Java – adding to HashMap takes a long time

In my java program, I have stopped for a few lines, which takes too much time (about 20 seconds), which seems strange to me

This is a thread

Map<URL,Integer> res2 = new HashMap<>();
 for (URL url : res) {
     res2.put(url,null);
 }

Which res is defined as follows:

List<URL> res = new ArrayList<>();

In my program, res.size() ~ = 1500

Do you know where my problem may come from?

thank you!

Solution

java. net. The hashcode () method of the URL performs DNS resolution The URL class is not suitable for use in HashSet or as a key in HashMap Use string or Java net. URI.

Here are some background knowledge:

> Michael Scharf: java. net. URL. equals and hashCode make (blocking) Internet connections…. > Eishay Smith: Java's URL little secret (link in robau's comments on this answer)