? with a Vector of LinkedLists

Question

Hi,
I would like to create a Vector. Each element will be a LinkedList. Each element in my LinkedList will be an Object, call it o. Obejcts like o have a member field called time, which is a BigDecimal. I am doing this because I want each LinkedList to contain o's with the same time value. So if I index into the Vector at 0 I will get a linked list that has Objects of type o and all those objects have time value t0. If I index into the Vector at position x, I will get a LinkedList of objects having time value tx.
Now, initially my Vector just contained the Objects of type o, so my class just had a method called compareTo() that would provide a natural ordering. This allowed me to do a Collections.binarySearch() when I wanted to insert into the vector.
Currently I am a little confused as to how and where I will write the new compareTo() method. Basically I have a method that accepts objects of type o and what I want it to do would be to look at o's time field, then do Collections.binarySearch() on the Vector to find the index of the appropriate LinkedList. Then I will just insert into the LinkedList. But I see that the LinkedList class does not have it's own compareTo() method. If I were to write one I would have it simply call the compareTo() method on the first element in it's list.
Thanks,
Jeff

Answer 1

Oh, ok. So you are basically implying that since my
times will be arbitrary then my binarySearch into the
Vector will cost more than just inserting a new
LinkedList into a HashMap (or getting the already
existing linked list from the HashMap). Makes sense.
Thanks.Not necessarily that it will be computationally more expensive, just that the vector is a poorer representation of your intent. A Vector (actually, ArrayList would be better) or Array is useful for random access when you know the index. If you want a lookup by an arbitrary key, however, a Map is a more direct realization of your design.
Under the covers, the Map could very well do a binary search on a List or array anyway, but your code shouldn't know or care about that detail. Your code should just say, as simply and directly as possible, "Give me the elemnts that have a time value of X". map.get(X) is a clean way to do that. Anybody reading the code later (including you, after you've forgotten WTF you were doing) will find that easier to understand than a binary search through a vector to find the list element whose first entry have time value X.