Replacing one character in string with another string excluding pattern

Question

I need to replace all '%' characters in string with "%25" but I don't want to replace % in %25 to avoid situation, when I get something like this %%25. I want to do it in Java. Example: input: % sdfsdaf %25 expected result: %25 sdfsdaf %25

Do you know what should I use to get it?

See [HTTP URL Address Encoding in Java](http://stackoverflow.com/questions/724043/http-url-address-encoding-in-java). — Wiktor Stribiżew, Mar 13 '17 at 11:53
Welcome to Stackoverflow. In order to ask propery questions you need to show what you have done and what errors you have found. Check the [help](http://stackoverflow.com/help/mcve) to know how to provide a mcve — Rene Hernandez, Mar 13 '17 at 11:54

score 1 · Accepted Answer · answered Mar 13 '17 at 12:02

Without discussing much and digging deep into what you are really trying to accomplish with the replacement ... the answer to your question could be something like :

myString.replaceAll("%(?!25)", "%25");

From Pattern Documentation ; The (?!...) part means "only match if the text following (hence: lookahead) this doesn't (hence: negative) match this. But it doesn't actually consume the characters it matches (hence: zero-width).

Section 3.5 of the Link clarifies it in a bit more detail.

Replacing one character in string with another string excluding pattern

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