Regular expressions simplify pattern-matching code - 12

 java RegexDemo a+ abaa: uses a greedy quantifier to match a in abaa one or more times. The following output results:

Regex = a+

Text = abaa

Found a

  starting at index 0 and ending at index 1

Found aa

  starting at index 2 and ending at index 4

The output reveals two matches. Unlike a? and a*, a+ does not match the absence of a. Thus, no zero-length matches result. Like a*, a+ matches all consecutive as.

2. java RegexDemo a{2} aababbaaaab: uses a greedy quantifier to match every aa sequence in aababbaaaab. The following output results:

Regex = a{2}

Text = aababbaaaab

Found aa

  starting at index 0 and ending at index 2

Found aa

  starting at index 6 and ending at index 8

Found aa

  starting at index 8 and ending at index 10

3. java RegexDemo a{2,} aababbaaaab: uses a greedy quantifier to match two or more consecutive as in aababbaaaab. The following output results:

Regex = a{2,}

Text = aababbaaaab

Found aa

  starting at index 0 and ending at index 2

Found aaaa

  starting at index 6 and ending at index 10

4. java RegexDemo a{1,3} aababbaaaab: uses a greedy quantifier to match every a, aa, or aaa in aababbaaaab. The following output results:

Regex = a{1,3}

Text = aababbaaaab

Found aa

  starting at index 0 and ending at index 2

Found a

  starting at index 3 and ending at index 4

Found aaa

  starting at index 6 and ending at index 9

Found a

  starting at index 9 and ending at index 10

5. java RegexDemo a+? abaa: uses a reluctant quantifier to match a in abaa one or more times. The following output results:

Regex = a+?

Text = abaa

Found a

  starting at index 0 and ending at index 1

Found a

  starting at index 2 and ending at index 3

Found a

  starting at index 3 and ending at index 4

Unlike its greedy variant in the third example, the reluctant example produces three matches of a single a because the reluctant quantifier tries to find the shortest match.