How to use regex with String.matches in java

Question

I have a String array

String[] arrayOfLine = {
    "I.2 Other Interpretive Provisions",
    "I.3 Accounting Terms",
    "Including all",
    "II.1 The Loans",
    "II.3 Prepayments.",
    "III.2 Illegality",
    "IV.2 Conditions",
    "V.2 Authorization",
    "expected to have"
};

I want to pick only those array elements which starts with roman.number i.e starting with I.2, II.1 and so on.

I am trying this, but it is not working

String regex = "\b[A-Z]+\\.[0-9]\b";
for (int i = 0; i < arrayOfLine.length; i++) {
    if(arrayOfLine[i].matches(regex)){
        listOfHeadings.add(arrayOfLine[i]);
    }
}

\b must be \\b. Also, you need to use .find() with a Matcher object. It looks like you need to find all items that start with the pattern. If yes, use ^[A-Z]+\\.[0-9] — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jul 31, 2017 at 11:01
.matches will attempt to match complete input. Use: "[A-Z]+\\.[0-9]\\b.*" — anubhava
– anubhava, Commented Jul 31, 2017 at 11:02
The example you gave for arrayOfLine, can it contain values other than you mentioned ? — Anup Kumar Gupta
– Anup Kumar Gupta, Commented Jul 31, 2017 at 11:15

Wiktor Stribiżew · Accepted Answer · 2017-07-31 11:06:38Z

7

It looks like you need to find all items that start with the pattern. Use "^[A-Z]+\\.[0-9]+\\b" pattern and make sure you run the find() method of the Matcher object to find partial matches inside strings. .matches() finds the entire string matches only. Note that \b word boundary must be defined as "\\b" inside a Java string literal.

See the Java demo

String[] arrayOfLine = {"I.2 Other Interpretive Provisions" , "I.3 Accounting Terms","Including all","II.1 The Loans","II.3 Prepayments.","III.2 Illegality","IV.2 Conditions","V.2 Authorization","expected to have"};
Pattern pat = Pattern.compile("^[A-Z]+\\.[0-9]+\\b");
List<String> listOfHeadings = new ArrayList<>();
for (String s : arrayOfLine) {
    Matcher m = pat.matcher(s);
    if (m.find()) {
        listOfHeadings.add(s);
    }
}
System.out.println(listOfHeadings);

answered Jul 31, 2017 at 11:06

Wiktor Stribiżew

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2 Comments

jagga Over a year ago

if i add "2017 ." , "." , "$30","AVAILABLE.”" in arrayOfLine than these are also picked up by pattern.

Wiktor Stribiżew Over a year ago

@jagga: Please show me your code. My solution does not find them.

Symph · Accepted Answer · 2017-07-31 11:16:42Z

0

You sould try using Patterns and Matchers. Here is a working example

    Pattern pattern = Pattern.compile("[A-Z]+\\.[0-9]");
    for (int i = 0; i < arrayOfLine.length; i++) {
        Matcher match = pattern.matcher(arrayOfLine[i]);
        while (match.find()) {
            listOfHeadings.add(match.group());
        }
    }

answered Jul 31, 2017 at 11:16

Symph

368 bronze badges

Comments

Rohit-Pandey · Accepted Answer · 2017-08-04 17:49:20Z

Here is regex for checking roman number with dot is ^M{0,4}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})[.].

import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
class test
    {
     public static void main(String[] args) {
     String[] a = {
     "I.2 Other Interpretive Provisions",
     "I.3 Accounting Terms",
     "Including all",
     "II.1 The Loans",
     "II.3 Prepayments.",
     "III.2 Illegality",
     "IV.2 Conditions",
     "V.2 Authorization",
     "expected to have"
     };
     int i=0;
     int b=a.length;
     Pattern MY_PATTERN = Pattern.compile("^M{0,4}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})[.]");
     for(i=0;i<b;i++)
     {
         Matcher m = MY_PATTERN.matcher(a[i]);
         if (m.find())
             System.out.println(a[i]);
     }
     }
 }

Output:

I.2 Other Interpretive Provisions
I.3 Accounting Terms
II.1 The Loans
II.3 Prepayments.
III.2 Illegality
IV.2 Conditions
V.2 Authorization

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