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Groups Usage (Pattern & Matcher )

 
Krishna Mir
Greenhorn
Posts: 12
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When regular expressions are used as patterns to match the input strings, it results in groups of strings that have matched the pattern. These groups can be accessed using a back reference \n where n is the index of the group captured. I didn't understand the following table.


Whole content Regular expression Result

abab ([a-z][a-z])\1 Found the text "abab" starting at
index 0 and ending at index 4.

abcd ([a-z][a-z])\1 No match found

abcd ([a-z][a-z]) Found the text "ab" starting at
index 0 and ending at index 2.
and the text "cd" starting at
index 2 and ending at index 4

Can anybody please help me to undetstand above?

Thanks
 
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