charAt(index)：获取字符串索引为index的字符
substring(index1, index2)：从索引index1(包含)到索引index2(不包含)截取字符串indexOf(s)：获取字符s的索引

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contains(s)：字符串是否包含字符s
split(char)：按字符char对字符串进行切分

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trim()：去除字符串两端的空白字符
Arrays.toString(sz)：将字符数组sz转成字符串