Remove all characters from the string except letters and numbers in Java

@Luchnik, you were not on the right track.

public class HelloWorld {
    public static void main (String... av) {

        String s = "  --abc  678 .. Z";

        System.out.println("End "+delNoDigOrLet(s));
    }

    private static String delNoDigOrLet (String s) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < s.length(); i++) {
            if (Character .isLetterOrDigit(s.charAt(i)))
                sb.append(s.charAt(i));
        }
        return sb.toString();
    }
}

Here's how you can try

String s = "буквы,символы,цифры и тд и тп";
s = s.replaceAll("[^A-Za-zА-Яа-я0-9]", ""); // удалится все кроме букв и цифр

Sit down and read about the lines, instead of writing garbage

String resultString = str.replaceAll("some char", "some other char");

UPD1

What's wrong with my option? what prevents you from putting signs instead of letters/numbers as the first parameter?

The code may not work =)

public class HelloWorld {
    public static void main (String... av) {

        String s = "  --abc  678 .. Z";

        System.out.println("End "+delNoDigOrLet(s));
    }

    private static String delNoDigOrLet (String s) {
        for (int i = 0; i < s.length(); i++) {
            if (!Character.isLetterOrDigit(s.charAt(i)))
              String str = s.replaceAll(str.charAt(i), "");

        }
        return str;
    }
}

Well, or it is better to store the "forbidden" characters in some array-dictionary and replace them in the string with the same search.

Hi, I myself faced the problem of how to remove all the letters from the string and leave only the numbers. It was this topic that prompted the answer :) My modification at the request of the author:

import java.util.Scanner;
public class test {

    public static void main(String[] args) {
        int n = 0;
        String textDigits = "";
        Scanner sc = new Scanner(System.in);
        System.out.print("Введите свой текст: ");
        String self = sc.nextLine();

        for (char ch : self.toCharArray()) {
            if ( Character.isLetterOrDigit(ch) ) {
                textDigits = textDigits + ch;
            }else{
                n++;
            }
        }
        System.out.println("Количество других символов: " + n);
        System.out.println( textDigits );
    }
}

You can do this : It also removes spaces.

String resultString = str.replaceAll("[^A-Za-zА-Яа-я0-9 ]", "");

I'm for the functionalka:

private static String delNoDigOrLet(String str) {
    return str.chars()
            .filter(i -> Character.isLetterOrDigit(i))
            .mapToObj(i -> String.valueOf((char) i))
            .collect(Collectors.joining());
}

If you solve the problem using a regular expression, you can use

String result = self.replaceAll("[^\\p{L}\\p{N}]+", "");

If you need to leave whitespace characters:

String result = self.replaceAll("(?U)[^\\p{L}\\p{N}\\s]+", "");

See example of how a regular expression works.

Details

• (?U) - modifier Pattern.UNICODE_CHARACTER_CLASS (not used in Android!), which in this expression allows \s to find all Unicode whitespace characters, not just ASCII
• [^ - the beginning of an exclusive (negating) character of the class, it finds any character other than those specified in the class:
  • \p{L} - any Unicode letter
  • \p{N} - any Unicode digit
  • \s - thanks to (?U) finds any Unicode whitespace character
• ]+ - end of character class, 1 or more repeats (for faster deletion).

See example of how Java code works:

System.out.println("Я – робот123!N".replaceAll("[^\\p{L}\\p{N}]+", ""));
// => Яробот123N