Reading from Keyboard in Java

JAVA language provides a Class called Scanner that is used for reading data from different sources.

Here KEYBOARD is a source.

So, How to read data from the keyboard?

We have a Scanner class that is present in the UTIL package of Java.

Now, We have some methods that are necessary to read the Scanner and there are different methods as following:

nextInt( ) nextFloat( ) nextDouble( ) next( ) nextLine( ) nextByte( ) nextShort( ) nextLong( ) nextBoolean( ) hasNextInt( ) hasNextFloat( )

The selection of the method depends on the type of information or data you required from a user.

For example:

1. If you are requesting the age of a person, then you require a number from the user. The number is an Integer type and hence, you will call the method nextInt( ) to read the numbers from the keyboard.
2. If you request a single word from the user, then use next( ).
3. If you request a collection of words or lines, then use nextLine( ).

Let's see How to use the Scanner class with a example:

Step 1: Create Object

Scanner sc = new Scanner(System.in);

Here, Scanner(left) is a class name. Sc is a reference. new Scanner is a constructor. System. in is an object associated with the Keyboard.

Example: Add any two numbers.

Step 2: Declare variables.

int a,b,c;

Step 3: Give the message to the system that you want to take some number from the keyboard.

System.out.println("Enter two numbers");

Step 4: For reading a number, we need to call out a method and store a value in a variable.

a = s.nextInt( );

b = s.nextInt( );

c= a+b;

Since the type of data is an Integer, we use the method nextInt( );

Once we call this [nextInt( );] method, It will read integer numbers from the keyboard.

Basically, s.nextInt( ); will get Integer from the keyboard and store in variable a and b.

Step 5: Print the result

System.out.println("Sum is " + c);

Example 2: Take the name of a person as input and give the Welcome message as Output.

Important: What is a use of hasNextInt( ) and hasNextFloat?

Answer: This method is use to check if the data is an integer/float type or not before reading.

Reminder: System.out.println("Hello" + c); prints "HelloMahadev" and hence it is WRONG. System.out.println("Hello " + c); prints "Hello Mahadev" and hence it is RIGHT.