This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
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