M3: Using Scanner to read int, double and String values

Scanner scnr;

Declare reference variable named scnr of class Scanner.

scnr = new Scanner(System.in);

Assign the reference to a new instance of Scanner to the scnr variable. Since the Scanner refers to System.in, calling methods using the reference will obtain data from the user (standard input).

scnr.nextInt()

Read the next token and return as an int value. Skip any leading whitespace and stop at whitespace following token. Will throw an InputMismatchException if the token is not an integer.

whitespace

space, tab and newline characters

scnr.next()

Read the next token (non-whitespace characters) and return the reference to a string containing those characters. Skip any leading whitespace and stop at whitespace following token.

scnr.nextDouble()

Read the next token and return as a double value. Skip any leading whitespace and stop at whitespace following token. Will throw an InputMismatchException if the token is not a floating point number.

scnr.nextLine()

Read all characters (including whitespace) up to and including the next newline (\n) character. Return a reference to a string containing all the characters except for the newline.

name = scnr.next();

A statement to read in the next token as a String and save the reference into the name variable.

token

a sequence of non-whitespace characters

InputMismatchException

In Scanner methods, if the token read doesn't match the expected data type then this exception is thrown.

NoSuchElementException

In Scanner methods, if there is not any more input then this exception is thrown.

IllegalStateException

In Scanner methods, if the scanner has already been closed then this exception is thrown.

scnr.close();

Closes the instance of the Scanner, typically called when the programmer is done reading from it.

String line = scnr.nextLine();

A statement to declare the variable line to be datatype String. The nextLine() method call returns a reference to a String that is saved in line. This string will contain all the characters up to but not including the next newline character. The newline character is read but not returned.

double price;
price = scnr.nextDouble();

Declares a variable. Reads and returns the next token as a double saving value in the variable.

char choice;
choice = scnr.next().charAt(0);

Declares a variable. Reads the next token and returns the first character of the token and saves the character in the variable.