List<String> list = new ArrayList<String>;

public void myMethod(){
        List<String> removals = new ArrayList<String>(list.size());
    for (String s : list) {
        removals.add(stringMethod(s));
    }
        list.removeAll(removals);
}

public void stringMethod(s) {
    if (condition) {
        for (String s1 : list) { //concurrentmodificationexception on this line
            if (s1 == s) {
                continue;
            }
            //do stuff
        }
    }
        return s;
}