Presentación y duda sobre programa en java

public class Replace {

        public static String replace(String str, String search, String replace) {
                return str.replaceAll(search, replace);
        }

        public static void main(String[] args) {

                String sURL = "http://www.google.com";
                String new_URL = replace(sURL,"http://","[");
                System.out.println(new_URL+ "]");

        }

}

    String Link = "(https?)://(www\\d?|[a-zA-Z0-9]+)?.[a-zA-Z0-9-]+(\\:|.)([a-zA-Z0-9.]+|(\\d+)?)([/?:].*)?";
        
       Pattern patternLink = Pattern.compile(Link);
       Matcher matcherLink = patternLink.matcher(s);
        
       if (matcherLink.find()){
    	   LinkSearch=matcherLink.group();
           String LinkSearch_replace= replace(LinkSearch,"http://","[");
    	   return LinkSearch_replace; 

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


public class EjercicioRegex {
    
    public static void main(String []args){
    String textoaextraer="[url=http://alkuytem.com/up//uploads/images/alkuytem-com-d77a9995a4.jpeg][img]http://alkuytem.com/up//uploads/images/alkuytem-com-d77a9995a4.jpeg[/img][/url]";
    String pattern = "\\[url\\=(.+?)\\]\\[img\\](.*?)\\[\\/img\\]\\[\\/url\\]";
    Pattern p = Pattern.compile(pattern);
    Matcher m = p.matcher(textoaextraer);
    if (m.find()){
    System.out.println(m.group(0));
    System.out.println(m.group(1));
            System.out.println(m.group(2));
            System.out.println("["  + m.group(2) + "]"); //Este es el ejemplo que te interesa
            
    }
    else {
            System.out.println("Matchers not found");
            
            }
  
    }
    
}

package org.underc0de.regextest;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 *
 * @author Gustavo
 */
public class RegexLinkEditor {

    private final String REGEX = "(https?)://";
    private final String FILE_PATH = "D://links.txt";
    private final List<String> newLines = new ArrayList<>();
    private boolean hasLinks;
    
    public void run() throws IOException {
        boolean exists = IOUtils.exists(FILE_PATH);
        if (exists) {
            evaluate();
        } else {
            System.out.println("I'm sorry. The request file was not found.");
            System.exit(-1);
        }
    }

    /*
     * Si el archivo tená links, se escriben en el archivo
     * los links con el nuevo formato: [www.xyz.com]
    */
    private void evaluate() throws IOException {
        execute();
        if (hasLinks) {
            IOUtils.writeLines(newLines, FILE_PATH);
        } else {
            System.out.println("Not links found");
        }
    }

    private List<String> execute() throws IOException {
        List<String> oldLines = IOUtils.getAllLinesOf(FILE_PATH);
        Pattern pattern = Pattern.compile(REGEX);
        
        oldLines.stream().map((current) -> {
            Matcher matcher = pattern.matcher(current);
            String newLine = current;
            if (matcher.find()) {
                if(hasLinks == false) hasLinks = true; // cambia la bandera indicando que hay links
                newLine = replace(current);
            }
            return newLine;
        }).forEach((newLine) -> {
            newLines.add(newLine);
        });

        return newLines;
    }

    private String replace(String line) {
        String newLine = line.replaceAll(REGEX, "[") + "]";
        return newLine;
    }
}

package org.underc0de.regextest;

import java.io.BufferedWriter;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

/**
 *
 * @author Gustavo
 */
public class IOUtils {

    public static boolean exists(String path) {
        return new File(path).exists();
    }

    public static List<String> getAllLinesOf(String path) {
        List<String> lines = new ArrayList<>();
        try {
            lines =  Files.readAllLines(Paths.get(path), Charset.forName("UTF-8"));
        } catch (IOException e) {
            ExceptionUtils.showException(e);
        }
        return lines;
    }

    public static void writeLines(List<String> lines, String path) {
        try (BufferedWriter bw = new BufferedWriter
            (new PrintWriter(path))) {
            for(String line : lines) {
                bw.write(line);
                bw.newLine();
                bw.flush();
            }
        } catch(IOException e) {
            ExceptionUtils.showException(e);
        }
    }
}

package org.underc0de.regextest;

import java.io.PrintWriter;
import java.io.StringWriter;

/**
 *
 * @author Gustavo
 */
public class ExceptionUtils {

    public static void showException(Exception e) {
        StringWriter sw = new StringWriter();
        PrintWriter pw = new PrintWriter(sw);
        e.printStackTrace(pw);
        String exceptionText = sw.toString();
        System.out.println(exceptionText);
    }
}

/*
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 * and open the template in the editor.
 */
package org.underc0de.regextest;

import java.io.IOException;

/**
 *
 * @author Gustavo
 */
public class Main {
    public static void main(String[] args) {
        try {
            RegexLinkEditor editor = new RegexLinkEditor();
            editor.run();
        } catch (IOException e) {
            ExceptionUtils.showException(e);
        }
    }
}