Regular expression for string with apostrophes

Question

I'm trying to build regex which will filter form string all non-alphabetical characters, and if any string contains single quotes then I want to keep it as an exception to the rule.

So for example when I enter

car's34

as a result I want to get

car's

when I enter

*&* Lisa's car 0)*

I want to get

Lisa's

at the moment I use this:

string.replaceAll("[^A-Za-z]", "")

however, it gives me only alphabets, and removed the desired single quotas.

Answer 1

This will also remove apostrophes that are not "part if words":

string = string.replaceAll("[^A-Za-z' ]+|(?<=^|\\W)'|'(?=\\W|$)", "")
    .replaceAll(" +", " ").trim();

This first simply adds an apostrophe to the list of chars you want to keep, but uses look arounds to find apostrophes not within words, so

I'm a ' 123 & 'test'

would become

I'm a test

Note how the solitary apostrophe was removed, as well as the apostrophes wrapping test, but I'm was preserved.

---

The subsequent replaceAll() is to replace multiple spaces with a single space, which will result if there's a solitary apostrophe in the input. A further call to trim() was added in case it occurs at the end of the input.

Here's a test:

String string = "I'm a ' 123 & 'test'";
string = string.replaceAll("[^A-Za-z' ]+|(?<=^|\\W)'|'(?=\\W|$)", "").replaceAll(" +", " ").trim();
System.out.println(string);

Output:

I'm a test