检查字符串是否仅由具有匹配项的字母和/或连字符组成？

Question

Good evening from Cologne.

In a programming task I have to check if the given string consists only of letters and / or hyphens . Now I have an approach with matches . In the test of the word: "test-test-test" my code gives me false. It should be true. Do you know where the problem lies with me? Did I misunderstand at matches? I thank you in advance. Beautiful evening!

    public class Zeichenketten {


    public static boolean istName(String a) {

        if (a.matches("[a-zA-Z]+") || a.matches("[-]+")) {
            return true;
        }

            else {
            return false;
            } 
        }
}

Answer 1

Currently you're checking whether it's all letters, or all hyphens. You just need to check whether it matches letters or hyphens :

public static boolean istName(String a) {
    return a.matches("[a-zA-Z-]+");
}

The - at the end means "a hyphen" rather than "part of a range".

Note the simplification away from if/else - any time you write if (condition) return true; else return false; if (condition) return true; else return false; you should just write return condition; for simplicity.

Answer 2

Your code doesn't match your test string because String.matches() method returns true only when whole string matches by regex pattern. In first case: [a-zA-Z]+ you don't match because you have - symbol in the string, in second where pattern is [-]+ you don't match because you have letters in string.

Answer 3

You use wrong condition. You must create one regular expression and create good patern.

I recomended this page: https://regex101.com/ for test online regular expression.

Try this for you example:

   public static boolean istName(String a) {

        if (a.matches("[a-zA-Z-]+")) {
            return true;
        } else {
            return false;
        }
    }

Answer 4

the hyphen has the ASCII value of 45, and you know that a string is an array of characters. So you have a loop to check each character of the given string, if it finds one with the ASCI 45, return true, else return false.