Is a Collection better than a LinkedList?

Question

Collection list = new LinkedList(); // Good?
LinkedList list = new LinkedList(); // Bad?

First variant gives more flexibility, but is that all? Are there any other reasons to prefer it? What about performance?

Answer 1

These are design decisions, and one size usually doesn't fit all. Also the choice of what is used internally for the member variable can (and usually should be) different from what is exposed to the outside world.

At its heart, Java's collections framework does not provide a complete set of interfaces that describe the performance characteristics without exposing the implementation details. The one interface that describes performance, RandomAccess is a marker interface, and doesn't even extend Collection or re-expose the get(index) API. So I don't think there is a good answer.

As a rule of thumb, I keep the type as unspecific as possible until I recognize (and document) some characteristic that is important. For example, as soon as I want methods to know that insertion order is retained, I would change from Collection to List, and document why that restriction is important. Similarly, move from List to LinkedList if say efficient removal from front becomes important.

When it comes to exposing the collection in public APIs, I always try to start exposing just the few APIs that are expected to get used; for example add(...) and iterator().

Answer 2

Collection list = new LinkedList(); //bad

This is bad because, you don't want this reference to refer say an HashSet(as HashSet also implements Collection and so does many other class's in the collection framework).

LinkedList list = new LinkedList(); //bad?

This is bad because, good practice is to always code to the interface.

List list = new LinkedList();//good

This is good because point 2 days so.(Always Program To an Interface)

Answer 3

Use the most specific type information on non-public objects. They are implementation details, and we want our implementation details as specific and precise as possible.