyboard is a reference that refers to a Scanner
object.
method callreference variabledata type
identifier

10. Strings
String word= keyboard.nextLine();
• The nextLine() method will read in the next text
value entered. A numeric or non-numeric text value will
be accepted.
• In the example, the next text entered on the keyboard
would be read in and placed in variable word.
• The nextLine() method would read up to the first
whitespace encountered. Whitespace would be any
space, any tab, or any enter key.
method callreference variabledata type
identifier

11. Prompts
System.out.print(“Enter an integer: ”);
• When performing input operations, it is a
must to use prompts. A prompt is a way of
indicating to a user what type of data to enter.
• The prompt above indicates that an integer
value is expected.