How to tell if a random string is an email address or something else

- Try the below code, this may be helpful to you.

public class EmailCheck {

    public static void main(String[] args){


        String email = "[email protected]";
        Pattern pattern = Pattern.compile("[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}");
        Matcher mat = pattern.matcher(email);

        if(mat.matches()){

            System.out.println("Valid email address");
        }else{

            System.out.println("Not a valid email address");
        }
    }

}

- Also take a look at this site, which shows another deeper validation using regular expression. Deeper validation using regular expression

You can use following for verifying an email;

String email ="[email protected]"
Pattern p = Pattern.compile(".+@.+\\.[a-z]+");
Matcher m = p.matcher(email);
boolean matchFound = m.matches();
if (matchFound) {
    //your work here
}

Thanks to @Dukeling

private static toLowerCaseIfEmail(String string) {
    try {
        new InternetAddress(string, true);
    } catch (AddressException e) {
        return string;
    }
    if (string.trim().endsWith("]")) {
        return string;
    }
    int lastAt = string.lastIndexOf('@');
    if (lastAt == -1) {
        return string;
    }
    return string.substring(0,lastAt)+string.substring(lastAt).toLowerCase();
}

should, from what I can tell, do the required thing.

Update

Since the previous one ignored the possibility of (comment) syntax after the last @... which lets face it, if we see them should just bail out fast and return the string unmodified

private static toLowerCaseIfEmail(String string) {
    try {
        new InternetAddress(string, true);
    } catch (AddressException e) {
        return string;
    }
    int lastAt = string.lastIndexOf('@');
    if (lastAt == -1 
        || string.lastIndexOf(']') > lastAt
        || string.lastIndexOf(')' > lastAt) {
        return string;
    }
    return string.substring(0,lastAt)+string.substring(lastAt).toLowerCase();
}