How to check if a String contains only ASCII?

This will return true if String only contains ASCII characters and false when it does not

Charset.forName("US-ASCII").newEncoder().canEncode(str)

If You want to remove non ASCII , here is the snippet:

if(!Charset.forName("US-ASCII").newEncoder().canEncode(str)) {
                        str = str.replaceAll("[^\\p{ASCII}]", "");
                    }

In Java 8 and above, one can use String#codePoints in conjunction with IntStream#allMatch.

boolean allASCII = str.codePoints().allMatch(c -> c < 128);

In Kotlin:

fun String.isAsciiString() : Boolean =
    this.toCharArray().none { it < ' ' || it > '~' }

private static boolean isASCII(String s) 
{
    for (int i = 0; i < s.length(); i++) 
        if (s.charAt(i) > 127) 
            return false;
    return true;
}