String.contains(CharSequence s)

jdk中对String.contains(CharSequence s) 方法的实现：

    /**     * Code shared by String and StringBuffer to do searches. The     * source is the character array being searched, and the target     * is the string being searched for.     *     * @param   source       the characters being searched.     * @param   sourceOffset offset of the source string.     * @param   sourceCount  count of the source string.     * @param   target       the characters being searched for.     * @param   targetOffset offset of the target string.     * @param   targetCount  count of the target string.     * @param   fromIndex    the index to begin searching from.     */    //如果返回值大于-1即表示原字符串中包含目标字符串    static int indexOf(char[] source, int sourceOffset, int sourceCount,                       char[] target, int targetOffset, int targetCount,                       int fromIndex) {        if (fromIndex >= sourceCount) {            return (targetCount == 0 ? sourceCount : -1);        }        if (fromIndex < 0) {            fromIndex = 0;        }        if (targetCount == 0) {            return fromIndex;        }        char first = target[targetOffset];//目标字符串的首位字符        int max = sourceOffset + (sourceCount - targetCount);//max表示在匹配过程中，原字符向后移动时的范围限制        for (int i = sourceOffset + fromIndex; i <= max; i++) {            /* Look for first character. */            if (source[i] != first) {                while (++i <= max && source[i] != first);            }            /* Found first character, now look at the rest of v2 */            if (i <= max) {                int j = i + 1;                int end = j + targetCount - 1;                for (int k = targetOffset + 1; j < end && source[j]                        == target[k]; j++, k++);                if (j == end) {                    /* Found whole string. */                    return i - sourceOffset;                }            }        }        return -1;    }}