替换字符串中的许多字符的有效方法是什么？ [英] What is an efficient way to replace many characters in a string?

问题描述

Java中的字符串处理是我努力学习做得好的事情。目前我想接受一个字符串并替换我找到的任何字符。

String handling in Java is something I'm trying to learn to do well. Currently I want to take in a string and replace any characters I find.

这是我目前效率低下的（有点愚蠢的IMO）功能。它被写成只是工作。

Here is my current inefficient (and kinda silly IMO) function. It was written to just work.

public String convertWord(String word)
{
    return word.toLowerCase().replace('á', 'a')
                             .replace('é', 'e')
                             .replace('í', 'i')
                             .replace('ú', 'u')
                             .replace('ý', 'y')
                             .replace('ð', 'd')
                             .replace('ó', 'o')
                             .replace('ö', 'o')
                             .replaceAll("[-]", "")
                             .replaceAll("[.]", "")
                             .replaceAll("[/]", "")
                             .replaceAll("[æ]", "ae")
                             .replaceAll("[þ]", "th");
}

我跑了1.000.000次，耗时8182ms。那么我应该如何继续更改此功能以提高效率？

I ran 1.000.000 runs of it and it took 8182ms. So how should I proceed in changing this function to make it more efficient?

找到解决方案：

转换函数到这个

public String convertWord(String word)
{
    StringBuilder sb = new StringBuilder();

    char[] charArr = word.toLowerCase().toCharArray();

    for(int i = 0; i < charArr.length; i++)
    {
        // Single character case
        if(charArr[i] == 'á')
        {
            sb.append('a');
        }
        // Char to two characters
        else if(charArr[i] == 'þ')
        {
            sb.append("th");
        }
        // Remove
        else if(charArr[i] == '-')
        {
        }
        // Base case
        else
        {   
            sb.append(word.charAt(i));
        }
    }

    return sb.toString();
}

运行此功能1.000.000次需要518ms。所以我觉得这很有效率。感谢帮助人员：）

Running this function 1.000.000 times takes 518ms. So I think that is efficient enough. Thanks for the help guys :)

推荐答案

您可以创建一个String []表，其长度为Character.MAX_VALUE。 （包括映射到小写）

You could create a table of String[] which is Character.MAX_VALUE in length. (Including the mapping to lower case)

由于替换变得更复杂，执行它们的时间将保持不变。

As the replacements got more complex, the time to perform them would remain the same.

private static final String[] REPLACEMENT = new String[Character.MAX_VALUE+1];
static {
    for(int i=Character.MIN_VALUE;i<=Character.MAX_VALUE;i++)
        REPLACEMENT[i] = Character.toString(Character.toLowerCase((char) i));
    // substitute
    REPLACEMENT['á'] =  "a";
    // remove
    REPLACEMENT['-'] =  "";
    // expand
    REPLACEMENT['æ'] = "ae";
}

public String convertWord(String word) {
    StringBuilder sb = new StringBuilder(word.length());
    for(int i=0;i<word.length();i++)
        sb.append(REPLACEMENT[word.charAt(i)]);
    return sb.toString();
} 

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