Dot behavior in regex patterns

Question

Pattern p2 = Pattern.compile(\".*\");
Matcher m2 = p2.matcher(\"true\");
System.out.println(m2.matches() + \" [\" + m2.group() + \"]\");

When I use

Answer 1

The dot . is a predefined character class. It matches any character (may or may not match line terminators). If want to define character class that includes a range of values, you can use [].

Answer 2

[] is the character class and most inside it stand for their actual symbol. Dot in this case would just be a dot and not a dot with special meaning in regex.

Answer 3

But I don't understand what is going on when I use this regexpr [.]*. It says me false.

Because inside a character class, the dot loses its special meaning and will match a plain old dot (the . character).

Outside of a character class the dot is a metacharacter that matches any character, excluding newlines (unless you use the Pattern.DOTALL modifier, of course).

Or how to make a class of symbols with any characters without \n and \r.

Use a negated character class:

 Pattern p2 = Pattern.compile("[^\\r\n]*");

[^\r\n] means "match anything that's not a \r or a \n.

Answer 4

.* means any character 0 or more times [.]* means dot character 0 or more times