模仿String.indexOf,判断一个字符串是否包含另一个字符串

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目录：
一.方法介绍
二.图示意
三.源代码

一.方法介绍

判断一个字符串str1是否包含另一个字符串str2：
1.取str2的第一个字符一次和str1的字符依次比较，知道找到相等的字符为止或者找完整个str1的length.
2.当找到相等的字符后，在str2长度内str2与str1依次进行比较

二.图示意



三.源代码

JDK中java.lang.String.indexOf(char[], int, int, char[], int, int, int)源码:

/**
     * 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.
     */
    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];
        int max = sourceOffset + (sourceCount - targetCount);

        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;
    }

模仿的判断一个字符串是否包含另一个字符串的源码：

public static String compareDoubleString(String source, String target) {
		// 分别获取两个字符串的长度，因为后面会用到
		int sourceLength = source.length();
		int targetLength = target.length();

		// 获取目标的第一个字符
		char firstTargetChar = target.charAt(0);

		// 最多比较的次数
		int max = sourceLength - targetLength;
		// 如果第一个不相等，那么一直找到相等的那一个或者找完都不能找到
		int sourceOffset = -1;
		while (++sourceOffset < max
				&& source.charAt(sourceOffset) != firstTargetChar) {
		}
		if (sourceOffset <= max) {
			// 设置新的源索引
			int newSourceOffset = sourceOffset + 1;
			// 剩余的比较长度，也就是在offset上增加targetLength
			int leaveLength = newSourceOffset + targetLength - 1;
			int targetOffset = 1;
			// 连续的比较，条件不符合的时候跳出
			for (; newSourceOffset < leaveLength
					&& source.charAt(newSourceOffset) == target
							.charAt(targetOffset); newSourceOffset++, targetOffset++)
				;
			if (newSourceOffset == leaveLength) {
				return "包含：source包含target字符串!";
			}
		}
		return "不包含：source不包含target字符串!";
	}

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