Using the Scanner Class

Diapositiva 1

• To make Java programs interactive, you will want to ask and receive input from the user. Java has a class that accepts user input called Scanner.
• Before you can use the Scanner class in a program, you must import it. To do that, you code an import statement at the beginning of the program, before the class declaration:
• import java.util.Scanner;
• Note that java and util aren’t capitalized, but Scanner is.

Diapositiva 2

• Before you can use the Scanner class to read input from the console, you must declare a Scanner variable and create an instance of the Scanner class. You might want to create the Scanner variable as a class variable and create the Scanner object in the class variable initializer:
• Scanner scan = new Scanner(System.in);
• To read an input value from the user, you can use one of the methods of the Scanner class.

Scanner Class Methods

• Scanner Class Methods That Get Input Values
• Method Explanation
• boolean nextBoolean() Reads a boolean value from the user.
• double nextDouble() Reads a double value from the user.
• int nextInt() Reads an int value from the user.
• String nextLine() Reads a String value from the user.
• char nextChar() Reads a char value from the user.

Diapositiva 4

• Notice in the first column of the table that each method listing begins with the type of the value that’s returned by the method.
• The nextInt method, for example, returns an int value. Also, notice that each of the methods ends with an empty set of parentheses.
• That means that these methods don’t require parameters. If a method does require parameters, the parameters are listed within these parentheses.

Diapositiva 5

• Because these methods read a value from the user and return the value, you most often use them in statements that assign the value to a variable.
• To store the input from the user, you would use a System.out.print to prompt the user. For example:
• System.out.print(“How old are you?);
• Then you would capture the input into a variable:
• int age = scan.nextInt();
• Note the age variable could have been declared separately at the top of the program, or in combination with the initialization as shown in this example.