Duplicate objects in ArrayList are references to a single one?

I have an ArrayList that has some objects that I defined in it. Based on some criteria, I want to copy some of the objects from the first list to the second list (which starts empty), but these objects that I copy could be copied several times ( can be duplicates ).

To simplify for an example let's say my second list contains only 2 objects that are duplicates. Objects a and b.

If I modify something in object a, will that modification also appear on object b ? It is just a reference that is passed or it's a copy of an object?

for( int i = 0; i < Selected.size(); i++)
            {
                double chance = random.nextInt(100);
                chance = chance/100;
                if( chance >= constCrossover ) 
                {
                    Cross.add(Selected.get(i)); 
                     //here i add items that might be duplicates
                }
            }

I will make further modifications in the Cross list and i don't want duplicate objects to interact with eachcother.