code: public void addAll(String prefix, String[] strings) {
  		if (strings == null) {
  			return;
  		}
  		for (String string : strings) {
  			if (filter.accept(string)) {
  				list.add(prefix + string);
  			}
  		}
  	}
docs: Add strings accepted by this filter pattern but prefixed with given string. Strings argument can come from
  {@link File#list()} and can be null in which case this method does nothing. This method accept a prefix argument; it is
  inserted at every string start before actually adding to strings list.
  
  <pre>
  File directory = new File(&quot;.&quot;);
  FilteredStrings files = new FilteredStrings(&quot;index.*&quot;);
  files.addAll(&quot;/var/www/&quot;, directory.list());
  </pre>
  
  If <code>directory</code> contains files like <em>index.htm</em>, <em>index.css</em>, etc. will be added to
  <code>files</code> but prefixed like <em>/var/www/index.htm</em>, respective <em>/var/www/index.css</em>.
  
  @param prefix prefix to insert on every string,
  @param strings strings to scan for pattern, possible null.