java - regex pattern is matching with one of the pattern i cant able to follow? -

i come across regex pattern , matching pattern strings, confused 1 of matched pattern

target: .50 1.50 0.50 10.50 00.50 1.555  pattern: (0|[1-9]\d*)\.\d\d  matches with: (4,7:1.50)(9,12:0.50)(14,18:10.50)(21,24:0.50)(26,29:1.55) 

what deduce pattern 2 digit after decimal, , before decimal group in first digit either 0 or digit between 1 9, followed empty string or number string...

i think in last second match should 00.50.

what missing??

i think in last second match should 00.50.

what missing??

no, part of regex (0|[1-9]\d*)\. can rewritten (0\.|[1-9]\d*\.), can accept

• one 0 , .

or

• [1-9]\d* , .

if want allow many zeroes before dot use

(0+|[1-9]\d*)\.\d\d   ^--one or more zeroes