Check validation of the Regex

Hi

Is there any way to make sure that a certain regex is valid ?

I give textfield with regex for user, but if user is filling "*" for example the program crash.

Hi
Check like this.I have demonstrated with the small piece of code.Just it checks the text for "*".if it finds then it prints invalid else valid.

Go thru the below link for better understanding.
Pattern (Java 2 Platform SE v1.4.2))

import java.util.regex.*;
class LogIn
{
public static void main(String args[])
{

String input = "sun*com";
//Checks for the string which is having * or not
Pattern p = Pattern.compile("\\*");
Matcher m = p.matcher(input);
if (m.find())
System.err.println("invalid string.");
else
System.err.println("valid string");

//Checks for email addresses that start with
//www. and prints a message if it does.

}//main
}//class

Sorry but you miss-understand me

I have text , tested text, let call it.

I also have a regex string , which the user provides.
if the text is

Quote:

---

abc1234

---

and the user put in the regex

Quote:

---

abc[/d]*

---

then we have a match
but if user put in regex

Quote:

---

abcd+

---

- no match.

The problem is what the user put "bad regex" ?

Quote:

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*abc*

---

which is one example , and I'm sure there are more. ( the * in the begining makes it "bad" regex )
on the function

Code:

---

text.matches(regexStr);

---

I get these errors:

Quote:

---

Exception in thread "AWT-EventQueue-0" java.util.regex.PatternSyntaxException: Dangling meta character '*' near index 0
*[dD]*
^
at java.util.regex.Pattern.error(Pattern.java:1650)
at java.util.regex.Pattern.sequence(Pattern.java:1787 )
at java.util.regex.Pattern.expr(Pattern.java:1687)
at java.util.regex.Pattern.compile(Pattern.java:1397)
at java.util.regex.Pattern.<init>(Pattern.java:1124)
at java.util.regex.Pattern.compile(Pattern.java:817)
at java.util.regex.Pattern.matches(Pattern.java:919)
at java.lang.String.matches(String.java:1921)

---

Looking through java.util.regex I couldn't find anything which tested if the regular expression was well formed. The only suggestion I can give is to use a try-catch.

That does seem like it would be a useful method to incorporate into the Pattern class.

Mr. Beans

nice, try-catch seem to be the simplest solution. thanks

How can I marked this topic as "Solved" ?