Java How to validate characters using a string?

Question

I am working on a java project and was wondering how I could use a string to determine whether or not the chars in an array are valid. The given string is final String ALLOWED_CHARS = "01".

Say I have 2 char arrays:

char[] valid = {0,0,1,0,0,0,1,1,0,1}
char[] invalid = {0,0,1,0,0,A,1,1,0,1}

What would be an efficient way of determining valid and invalid arrays using the ALLOWED_CHARS string? I assume I am going to need to loop through the array and somehow compare each char to the chars in ALLOWED_CHARS but I'm not sure how to go about doing it.

Answer 1

You could form strings from the input character arrays and then use String#matches along with a regex pattern.

final String ALLOWED_CHARS = "01";
String regex = "[" + ALLOWED_CHARS + "]+";

char[] valid = {'0', '0', '1', '0', '0', '0', '1', '1', '0', '1'};
char[] invalid = {'0', '0', '1', '0', '0', 'A', '1', '1', '0', '1'};
String s1 = new String(valid);
String s2 = new String(invalid);

System.out.println(s1 + " valid? " + s1.matches(regex));
System.out.println(s2 + " valid? " + s2.matches(regex));

This prints:

0010001101 valid? true
00100A1101 valid? false

Answer 2

import java.util.*;
import java.util.stream.*;

class Main {
  static final String ALLOWED_CHARS = "01";
  
  public static void main(String[] args) {
    char[] valid = {'0','0','1','0','0','0','1','1','0','1'};
    char[] invalid = {'0','0','1','0','0','A','1','1','0','1'};
    
    Set<Character> set = ALLOWED_CHARS.chars()
                                      .mapToObj(c -> (char) c)
                                      .collect(Collectors.toSet());

    isValid(set, valid);
    isValid(set, invalid);
  }

  public static void isValid(Set<Character> set, char[] array) {
    for (char c: array) {
      if (!set.contains(c)) {
        System.out.println("Invalid");
        return;
      }
    }
    System.out.println("Valid");
  }
}

Another approach (other than regex) — add the ALLOWED_CHARS to a Set and simple check if any element in the array is not present in the Set.