替换前导零

Question

Given a String containing this:

Count     %
===========
00000  000%
00012  001%
00905  099%

I want it to look like this:

Count     %
===========
    0    0%
   12    1%
  905   99%

The closest I could get is this:

Count     %
===========
    %
 12   1%
 905   99%

Using this code:

strv.replaceAll("\\b0+", " ")

Answer 1

Since you want the space to be maintained as-is, it is important that each 0 is matched individually and then replaced with a space: ' '. Take a look at this regex:

(?<=\b|\G)0(?=\d)

• (?<=\\b|\\G) is a positive lookbehind which ensures that the matching 0 is preceeded by either \\b or \\G
  • \\b represents a word boundary which means \\b0 will help match the first zero
  • \\G helps assert the position at the end of the previous match (which will be after the previous zero). So it will help match the next zero and so on. Thus forming a continuous chain of 0 's only.
  • Note that since the chain starts with \\b , there is no way it can be formed for 10000 because the word boundary \\b is before 1 and not 0
• Finally a positive lookahead (?=\\d) also needs to be added because if an input contains only zero's then we need to leave one zero behind. This positive lookahead tells the engine to match all zeros which are followed by a number . So, if input is 0000 , then regex will match first 3 0 's because last one isn't followed by a digit .

Usage

strv.replaceAll("(?<=\\b|\\G)0(?=\\d)", " ")

Regex101 Demo

EDIT: Updating as per @SebastianProske's suggestions. Thanks!