Splitting strings & Pattern matching in Java

Question

I have a following String:

MYLMFILLAAGCSKMYLLFINNAARPFASSTKAASTVVTPHHSYTSKPHHSTTSHCKSSD

I want to split such a string every time a K or R is encountered, except when followed by a P.

Therefore, I want the following output:

MYLMFILLAAGCSK
MYLLFINNAARPFASSTK
AASTVVTPHHSYTSKPHHSTTSHCK
SSD

At first, I tried using simple .split() function in java but I couldn't get the desired result. Because I really don't know how to mention it in the .split() function not to split if there is a P right after K or R.

I've looked at other similar questions and they suggest to use Pattern matching but I don't know how to use it in this context.

Are they **K**, **P** etc as text? Or did you put them in bold for us to see them? — BackSlash
– BackSlash, Commented Feb 9, 2017 at 11:53
You can check your string manually, e.g. with charAt() if it contains K or R alone and then use substring() and the positions found to split your string. — IQV
– IQV, Commented Feb 9, 2017 at 11:57

Bohemian · Accepted Answer · 2017-02-09 12:04:19Z

6

You can use split:

String[] parts = str.split("(?<=[KR])(?!P)");

Because you want to keep the input you're splitting on, you must use a look behind, which asserts without consuming. There are two look arounds:

(?<=[KR]) means "the previous char is either K or R"
(?!P) means "the next char is not a P"

This regex matches between characters where you want to split.

Some test code:

String str = "MYLMFILLAAGCSKMYLLFINNAARPFASSTKAASTVVTPHHSYTSKPHHSTTSHCKSSD";
Arrays.stream(str.split("(?<=[KR])(?!P)")).forEach(System.out::println);

Output:

MYLMFILLAAGCSK
MYLLFINNAARPFASSTK
AASTVVTPHHSYTSKPHHSTTSHCK
SSD

edited Feb 9, 2017 at 12:04

answered Feb 9, 2017 at 11:58

Bohemian♦

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2 Comments

Shakiba Moshiri Over a year ago

After many many reading about negative lock-ahead assertion I now realize how can that be useful. Thanks :)

Lauren boomer Over a year ago

Thanks @Bohemian, your answer has helped me a lot

Luis Colorado · Accepted Answer · 2017-02-10 10:24:46Z

1

Just try this regexp:

(K)([^P]|$)

and substitute each matching by

\1\n\2

as ilustrated in the following demo. No negative lookahead needed. But you cannot use it with split, as it should eliminate the not P character after the K also.

You can do a first transform like the one above, and then .split("\n"); so it should be:

"MYLMFILLAAGCSKMYLLFINNAARPFASSTKAASTVVTPHHSYTSKPHHSTTSHCKSSDK"
    .subst("(K)([^P]|$)", "\1\n\2").split("\n");

answered Feb 10, 2017 at 10:24

Luis Colorado

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