CODEWITHSUNDEEP
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user183037
user183037

Reputation: 2579

What's the difference between the element() and getFirst() methods in the LinkedList class?

LinkedList has similar descriptions for the element() method and the getFirst() method (strangely - not the same words).

Deque clearly states that the two methods are the same in terms of the return value and the exception.

My question is - why have 2 identical methods? Is it for backward compatibility? Is one approach more efficient than the other?

Upvotes: 11

Views: 7204

Answers (3)

Sean Patrick Floyd
Sean Patrick Floyd

Reputation: 299218

In Java 1.6, LinkedList implements Deque (Double-ended Queue). From the Deque.element() javadocs:

Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from peek only in that it throws an exception if this deque is empty.

This method is equivalent to getFirst().

In Java 1.5, LinkedList has both methods, but getFirst() is not backed by an interface. My guess is that in Java 1.6 they implemented Deque intentionally to include this method.

In Java 1.4, LinkedList only has the getFirst(), but it isn't backed by an interface.

Obviously I'd say this is an issue of maintaining backwards compatibility:

  • LinkedList 1.4 has getFirst() and only the List interface
  • LinkedList 1.5 implements Queue and hence needs to support the equivalent elements() method
  • LinkedList 1.6 implements Deque but because a) it has to remain backwards compatible and b) by policy, all methods should be backed by interfaces, the Deque interface also includes the duplicate method

Upvotes: 3

Joey
Joey

Reputation: 354874

element() is inherited from Queue where it makes sense to have only one accessing method since all you can do in a queue is remove the first element. However, a deque supports this from both ends, necessitating explicit methods to do so.

And it's not very nice to design an API where you would access the first element with element() and the last with getLast().

Another thing that might play into this is that Deque was added in 1.6, where parts of the ancient parts of the Java Collections Framework have been obsoleted by newer conventions, such as explicit get~/set~ methods for property access. In that context, getFirst() and getLast more closely adhere to the current Java conventions.

Upvotes: 8

Falmarri
Falmarri

Reputation: 48615

In a link listed it looks like those are the same. But in a Queue, element() seems to be a method to peak at the first element in the queue, but not remove it from the queue.

Upvotes: 0

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