Why Even Experienced Java Developers Misunderstand isEmpty vs. isBlank

A new colleague with three years of Java experience still confuses the behavior of isEmpty and isBlank, prompting a detailed walkthrough of the org.apache.commons.lang3.StringUtils utility class.

isEmpty series

StringUtils.isEmpty()

Checks whether a CharSequence is null or has a length of zero. A single space character is **not** considered empty, so isEmpty(" ") returns false.

StringUtils.isEmpty(null) = true
StringUtils.isEmpty("") = true
StringUtils.isEmpty(" ") = false
StringUtils.isEmpty("bob") = false
StringUtils.isEmpty(" bob ") = false
/* NOTE: This method changed in Lang version 2.0.
   It no longer trims the CharSequence. That functionality is now available in isBlank(). */
public static boolean isEmpty(final CharSequence cs) {
    return cs == null || cs.length() == 0;
}

StringUtils.isNotEmpty()

Simply the negation of isEmpty().

public static boolean isNotEmpty(final CharSequence cs) {
    return !isEmpty(cs);
}

StringUtils.isAnyEmpty()

Returns true if **any** of the supplied CharSequence arguments is null or empty.

StringUtils.isAnyEmpty(null) = true
StringUtils.isAnyEmpty(null, "foo") = true
StringUtils.isAnyEmpty("", "bar") = true
StringUtils.isAnyEmpty("bob", "") = true
StringUtils.isAnyEmpty(" bob ", null) = true
StringUtils.isAnyEmpty(" ", "bar") = false
StringUtils.isAnyEmpty("foo", "bar") = false
public static boolean isAnyEmpty(final CharSequence... css) {
    if (ArrayUtils.isEmpty(css)) {
        return true;
    }
    for (final CharSequence cs : css) {
        if (isEmpty(cs)) {
            return true;
        }
    }
    return false;
}

StringUtils.isNoneEmpty()

Equivalent to !isAnyEmpty(css); returns true only when **all** arguments are non‑null and non‑empty.

StringUtils.isNoneEmpty(null) = false
StringUtils.isNoneEmpty(null, "foo") = false
StringUtils.isNoneEmpty("", "bar") = false
StringUtils.isNoneEmpty("bob", "") = false
StringUtils.isNoneEmpty("  bob  ", null) = false
StringUtils.isNoneEmpty(" ", "bar") = true
StringUtils.isNoneEmpty("foo", "bar") = true
public static boolean isNoneEmpty(final CharSequence... css) {
    return !isAnyEmpty(css);
}

isBlank series

StringUtils.isBlank()

Considers null, the empty string, and strings consisting solely of whitespace as "blank".

StringUtils.isBlank(null) = true
StringUtils.isBlank("") = true
StringUtils.isBlank(" ") = true
StringUtils.isBlank("bob") = false
StringUtils.isBlank(" bob ") = false
public static boolean isBlank(final CharSequence cs) {
    int strLen;
    if (cs == null || (strLen = cs.length()) == 0) {
        return true;
    }
    for (int i = 0; i < strLen; i++) {
        if (!Character.isWhitespace(cs.charAt(i))) {
            return false;
        }
    }
    return true;
}

StringUtils.isNotBlank()

Negates isBlank().

public static boolean isNotBlank(final CharSequence cs) {
    return !isBlank(cs);
}

StringUtils.isAnyBlank()

Returns true if **any** of the supplied arguments is blank (null, empty, or whitespace only).

StringUtils.isAnyBlank(null) = true
StringUtils.isAnyBlank(null, "foo") = true
StringUtils.isAnyBlank(null, null) = true
StringUtils.isAnyBlank("", "bar") = true
StringUtils.isAnyBlank("bob", "") = true
StringUtils.isAnyBlank(" bob ", null) = true
StringUtils.isAnyBlank(" ", "bar") = true
StringUtils.isAnyBlank("foo", "bar") = false
public static boolean isAnyBlank(final CharSequence... css) {
    if (ArrayUtils.isEmpty(css)) {
        return true;
    }
    for (final CharSequence cs : css) {
        if (isBlank(cs)) {
            return true;
        }
    }
    return false;
}

StringUtils.isNoneBlank()

Returns true only when **none** of the arguments are blank.

StringUtils.isNoneBlank(null) = false
StringUtils.isNoneBlank(null, "foo") = false
StringUtils.isNoneBlank(null, null) = false
StringUtils.isNoneBlank("", "bar") = false
StringUtils.isNoneBlank("bob", "") = false
StringUtils.isNoneBlank("  bob  ", null) = false
StringUtils.isNoneBlank(" ", "bar") = false
StringUtils.isNoneBlank("foo", "bar") = true
public static boolean isNoneBlank(final CharSequence... css) {
    return !isAnyBlank(css);
}

Other StringUtils methods

For a complete list of useful utilities, refer to the official Apache Commons Lang documentation.