public static boolean isAllLowerCase(CharSequence cs) {
        if (cs == null || isEmpty(cs)) {
            return false;
        }
        int sz = cs.length();
        for (int i = 0; i < sz; i++) {
            if (Character.isLowerCase(cs.charAt(i)) == false) {
                return false;
            }
        }
        return true;
    }
<p>Checks if the CharSequence contains only lowercase characters.</p>

<p>{@code null} will return {@code false}.
An empty CharSequence (length()=0) will return {@code false}.</p>

<pre>
StringUtils.isAllLowerCase(null)   = false
StringUtils.isAllLowerCase("")     = false
StringUtils.isAllLowerCase("  ")   = false
StringUtils.isAllLowerCase("abc")  = true
StringUtils.isAllLowerCase("abC") = false
</pre>

@param cs  the CharSequence to check, may be null
@return {@code true} if only contains lowercase characters, and is non-null
@since 2.5
@since 3.0 Changed signature from isAllLowerCase(String) to isAllLowerCase(CharSequence)
android/android_framework/base/src/main/java/lang3/StringUtils.java