Input/Scanner

What is Scanner?

Scanner is a java util class that provides the developer the simplest way to read user input from the command line and store that input under different data types.

What is the Scanners Purpose?

Developers often need to read runtime input. This input comes in the form of text and is stored as Strings inside the program code. Java provides multiple means to read input from the user or data files, but Scanner is the simplest method.

How do you read runtime user input?

Declaration:

Scanner scanner = new Scanner(System.in);

Reading User Input:

int value = scanner.nextInt();
double value = scanner.nextDouble();

//read the next single word
String value = scanner.next();

//read the entire line
String value = scanner.nextLine();

InputMismatchException

Occurs when the wrong type of data is entered. You might expect int to be entered, but instead receive String.

How do you read Text Files?

while (scanner.hasNext()) {
    System.out.println(scanner.nextLine());
}
scanner.close();

What is File

Used to identify a file on the hard disc.

Declaration:"

File file = new File("filename");

Using with scanner:

Scanner scanner = new Scanner(file);

throws file not found exception

Good Practice to have with File

Do not use direct file name, use file.seperator to get a relative file name.

validate for file is not null and file.exists() and throw filenotfoundexception otherwise.

toString()

Displays the field values or state of object. It is an inherited and overridden method from object needing teh @Override tag

you can auto generate it, remember not to manipualte the data or format it. Just display whatever the value is and the dat.a No logic no format. For debugging.