Extract values from string using regex groups

Question

I have to extract values from string using regex groups.

Inputs are like this,

-> 1
-> 5.2
-> 1(2)
-> 3(*)
-> 2(3).2
-> 1(*).5

Now I write following code for getting values from these inputs.

String stringToSearch = "2(3).2";
Pattern p = Pattern.compile("(\\d+)(\\.|\\()(\\d+|\\*)\\)(\\.)(\\d+)");
Matcher m = p.matcher(stringToSearch);

System.out.println("1: "+m.group(1)); // O/P: 2
System.out.println("3: "+m.group(3)); // O/P: 3
System.out.println("3: "+m.group(5)); // O/P: 2

But, my problem is only first group is compulsory and others are optional.

Thats why I need regex like, It will check all patterns and extract values.

What about using the ? qualifier to make those groups optional? (Might be totally missing what you are asking) — Andy Turner
– Andy Turner, Commented Jan 23, 2015 at 11:40
@Andy I tried also that but, It gives null values for groups.... — Sheel
– Sheel, Commented Jan 23, 2015 at 11:41

Avinash Raj · Accepted Answer · 2015-01-23 12:16:29Z

2

Use non-capturing groups and turn them to optional by adding ? quantifier next to those groups.

^(\d+)(?:\((\d+|\*)\))?(?:\.(\d+))?$

DEMO

Java regex would be,

"(?m)^(\\d+)(?:\\((\d\+|\\*)\\))?(?:\\.(\\d+))?$"

Example:

String input = "1\n" + 
        "5.2\n" + 
        "1(2)\n" + 
        "3(*)\n" + 
        "2(3).2\n" + 
        "1(*).5";
Matcher m = Pattern.compile("(?m)^(\\d+)(?:\\((\\d+|\\*)\\))?(?:\\.(\\d+))?$").matcher(input);
while(m.find())
{
    if (m.group(1) != null)
    System.out.println(m.group(1));
    if (m.group(2) != null)
    System.out.println(m.group(2));
    if (m.group(3) != null)
    System.out.println(m.group(3));
}

edited Jan 23, 2015 at 12:16

answered Jan 23, 2015 at 11:42

Avinash Raj

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2 Comments

Sheel Over a year ago

It gives "Invalid escape sequence" in java

Avinash Raj Over a year ago

it works for me. Check the update.. You need to escape the backslash one more time.

anubhava · Accepted Answer · 2015-01-23 11:47:43Z

1

Here is an alternate approach that is simpler to understand.

First replace all non-digit, non-* characters by a colon
Split by :

Code:

String repl = input.replaceAll("[^\\d*]+", ":");
String[] tok = repl.split(":");

RegEx Demo

answered Jan 23, 2015 at 11:47

anubhava

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