String.contains(CharSequence s)

最新推荐文章于 2022-02-07 11:44:05 发布

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最新推荐文章于 2022-02-07 11:44:05 发布

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分类专栏： JAVA基础

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本文详细解读了JDK中String.contains(CharSequences)方法的实现细节，包括源码解析、参数说明及具体搜索过程，帮助开发者深入了解字符串搜索机制。

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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;
    }
}