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Editorial Team
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Asked: 2026-05-20T05:01:48+00:00

What is the fastest way to do a search and replace on a string

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What is the fastest way to do a search and replace on a string in an existing file using Java?

Let’s say I have this:

// This references an existing file 
File file = ...

The file in question looks like this:

The Green Dog is furry.
It likes to run in the Green Grass.
Green is its favorite color.

How would I go about replacing the String “Green” with “Blue” and having that file re-saved with the new color?

Update:
I’ve thought about this a little more and perhaps the best and fastest way is to just read the contents of the file into a string (using something like FileUtils) and then just doing a replace and re-writing to the file?

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1 Answer

  1. Editorial Team

    Have a look at Retrieving and Replacing number in text file which is pretty much the same.

    Edit: Regarding your update, I would just use BufferedReader and BufferedWriter and leave it to the JVM to optimise reads/writes, i.e. I would do the replacements in a streaming fashion. Your suggested solution of reading to memory could be a bit faster – but I wouldn’t read everything in memory (makes approach not scalable) unless there’s a very good reason.

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