What will be the output when you add custom elements in HashSet?

Problem statement: Given code is

1. import java.util.HashSet;
2. class A {}
3. class B {}
4. class C {}
5. public class Test {
6. public static void main(String[] args) {
7. HashSet set = new HashSet();
8. set.add(new A());
9. set.add(new B());
10. set.add(new C());
11. set.add(new A());
12. System.out.println("Elements: \n" + set);
13.   System.out.println("Size: " + set.size());
14. }
15. }

Answer:
Elements: 
[com.practice.core.C@7852e922, com.practice.core.A@15db9742, com.practice.core.B@6d06d69c, com.practice.core.A@4e25154f]
Size: 4