如何从两个不同的列表中删除重复项？

Question

I have two lists in java where I need to remove duplicates. One list contains a class (UrlInfo) with three fields, the other contains a list of strings. I need to compare the list of strings with a field from the class and remove duplicates from the list containing the class.

Here is what I have right now.

String urlString;
for (UrlInfo url : urlClass) {
  urlString = url.getUrl();
  for (int i = 0; i < storedUrlList.size(); i++) {
    if (urlString.equals(storedUrlList.get(i))) {
      urlClass.remove(url);
    }
  }
}

This is extremely slow for me. The lists that I will be working with will contain upwards of 100,000 elements.

Answer 1

I'd first iterate the List checking if they match the List, if so, I'd store them in a List and then call removeAll() like this:

List<String> toBeComparedWith ...
List<UrlInfo> toBeRemoved = new ArrayList<>();
for (UrlInfo uInfo : urlClass){
    if (toBeComparedWith.contains(uInfo.getUrl()){
        toBeRemoved.add(uInfo);
    }
}

urlClass.removeAll(toBeRemoved);

Answer 2

Because the list to be compared storedUrlList is a list of strings, so you can use the method List#contains(Object) to achieve the comparison, and remove the elements from your original list urlClasses .

In Java 7:

ListIterator<UrlClass> iterator = urlClasses.listIterator();
while (iterator.hasNext()) {
  UrlClass u = iterator.next();
  if (storedUrlList.contains(u.getUrl())) {
    iterator.remove();
  }
}

In Java 8:

urlClasses.removeIf(u -> storedUrlList.contains(u.getUrl()));