How to check if a string contains uppercase java

With streams, you can to the following.

key.chars().anyMatch(Character::isUpperCase)

This is much lighter than regexes in terms of resources.

Just use the proper regex with matcher.find()

Pattern.compile("[A-Z]").matcher(key).find()

Or you can do it as described by sopheamak here: How do I check if a Java String contains at least one capital letter, lowercase letter, and number?

In your example that would be:

else if (!key.equals(key.toLowerCase())

If one of the letters in key is uppercase it will not match the result of key.toLowerCase() and thus return true because of !.

You can use Apache Commons Lang (https://commons.apache.org/proper/commons-lang/). Is has a method for this:

else if (StringUtils.containsAny(key, "QWERTYUIOPASDFGHJKLZXCVBNM")){
    UI.println("Invalid, key contains a space, illegal character");
}

You can do it as follows:

public class Main {
    public static void main(String args[]) {
        String[] keys = { "HELLO", "Hello", "hello", "hello world", "Hello World" };
        for (String key : keys) {
            if (key.matches(".*[A-Z].*")) {
                System.out.println("'" + key + "' contains invalid, key contains a space, illegal character");
            } else {
                System.out.println("'" + key + "' passed the check");
            }
        }
    }
}

Output:

'HELLO' contains invalid, key contains a space, illegal character
'Hello' contains invalid, key contains a space, illegal character
'hello' passed the check
'hello world' passed the check
'Hello World' contains invalid, key contains a space, illegal character

If you use Guava, you can get it using the powerful CharMatcher:

First compile the matcher as a static member of the class so that it's done once and you don't need to recompute it at every call.

private static final CharMatcher UPPERCASE_LETTER = CharMatcher.inRange('A', 'Z');

Change it to whatever letters you actually want. For instance if you want some accentuated characters, you can extend the following:

private static final CharMatcher UPPERCASE_LETTER = CharMatcher.inRange('A', 'Z')
                                                               .or(CharMatcher.anyOf("ÁÀÄÂÉÈËÊÍÌÏÎÓÒÖÔÚÙÜÛ"));

If you're lazy and just want to delegate to Character::isUpperCase, that's also possible:

private static final CharMatcher UPPERCASE_LETTER = CharMatcher.forPredicate(Character::isUpperCase)

Then in your code, write the following:

if (UPPERCASE_LETTER.matchesAnyOf(key)) {
  // Do what you want
}

If you took the streams solution of @OlivierGrégoire and want limit it to the Capitals [A-Z] you can get it by also testing the UnicodeBlock as BASIC_LATIN. Where BASIC_LATIN is the ASCII Block of Unicode(see BASIC_LATIN )

        key.chars().anyMatch(this::isBasicLatinCapital)
        ...
        private boolean isBasicLatinCapital( int c) {
        return
            Character.UnicodeBlock.BASIC_LATIN == Character.UnicodeBlock.of(c) && Character.isUpperCase(c) ;
        }