Replacer.java

import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Replacer {

	public static void main(String[] args) {
		Replacer replacer = new Replacer();
		replacer.addReplacement(Replacer.NUMBER, numberString -> "(" + numberString + ")");

		System.out.println(
				replacer.replace("ovo je neki broj 1.4213 a ovo je neki drugi -123e10")
		);
	}

	/**
	 * Regular expression for finding numbers in double format
	 */
	public static final String NUMBER = "[-+]?[0-9]*\\.?[0-9]+([eE][-+]?[0-9]+)?";

	private Map<Pattern, Function<String, String>> replacers = new HashMap<>();

	public void addReplacement(String regex, Function<String, String> replacer) {
		replacers.put(Pattern.compile(regex), replacer);
	}

	public String replace(String s) {

		StringBuffer buffer = new StringBuffer();

		for (Map.Entry<Pattern, Function<String, String>> e : replacers.entrySet()) {
			buffer.setLength(0); // empty
			Matcher m = e.getKey().matcher(s);
			while (m.find()) {
				m.appendReplacement(buffer, e.getValue().apply(m.group()));
			}
			m.appendTail(buffer);
			s = buffer.toString();
		}

		return s;
	}

}