public static boolean contains(CharSequence seq, int searchChar) {
        if (isEmpty(seq)) {
            return false;
        }
        return CharSequenceUtils.indexOf(seq, searchChar, 0) >= 0;
    }
<p>Checks if CharSequence contains a search character, handling {@code null}.
This method uses {@link String#indexOf(int)} if possible.</p>

<p>A {@code null} or empty ("") CharSequence will return {@code false}.</p>

<pre>
StringUtils.contains(null, *)    = false
StringUtils.contains("", *)      = false
StringUtils.contains("abc", 'a') = true
StringUtils.contains("abc", 'z') = false
</pre>

@param seq  the CharSequence to check, may be null
@param searchChar  the character to find
@return true if the CharSequence contains the search character,
 false if not or {@code null} string input
@since 2.0
@since 3.0 Changed signature from contains(String, int) to contains(CharSequence, int)
android/android_framework/base/src/main/java/lang3/StringUtils.java