Why are empty collections of different type equal?

Question

What is mechanism below that makes equal different types?

import static org.testng.Assert.assertEquals;

@Test
public void whyThisIsEq         


        

Answer 1

They are not...

System.out.println(new HashSet<>().equals(new ArrayList<>())); // false

This is specific to testng assertEquals

Looking at the documentation of that method it says:

Asserts that two collections contain the same elements in the same order.

And this is ridiculous to me, a Set does not have an order, per-se.

Set set = new HashSet<>();
set.add("hello");
set.add("from");
set.add("jug");

System.out.println(set); // [from, hello, jug]

IntStream.range(0, 1000).mapToObj(x -> x + "").forEachOrdered(set::add);
IntStream.range(0, 1000).mapToObj(x -> x + "").forEachOrdered(set::remove);

System.out.println(set); // [jug, hello, from]

So comparing these against a Collection at some particular point in time would yield interesting results.

Even worse, java-9 Set::of methods implement a randomization internally, so the order (or not the order) will be different from run to run.