 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Java Forum / General / October 2006Deque question
Hi, Java ArrayDeque is an Deque implementation over an array. However if the array is gull it expands it, otherwise wraps the head and tail. That is what I want. However as it is an implementation over an array, I expect an random access like E get(index i) method. But such method is not present. Why? It is present in ArrayList or any other random access container! Though it gives an delete(index i) method, which causes it to shift some of the elements! can anyone give a little insight? Thanks abir > Java ArrayDeque is an Deque implementation over an array. However if > the array is gull it expands it, otherwise wraps the head and tail. [quoted text clipped - 4 lines] > it gives an delete(index i) method, which causes it to shift some of > the elements! I can only guess that it is to make it easier to subclass. Personally, I would have made it implement List (and RandomAccess, but not Cloneable). Tom Hawtin > Java ArrayDeque is an Deque implementation over an array. However if > the array is gull it expands it, otherwise wraps the head and tail. [quoted text clipped - 4 lines] > it gives an delete(index i) method, which causes it to shift some of > the elements! It seems to me that this is line with the design of the interface. Being a Queue at heart it seems logical to disallow index based operations and try to restrict access to only head and tail elements. > Being a Queue at heart it seems logical to disallow index based > operations and try to restrict access to only head and tail elements. Quite right. > > Being a Queue at heart it seems logical to disallow index based > > operations and try to restrict access to only head and tail elements. > Quite right. However it allows index based deletion! What is the problem with index based access? Otherwise what is the necessity to implement it over an Array? Surprisingly enough LinkedList , which is not backed by and array, and implements Deque has an index based access! A Deque property does not get lost giving index based access, it looses the property when it allows index based insert and remove (which it has already done!) Thanks >>> Being a Queue at heart it seems logical to disallow index based >>> operations and try to restrict access to only head and tail elements. [quoted text clipped - 8 lines] > > Thanks Isn't the index based delete method private? http://download.java.net/jdk6/doc/api/java/util/ArrayDeque.html does not mention it. Patricia > However as it is an implementation over an array, I expect an random > access like E get(index i) method. But such method is not present. Why? I Assume you're talking about the ArrayDeque in JDK1.6 ? If so then I can't see any good reason. It seems daft to me. Looking at the code, it seems that the only reason for that omission (and also the only reason for the equally odd restriction that the inserted values cannot be null) is to simplify the code a little and reduce the amount of arithmetic bounds checking needed. If so then (IMO) that/those are very poor reasons, and not at all what I would expect when: @author Josh Bloch and Doug Lea Note that the iterator /does/ make use (internally) of indexed access... Still, 1.6 is beta software, so maybe this'll change before release. -- chris > Looking at the code, it seems that the only reason for that omission (and also > the only reason for the equally odd restriction that the inserted values cannot [quoted text clipped - 3 lines] > > @author Josh Bloch and Doug Lea As a rule, collection classes written by Josh Bloch permit nulls, those written by Doug Lea do not. > Note that the iterator /does/ make use (internally) of indexed access... I would hope so. Note, the iterator does support remove... Tom Hawtin > > However as it is an implementation over an array, I expect an random > > access like E get(index i) method. But such method is not present. Why? > > I Assume you're talking about the ArrayDeque in JDK1.6 ? Yes, ArrayDeque in JDK1.6 beta . This class is a very important addition (esp for me!, and may be a very strong reason why I am using 1.6, apart from Those taskbar icons etc). > If so then I can't see any good reason. It seems daft to me. But it is beta version. I don't think API will change after a beta release. > Looking at the code, it seems that the only reason for that omission (and also > the only reason for the equally odd restriction that the inserted values cannot [quoted text clipped - 3 lines] > > @author Josh Bloch and Doug Lea Is he same person as Joshua Bloc of effective Java? Then I have a reason! He was in hurry while leaving Sun (and joining Google) :) I have an old code by them also, a non-generic version. > Note that the iterator /does/ make use (internally) of indexed access... Yes, everything uses indexed access, and that is natural when it is implemented over an array! And oh! The delete(int index ) is private, and have a special use in removeLastOccurrence and removeFirstOccurrence. It shifts the references using arraycopy. > Still, 1.6 is beta software, so maybe this'll change before release. Hope so! Thanks > -- chris Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
|
Reply to this Message
|
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.