Extract numbers from String in Java

Question

Referring to this question here. I have a new Problem. I want to extract the last two appearing numbers (longitude/latitude) from a String.

I use the approach from the referenced answer. A simple example where the error occures can be found here:

public static void main(String[] args) {
    String input = "St. Louis (38.6389, -90.342)"; 

    Pattern p = Pattern.compile("-?[\\d\\.]+");
    Matcher m = p.matcher(input);

    while(m.find()){
        System.out.println(m.group());
    }
}

Console output is as following:

.
38.6389
-90.342

The Problem appears to be the "." in "St. Louis". Can someone help me to solve this issue in a nice way?

Thanks a lot for every answer/comment.

Avinash Raj · Accepted Answer · 2015-03-02 09:43:14Z

3

Change your regex like below,

Pattern p = Pattern.compile("-?\\d+(?:\\.\\d+)?");

(?:\\.\\d+)? at the last would make the decimal part as optional.

answered Mar 2, 2015 at 9:43

Avinash Raj

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2 Comments

amit Over a year ago

This fails to catch .9, which is also a common way to write 0.9, Including in java's syntax

Avinash Raj Over a year ago

then this "-?\\d*(?:\\.\\d+)?", but i think .9 would be written as 0.9

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

[-+]?\\d+(\\.\\d+)?

Use this for floating numbers and integers.

The Problem appears to be the "." in "St. Louis"

Thats because of -?[\\d\\.]+ [] the character class.It can match any character defined inside class.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Mar 2, 2015 at 9:43

vks

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5 Comments

amit Over a year ago

This fails to catch .9, which is also a common way to write 0.9, Including in java's syntax

vks Over a year ago

@amit i guess that should be clarified with OP if he wants it or not

amit Over a year ago

Why wouldn't he? It's a legitimate writing, maybe the OP should also explicitly clarify if he wants to include the digit 5 as well?

vks Over a year ago

@amit because these are longitudes and latitudes.i m not very sure there these numbers can appear or not

amit Over a year ago

If 0.9 can appear, so does .9

asontu · Accepted Answer · 2015-03-02 10:30:31Z

0

A regex like -?\d*(?:\.\d+)? causes the engine to find zero-width matches everywhere. A better approach is to simply use alternation to require that either there is a dot with numbers or one or more numbers after which a dot with more numbers is optional:

-?(?:\.\d+|\d+(?:\.\d+)?)

Regular expression visualization

Debuggex Demo

In Java you need to escape this like so:

Pattern p = Pattern.compile("-?(?:\\.\\d+|\\d+(?:\\.\\d+)?)");

Alternatively, you could add a lookahead that requires that there is at least one number somewhere:

-?(?=\.?\d)\d*(?:\.\d+)?

Regular expression visualization

Debuggex Demo

edited Mar 2, 2015 at 10:30

answered Mar 2, 2015 at 10:24

asontu

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