正则表达式允许特殊字符

Question

I am using the following pattern to match my String:

[a-zA-Z0-9]*

Even when I am passing the String *$# , its getting matched by the regular expression. Could someone explain what am I doing wrong or why this is happening?

Answer 1

You should use ^ (start of the string) and $ (end of the string).

So,the regex would be

^[a-zA-Z0-9]*$

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[a-zA-Z0-9]* would match anywhere in the string if you use find method..Using ^ and $ would match the entire input from start till end

if you use matches method you don't need to have ^ , $ as it tries to match the entire string

Answer 2

[a-zA-Z0-9]* means 0 or more of any of those characters. If you're using Matcher.find() , it'll find that anywhere/everywhere because it can match anywhere in a string.