What happens when the type parameter is not defined when constructing a TreeSet in java?

Question

What is the expected result when the type parameter is not defined such as in the below code- Code Segment 1:

java.util.Set set = new java.util.TreeSet();
set.add(2);

Code Segment 2:

java.util.Set set = new java.util.TreeSet();
set.add("2");

Code segment 1 and 2 run fine. Code Segment 3:

java.util.Set set = new java.util.TreeSet();
set.add("2");
set.add(3);

Code Segment 4:

java.util.Set set = new java.util.TreeSet();
set.add(2);
set.add("3");

Code segment 3 and 4 fail with following errors respectively:

Exception in thread "main" java.lang.ClassCastException: class java.lang.String cannot be cast to class java.lang.Integer

Exception in thread "main" java.lang.ClassCastException: class java.lang.Integer cannot be cast to class java.lang.String

So does java take up the first addition as the default type for the set? Also, the error seems to be weird, shouldn't it be Integer to String for Code Segment 3 and String to Integer for Code Segment 4?

Additionally, what happens for other collections if type parameter is not defined?

To your last question, it's because the `TreeSet` is trying to compare the newly inserted value to the existing values in the set using `compareTo`. — chrylis -cautiouslyoptimistic-, Jun 12 '21 at 03:21
Alright got the point, thank you @chrylis-cautiouslyoptimistic- — Aadarsh, Jun 12 '21 at 06:41

What happens when the type parameter is not defined when constructing a TreeSet in java?

0 Answers0