CODEWITHSUNDEEP
javaregex
mr jorden
mr jorden

Reputation: 89

Pattern and Matcher is not working in java

Basically I have a simple String Where I need to explicitly restrict characters other than a-zA-Z0-9. Before I mention what is wrong here is how I am doing it.

Pattern p = Pattern.compile("[&=]");
Matcher m = p.matcher("Nothing is wrong");
if (m.find()){
    out.print("You are not allowed to have &=.");
    return;
}

Pattern p1 = Pattern.compile("[a-zA-Z0-9]");
Matcher m1 = p1.matcher("Itissupposetobeworking");
if (m1.find()){
    out.print("There is something wrong.");
    return;
}

The first one works fine, But on the second matcher m1 always gets to execute if(m1.find()) even though it doesn't contain any character other than specified in the pattern.

I also tried Pattern p1 = Pattern.compile("[abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789]") But still have the same trouble.

and if you might wanna tell, which is better between String.matches(["a-zA-Z0-9"]); or the way I am using above?

Thanks in advance.

Upvotes: 1

Views: 1023

Answers (4)

Dark Army
Dark Army

Reputation: 268

When above expression finds a matching it prints "There is something wrong." but if you want to restrict then Use below code.

    Pattern p1 = Pattern.compile("a-zA-Z0-9");
    String a = "It$issupposetobeworking";
    Matcher m1 = p1.matcher(a);
    if (m1.find()){
        System.out.print("There is something wrong.");
    }
    else
    {
        System.out.println("Everything is fine");
    }

If you want the same code to be working with same regular expression in that scenario use this code.

    Pattern p1 = Pattern.compile("[a-zA-Z0-9]");
    Matcher m1 = p1.matcher("Itissupposetobeworking");
    if (!(m1.find())){
           out.print("There is something wrong.");
            return;
     }

Upvotes: 1

Manuel Drieschmanns
Manuel Drieschmanns

Reputation: 744

If you use the isAlphanumeric Method of org.apache.commons.lang.StringUtils yourcode become much more readable. So you need to write

if (!StringUtils.isAlphanumeric("Itissupposetobeworking"))

instead of

Pattern p1 = Pattern.compile("[a-zA-Z0-9]");
Matcher m1 = p1.matcher("Itissupposetobeworking");
if (!m1.find()){

Upvotes: 1

Sunil Reddy
Sunil Reddy

Reputation: 78

[a-zA-Z0-9] tries to match alphanumeric characters.

So, you will get "There is something wrong." to be printed, if you have a alphanumeric character in the input character sequence of matcher().

Change it to [^a-zA-Z0-9] and try.

This tries to match non-alphanumeric characters. So, you will get expected result.

Upvotes: 2

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 627517

You seem to want to find a partial match in a string that contains a character other than an alphanumeric character: 

Pattern p1 = Pattern.compile("[^a-zA-Z0-9]");

or

Pattern p1 = Pattern.compile("\\P{Alnum}");

The [^a-zA-Z0-9] pattern is a negated character class that matches any char other than the ones defined in the class. So, if a string contains any chars other than ASCII letters or digits, your if (m1.find()) will get triggered and the message will appear.

Note that the whole negated character class can be replaced with a predefined character class \P{Alnum} that matches any char other than alphanumeric. \p{Alnum} matches any alphanumeric character and \P{Alnum} is the reverse class.

Upvotes: 1

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