Question

I have large String variable named text. I want to be able to check if text contains a specified searchString (e.g. “test”) and to return all substrings with windowSize chars before and after the matches.

Example:

String windowSize = 5;
String text = "this is only a simple test. lorem impsum testing everything.";
String searchString = "test";

As a result i want the following output:

mple test. lor
ssum testing e

Additionally, it would be great to be able to have different types of output:

Only before:

mple 
ssum 

Only after:

. lor
ing e

Solution

Thanks to Peter Lawrey and SubmittedDenied i got my answer:

String windowSize = 5;
String text = "this is only a simple test. lorem impsum testing everything.";
String searchString = "test";

int i = -1;
while((i = text.indexOf(searchString, i+1)) > -1) {
    System.out.println(text.substring(Math.max(0, i - windowSize), Math.min(i + searchString.length() + windowSize, text.length())));
}

Answer 1

You can find the location of a substring with the indexOf(string) method, this will also return -1 if there is no such substring.

You’d want to do something like:

String windowSize = 5;
String text = "this is only a simple test. lorem impsum testing everything.";
String searchString = "test";
int i = -1;
while((i = text.indexOf(test, i + 1)) > -1)
{
    System.out.println(text.substring(i - windowSize, i + searchString.length() + windowSize));
}

You’ll probably need to catch errors like if the first occurence of test is less than windowSize characters into the string.