java中的正则表达式及其与indexOf相比的性能 [英] Regex in java and its performance compared to indexOf

问题描述

请有人告诉我如何匹配_"和句号."使用正则表达式在字符串中仅一次，使用 indexOf() 而不是正则表达式更有效.

Please can someone tell me how to match "_" and a period "." excatly one time in a string using regex, Also is it more efficient using indexOf() instead of regex expression.

String s= "Hello_Wor.ld"  or 
s="12323_!£££$.asdfasd"

基本上任何字符都可以在_和之前和之后出现.唯一的要求是整个字符串应该只包含一次_和<代码>.

bascially any no of characters can come before and after _ and . the only requirement is that the entire string should only contain one occurance of _ and .

推荐答案

indexOf 将比正则表达式快得多，也可能更容易理解.

indexOf will be much quicker than a regex, and will probably also be easier to understand.

只测试是否 indexOf('_') >= 0，然后如果 indexOf('_', indexOfFirstUnderScore) <0.对这段时间做同样的事情.

Just test if indexOf('_') >= 0, and then if indexOf('_', indexOfFirstUnderScore) < 0. Do the same for the period.

private boolean containsOneAndOnlyOne(String s, char c) {
    int firstIndex = s.indexOf(c);
    if (firstIndex < 0) {
        return false;
    }
    int secondIndex = s.indexOf(c, firstIndex + 1);
    return secondIndex < 0;
}

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