Regex for extraction of a key value pair

Question

I have a text file. Sample content of that particular text file is like

root(ROOT-0, good-4)nn(management-2, company-1)nsubj(good-4, management-2)

Now i need to separate this and store it in ArrayList. For that i write the following code

public class subject {
public void getsub(String f){
    ArrayList <String>ar=new ArrayList<String>();
    String a="[a-z]([a-z]-[0-9],[a-z]-[0-9])";
    Pattern pattern=Pattern.compile(a);
    Matcher matcher=pattern.matcher(f);
    while(matcher.find()){
        if(matcher.find()){
            ar.add(matcher.group(0));
        }
    }
    System.out.println(ar.size());
    for(int i=0;i<ar.size();i++){
        System.out.println(ar.get(i));
    }



}

}

but arraylist is not getting populated. Why is that so

Mena · Accepted Answer · 2014-01-08 11:31:08Z

You are using unquoted parenthesis in your Pattern.

Unquoted parenthesis imply the definition of a group within your Pattern, for later back-references.

However, here you are trying to match actual parenthesis, so they need to be escaped as such: \\( and \\).

For a rough solution, try this:

String text = "root(ROOT-0, good-4)nn(management-2, company-1)nsubj(good-4, management-2)";
List<String> myPairs = new ArrayList<String>();
Pattern p = Pattern.compile(".+?\\(.+?,.+?\\)");
Matcher m = p.matcher(text);
while (m.find()) {
    myPairs.add(m.group());
}
System.out.println(myPairs);

Output:

[root(ROOT-0, good-4), nn(management-2, company-1), nsubj(good-4, management-2)]

Final note: for an improved solution, I would try and use groups to distinguish between the first part of your Pattern and the actual pair in the parenthesis, so to build a Map<String, ArrayList<String>> as a data object in this case - but this is out of scope for this answer.

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