Iterating over string. Searching for special characters. Using regular expressions

Question

My goal is to iterate over a string and pull out instances of certain characters.

Ideally I would want to use Pattern and Matcher.

For example.

String str = "10+10+10";

How would I go about if I wanted to make a code that would detect if the part of the string is a number or the + operator and in turn, save that part of the string in an array depending on what it is and then consequently move on to the next character?

I am aware of that I am supposed to be using regular expressions but not exactly how I am supposed to iterate over a string and look for regular expressions from left to right.

Answer 1

From what you have mentioned, I understand that you simply want to separate numbers from the operators, assuming that you have a well constructed input string. In that case, the following code may help:

public class OperatorsAndNumbers{
    static List<String> parts = new ArrayList<>();
    public static void main( String[] args ){
        String str = "10+10+10";
        Pattern p = Pattern.compile( "(\\d+)|([+-])" );

        /* Run the loop to match the patterns iteratively. */
        Matcher m = p.matcher( str );
        while( m.find() ) {
            handle( m.group() );
        }

        System.out.println( parts );
    }

    /** Do whatever is to be done with detected group. You may want to add them to separate lists or
     * an operation tree, etc. In this example, it simply adds it a list. */
    private static void handle( String part ){
        parts.add( part );
    }

}