Can someone explain how this regex works? The case was:"You must enter at least at 6 characters, and no space, including special characters!"

matches(^(?=.*\\W)(?=.*[a-zA-Z])(?!.*\\s).{6,}$);

CodePudding user response：

(?=...) is a positive lookahead assertion, and it tests whether the expression ... matches anything immediately ahead of the current position

(?!...) is a negative lookahead assertion, and it tests whether the expression ... does NOT match the text immediately ahead of the current position

• \W means "non-word", eg any character that's not a digit, letter or underscore.
• [a-zA-Z] means any letter a through z or A through Z (eg. letters of the english/latin alphabet)
• \s means "whitespace"

So :

• (?=.*\\W) ensure at least 1 non-word character occurs
• (?=.*[a-zA-Z]) ensures at least 1 letter occurs
• (?!.*\\s) ensure no whitespace occurs
• .{6,} will only match if the string is at least 6 characters long (because there won't be any 6-character-or-longer substring to match against at the start of the string if the total length of the string is any shorter)