检查字符串是否为长度为 1 到 5 的字母数字

Question

I have wrote the following test code snippet:

"123".matches("\\[a-zA-Z0-9]{1,5}");

However, it returns false .

Why and how to fix this?

Answer 1

By escaping the first [ , you made it a literal [ , while you wanted to define a character class (bracket expression).

Remove \\ :

"123".matches("[a-zA-Z0-9]{1,5}");
               ^  

See the Java demo :

System.out.println("123".matches("[a-zA-Z0-9]{1,5}")); // = > true

Answer 2

Regex without \\\\ will work. You don't need to escape anything.

"123".matches("[a-zA-Z0-9]{1,5}");

Answer 3

You're escaping the first square bracket with the \\\\ , which means the expression between the square brackets isn't treated as a character class. Remove the escaping and you should be OK:

"123".matches("[a-zA-Z0-9]{1,5}"
// Here -------^