regex example in java

Question

i want to get an input from user in string type and find the first 2 numbers and multiply them and replace the result in text the user should put the command word first , the command is : mul example : mul hello 2 car ?7color 9goodbye5 the result should be : 14color 9goodbye5 i wrote this code but its not working can you help me for solving the problem?

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Collusion {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String input = scanner.nextLine();

        String patternString = "((\\d+).+(\\d+))";
        Pattern pattern = Pattern.compile(patternString);
        Matcher matcher = pattern.matcher(input);

        String text = matcher.group(0);
        String found = matcher.group(1);
        String thirdGroup = matcher.group(2);
        String fourthGroup = matcher.group(3);

        int firstNum = Integer.parseInt(thirdGroup);
        int secondNum = Integer.parseInt(fourthGroup);

        int integerMultiple = firstNum * secondNum ;
        String multiple = String.valueOf(integerMultiple);

        while (matcher.find()) {
            String result = text.replace(multiple , found);
            System.out.println(result );

            }
        }
    }

i wrote this code but its not working Can you be more specific? — AMC
– AMC, Commented Mar 9, 2020 at 18:57
"It doesn't work" is not a valid problem statement. Read ericlippert.com/2014/03/05/how-to-debug-small-programs — Robert Harvey
– Robert Harvey, Commented Mar 9, 2020 at 19:01

Arvind Kumar Avinash · Accepted Answer · 2020-03-09 19:41:30Z

Do it as follows:

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Collusion {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the command: ");
        String input = scanner.nextLine();
        Pattern p = Pattern.compile("\\d+");
        Matcher m = p.matcher(input);
        int count = 0, product = 1, index = 0;
        while (m.find() && count != 2) {
            product *= Integer.parseInt(m.group());
            count++;
            if (count == 2) {
                index = m.start() + m.group().length();
            }
        }
        System.out.println(product + input.substring(index));
    }
}

A sample run:

Enter the command: mul hello 2 car ?7color 9goodbye5
14color 9goodbye5

I also recommend you go through an elegant regex Test Harness program by Oracle to learn more about the effective usage of java.util.regex.Matcher.

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