BackReferences

package exercise;

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

public class BackReferences {
    public static void main(String[] args) {
        String input = "One:two:three:four";
        String regexe = "(\\w+):(\\w+):(\\w+):(\\w+)"; // pattern to be matched
        String replacement = "$4-$3-$2-$1";    // replacement pattern with back references

        // Step 1: Allocate a Pattern object to compile a regexe
        Pattern pattern = Pattern.compile(regexe);

        // Step 2: Allocate a Matcher object from the Pattern, and provide the input
        Matcher matcher = pattern.matcher(input);

        // Step 3: Perform the matching and process the matching result
        String output = matcher.replaceAll(replacement);     // all matches
        //String output = matcher.replaceFirst(replacement); // first match only
        System.out.println(output);
    }
}