Question

import java.util.Scanner;

public class MatchesMethodTest {

    public static void main(String[] args) {    
        String s;

        Scanner input = new Scanner(System.in);
        System.out.print("Input one real number to one decimal place and one natural number(ex. 1.4 5): ");
        s = input.next();

        if (s.matches("\\f{1} \\d{1}$"))
            System.out.print("You input correctly.");
        else
            System.out.print("You input incorrectly.");
    }
}

The user should input one real number to one decimal place and one natural number. The program prints whether user inputs correctly or not. So when I input 1.4 and 5, I want the program to print “You input correctly”, but it outputs “You input incorrectly” instead. How can I fix this problem?

Answer 1

In a regular expression, \f doesn’t match a floating point number, as you seem to want it to do – it matches a special kind of character called the “form-feed character.”

Try changing your regular expression match to:

s.matches("\\d{1}\\.\\d{1} \\d{1}$")

This checks for a single digit, a period, a digit, a space, and a final digit. (Note that your “natural number” is limited to one digit by the {1} term.)

Edit: You may also need to change input.next() to input.nextLine(), since the .next() method may only grab the first integer. Untested.