How to make a new list with a property of an object which is in another list

Question

Imagine that I have a list of certain objects:

List

And I need to generate another list including the ids of

Answer 1

It is Mathematically impossible to do this without a loop. In order to create a mapping, F, of a discrete set of values to another discrete set of values, F must operate on each element in the originating set. (A loop is required to do this, basically.)

That being said:

Why do you need a new list? You could be approaching whatever problem you are solving in the wrong way.

If you have a list of Student, then you are only a step or two away, when iterating through this list, from iterating over the I.D. numbers of the students.

for(Student s : list)
{
    int current_id = s.getID();
    // Do something with current_id
}

If you have a different sort of problem, then comment/update the question and we'll try to help you.