Question

A string will be made up of certain symbols (ax,bx,dx,c,acc for example) and numbers.

ex: ax 5 5 dx 3 acc c ax bx

I want to replace one or all of the symbols (randomly) with another symbol of the same set. ie, replace one of {ax,bx,dx,c,acc} with one of {ax,bx,dx,c,acc}.

replacement example: acc 5 5 dx 3 acc c ax bx or c 5 5 dx 3 acc c ax ax

Is there a way to do this with regexes? In Java? If so, which methods should I use?

Answer 1

I think this is the most clean solution for replacing a certain set of symbols from a string containing a superset of them. appendreplacement is the key to this method. one important caveat: do not include any unescped dollar characters ($) in your elements list. escape them by using ‘\$’ eventually use
.replaceall(‘\$’,’\\$’); on every string before adding it to the list. see also the javadoc in doubt about the $ signs.

import java.util.*; import java.util.regex.Pattern; import java.util.regex.Matcher;  public class ReplaceTokens { public static void main(String[] args) {     List<String> elements = Arrays.asList('ax', 'bx', 'dx', 'c', 'acc');     final String patternStr = join(elements, '|'); //build string 'ax|bx|dx|c|acc'      Pattern p = Pattern.compile(patternStr);     Matcher m = p.matcher('ax 5 5 dx 3 acc c ax bx');     StringBuffer sb = new StringBuffer();     Random rand = new Random();     while (m.find()){         String randomSymbol = elements.get(rand.nextInt(elements.size()));         m.appendReplacement(sb,randomSymbol);     }     m.appendTail(sb);     System.out.println(sb); }  /**  * this method is only needed to generate the string ax|bx|dx|c|acc in a clean way....  * @see org.apache.commons.lang.StringUtils.join    for a more common alternative...  */ public static String join(List<String> s, String delimiter) {     if (s.isEmpty()) return '';     Iterator<String> iter = s.iterator();     StringBuffer buffer = new StringBuffer(iter.next());     while (iter.hasNext()) buffer.append(delimiter).append(iter.next());     return buffer.toString(); }