Value pass to regular expression should have specified character

I am trying to create validation so the value passed should be in format as i expect.

For example values can be 40% or 40GB.

I am trying to use开发者_JAVA百科 the regex

(\\d*\\.?\\d*)([MB|GB|TB|PB|%]?)

Is above regex correct?

No it's wrong.

1. The character class [xyz] is for matching single character. In fact, [MB|GB|TB|PB|%] means matching a single character which is one of M, B, |, G, T, P or %. Grouping should be done with (?:...) not [...].

   ((?:MB|GB|TB|PB|%)?)
   

   Of course it is better to collect the prefixes of the bytes. Also, I think the unit is mandatory, so the ? should be removed:

   ([MGTP]B|%)
   

2. The regex matches an empty substring, so anything would pass, e.g. use

   \d+(?:\.\d+)?
   

   instead.

Together:

(\d+(?:\.\d+)?)([MGTP]B|%)

try this

^\d*([MGTP]B|%)$

DEMO