为什么string.replaceAll行为异常

Question

I have always used string.replaceAll() without any problems.

But now I'm just stumped...

Here is my code

public static String getVersionName() {
    String versionName = null;
    versionName = "v"+packageInfo.versionName;
    versionName = versionName.replaceAll(".","_");
    return versionName;
}

versionName before replaceAll is v1.0.4

expected result is v1_0_4 actual result is either v____ or _____ it varies for some reason, and is never the expected result.

Why is this happening? How can I fix it?

Answer 1

It's happening because replaceAll uses regular expressions.

You need to escape the "." using "\\\\."

Answer 2

It's happening because replaceAll expects a regex. You should probably use replace instead (which still replaces all occurences), since you only want to match a single character.

So using versionName = versionName.replace('.','_'); on v1.0.4 will give you v1_0_4 as a result.

Answer 3

replaceAll() uses regular expressions, within which . matches any character .

Your options are to escape the . so it just means "." again, using \\\\.

Or, if you don't need regular expressions (You don't in this case), you should use replace() instead, which will be faster and you won't now have two problems to solve .

versionName = versionName.replace(".","_");