Java Regex to match "string"

Question

I am creating a lexical from scratch and I am getting into the part of matching (")[\\w]+("). I have this regular expression ^(\")[\\w]+(\")$, but it won't catch the string.

SSCCE:

Map<String, String> lexicalMap = new HashMap<>();
// add all regex to `lexicalMap` via `lexicalMap.put([regex], [tokentype])`

// Tokenize the string format of the syntax to `List<String> tokens`
// List<String> tokens contains ["string", "data", "=", "test"] on the syntax: string data = "test"
for(String element : tokens) {
    for(String regex : lexicalMap.keySet()) {
        if(element.matches(regex))
            System.out.print(lexicalMap.get(regex) + " ");
    }
}
System.out.println();

REGEXs:

identifier = ^[\\w]+$
operator = ^(\\=)$
string = ^(\")[\\w]+(\")$ // THE PROBLEM
keyword = ^(string)$

Here is the case input/ouput I am following:

INPUT:

"test"
""
test
string data = "test"

OUTPUT:

string
string
identifier
keyword identifier operator string

UPDATED: 02/22/2013

Added SSCCE segment.

I guess your tokens should contain: ["string", "data", "=", "\"test\""]``. Note how I stored "test"` — Rohit Jain
– Rohit Jain, Commented Feb 22, 2013 at 14:37
wait wait. \"data\" is not a string. If it would have been like - "\"data\"", then that is a string. And that would be stored like - \"\\\"data\\\"\". You first need to be sure of what all kinds of input you are getting? — Rohit Jain
– Rohit Jain, Commented Feb 22, 2013 at 14:42
You would have to do much more work to make this program work completely. The problem is, a keyword is also a valid identifier. So, it will match two regexes in Map. And I would say, you should not match a keyword with regex. Since keywords in Java are fixed, so better to have a Set of all those keywords, and match against that set. — Rohit Jain
– Rohit Jain, Commented Feb 22, 2013 at 14:52

David B · Accepted Answer · 2013-02-22 15:31:54Z

1

I don't know what happened but after changing the regular expression from ^(\")[\\w]+(\")$ to ^(\")[\\w]*(\")?$ it worked correctly.

answered Feb 22, 2013 at 15:31

David B

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3 Comments

nhahtdh Over a year ago

It is going to break badly with a simple string such as "@" or "Enter a number: "

MikeM Over a year ago

Adding ? to (\") makes the " optional, are you sure that is what you want? \\w+ means one or more word characters, \\w* means zero or more. The brackets in your regex seem pointless, so "^\"\\w*\"$", though it only allows word characters between the quotes.

David B Over a year ago

@MikeM true that making the second " can destroy the string grammar. I just need to have an additional procedure to validate the grammar among the string tokens.

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