How to Extract Text After a Regex Match Using Lookbehind Assertions?

Retrieving Text after Regex Match

In your quest to use Regex effectively, you've encountered a challenge: extracting text following a matched pattern. Let's delve into the solution.

Your original Regex pattern, "sentence(.*)", nearly accomplishes your goal. However, it indiscriminately captures both the matched string ("sentence") and the subsequent text. To amend this, we need to introduce a concept known as a "lookbehind assertion."

Using a Lookbehind Assertion

A positive lookbehind assertion (?<=...) matches a specific position in the string, immediately after a given expression. In this case, we want to match a position right after the string "sentence":

(?<=sentence).*

This pattern reads as "Match zero or more characters after a position where 'sentence' immediately precedes it." Thus, it successfully extracts the desired text.

Implementing in Java

To implement this in Java, you can modify your code as follows:

Pattern pattern = Pattern.compile("(?<=sentence).*");

Matcher matcher = pattern.matcher("some lame sentence that is awesome");

boolean found = false;
while (matcher.find()) {
    System.out.println("I found the text: " + matcher.group().toString());
    found = true;
}
if (!found) {
    System.out.println("I didn't find the text");
}

Now, when the Regex is applied to the input string, it will only match and print the text following "sentence":

I found the text: that is awesome

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