ArrayList.contains() return false on equals strings sometimes

Question

I have some trouble with my 'cache' list:

private static List<String> urlsCacheList = new ArrayList<String>();
...
 private static void parseUrlsToQueue(Content content){
        String str = content.toString();
        Pattern p = Pattern.compile(CSS_JS_PATTERN);
        Matcher m = p.matcher(str);
        while (m.find()) {
            String link = m.group();
            if(link.equals("http://static.gazeta.ru/nm2012/css/new_common_css_pda54.css")){
                LOG.warn("******************cache CONTAINS STRING http://static.gazeta.ru/nm2012/css/new_common_css_pda54.css " + urlsCacheList.contains(link) + " ;" + link +";" );
            }

            if(!urlsCacheList.contains(link)){
                urlsCacheList.add(link);
                queue.add(link);
            }
        }
    }

So after some iterations urlsCacheList.contains(link) return false on the equals links, and

LOG.warn("******************cache CONTAINS STRING http://static.gazeta.ru/nm2012/css/new_common_css_pda54.css " + urlsCacheList.contains(link) + " ;" + link +";" );

prints: cache CONTAINS STRING http://static.gazeta.ru/nm2012/css/new_common_css_pda54.css false ;http://static.gazeta.ru/nm2012/css/new_common_css_pda54.css;

But its mostly return true on the same strings, each 30 or 40 iterations its returns false;

UPDATE1: Sorry guys by its seems to me that problem in another place, I call parseUrls() method from Fetcher.class like that:

..
ContentParser.parseUrlsToQueue(content);
..

so after some iterations my urlsCacheList just re-init to null , becaus of own class re-creation;

Answer 1

Can you print the string object hash id's for the strings which fails the contains check. I think it might be because a new String object is created for few Strings and due to this its behaving like this.

One solution is to call String.intern() method to solve this problem.