Java：验证字符串是否仅由另一个字符串的字母组成

Question

I want to make a function who have String a and String b. I want to verify if String a is formed only by characters/letters from String b.

Ex:

String a="abz";
    String b="abecxe";

The result is false, because String b is not contain 'z' from String a.

Thank you!

Answer 1

Assuming you can write code to protect against null/invalid input:

return b.replaceAll("["+a+"]", "").length() == 0;

As pointed out this will fail for arbitrary Strings.

for (int i = 0; i < b.length(); i++) {
    if (!a.contains(b.substring(i, i + 1)) {
        return false;
    }
}
return true;

Again, you write the validation.

Answer 2

One very straightforward way to do this is to write a method that converts a String into a set of characters, then take advantage of the removeAll method of the Set interface. You might need the Apache ArrayUtils class to convert the char[] from your String into a Character[] .

It could look like this.

public static boolean containsOnlyCharactersFrom(String first, String second) {
    return charactersIn(first).removeAll(charactersIn(second)).isEmpty();
}

private static Set<Character> charactersIn(String argument) {
    Character[] characterArray = ArrayUtils.toObject(argument.toCharArray());
    return new HashSet<Character>(Arrays.asList(characterArray));
}

Answer 3

Thanks to all!

i solve the problem with String matching(i tried this method in the past but i was wrong):

if ( a.matches("[" + b + "]+")) {
                      label1.setText("The String a contains only letters from String b!");
                  } else {
                      label2.setText("The String a contains more letters than String b!");
                  }