Understanding Apache Commons Lang StringUtils: isEmpty, isBlank, and Related Methods

isEmpty Series

StringUtils.isEmpty()

Checks whether a CharSequence is null or has a length of zero. Note that a string containing only a space character is not considered empty.

StringUtils.isEmpty(null)    = true
StringUtils.isEmpty("")      = true
StringUtils.isEmpty(" ")     = false
StringUtils.isEmpty("bob")   = false
StringUtils.isEmpty(" bob ") = false

Implementation:

public static boolean isEmpty(final CharSequence cs) {
    return cs == null || cs.length() == 0;
}

StringUtils.isNotEmpty()

Returns the negation of isEmpty() .

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

StringUtils.isAnyEmpty()

Returns true if any of the supplied CharSequences 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()

Returns true only when all supplied CharSequences are non‑null and non‑empty (i.e., the negation of isAnyEmpty() ).

public static boolean isNoneEmpty(final CharSequence... css) {
    return !isAnyEmpty(css);
}

isBlank Series

StringUtils.isBlank()

Checks whether a CharSequence is null, empty, or contains only whitespace characters.

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 CharSequences is 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 supplied CharSequences are null, empty, or whitespace only (i.e., the negation of isAnyBlank() ).

public static boolean isNoneBlank(final CharSequence... css) {
    return !isAnyBlank(css);
}

For a complete reference, see the official Apache Commons Lang documentation.