用Java分割字符串和模式匹配

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.

Answer 1

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

Answer 2

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");