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Introduction of java.util.Queue in Java Tiger

somkiat puisungnoen
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Joined: Jul 04, 2003
Posts: 1312
In my opinion, java.util.Queue is good new api for java.

A collection designed for holding elements prior to processing. Besides basic Collection operations, queues provide additional insertion, extraction, and inspection operations.

Queues typically, but do not necessarily, order elements in a FIFO (first-in-first-out) manner. Among the exceptions are priority queues, which order elements according to a supplied comparator, or the elements' natural ordering, and LIFO queues (or stacks) which order the elements LIFO (last-in-first-out). Whatever the ordering used, the head of the queue is that element which would be removed by a call to remove() or poll(). In a FIFO queue, all new elements are inserted at the tail of the queue. Other kinds of queues may use different placement rules. Every Queue implementation must specify its ordering properties.

The offer method inserts an element if possible, otherwise returning false. This differs from the Collection.add method, which can fail to add an element only by throwing an unchecked exception. The offer method is designed for use when failure is a normal, rather than exceptional occurrence, for example, in fixed-capacity (or "bounded") queues.

The remove() and poll() methods remove and return the head of the queue. Exactly which element is removed from the queue is a function of the queue's ordering policy, which differs from implementation to implementation. The remove() and poll() methods differ only in their behavior when the queue is empty: the remove() method throws an exception, while the poll() method returns null.

The element() and peek() methods return, but do not remove, the head of the queue.

The Queue interface does not define the blocking queue methods, which are common in concurrent programming. These methods, which wait for elements to appear or for space to become available, are defined in the BlockingQueue interface, which extends this interface.

Queue implementations generally do not allow insertion of null elements, although some implementations, such as LinkedList, do not prohibit insertion of null. Even in the implementations that permit it, null should not be inserted into a Queue, as null is also used as a special return value by the poll method to indicate that the queue contains no elements.

Queue implementations generally do not define element-based versions of methods equals and hashCode but instead inherit the identity based versions from class Object, because element-based equality is not always well-defined for queues with the same elements but different ordering properties.



What do you think about Queue API in Java Tiger?


SCJA,SCJP,SCWCD,SCBCD,SCEA I
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Pradeep bhatt
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Joined: Feb 27, 2002
Posts: 8919

It is a good feature. Read the tutorial here
www.devx.com/Java/Article/21983/0/page/2


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Ko Ko Naing
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Joined: Jun 08, 2002
Posts: 3178
Yikes, then how can a lecturer in university let the student implement the Queue ADT in Data Strcutures course? I still remember the time when I was in the second semester of the first year in BSCS... I spent day and night to implement Queue using ANSI C and its famous pointer...

Cool!!! Now I can get Queue class easily by importing just java.util.Queue... but will it make the student to be lazy to implement such ADT, for they will always be looking for ready-made classes like this? :roll:


Co-author of SCMAD Exam Guide, Author of JMADPlus
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somkiat puisungnoen
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Joined: Jul 04, 2003
Posts: 1312
Thank you very much.
Pradeep bhatt
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Joined: Feb 27, 2002
Posts: 8919

Yikes, then how can a lecturer in university let the student implement the Queue ADT in Data Strcutures course?


Yes, I did it using C. The lecturer can ask the students to implement queue without using java.util.Queue.
Gregg Bolinger
GenRocket Founder
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Joined: Jul 11, 2001
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    6

Originally posted by Ko Ko Naing:
Yikes, then how can a lecturer in university let the student implement the Queue ADT in Data Strcutures course? I still remember the time when I was in the second semester of the first year in BSCS... I spent day and night to implement Queue using ANSI C and its famous pointer...

Cool!!! Now I can get Queue class easily by importing just java.util.Queue... but will it make the student to be lazy to implement such ADT, for they will always be looking for ready-made classes like this? :roll:


I think that is one of those catch 22 types of things. What I mean, for those that have never heard the expression, is that having those ready-made API's is great! But those that take them for granted and don't look into the how and why will always be a step behind those that do.

I still firmly believe that any CS type of degree program needs a C class with an emphasis on data structures and algorithms.


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