Miga: Thank You for your response, it is very clear and is the best explanation I have seen yet.
DaveB ________________________________ From: miga <[email protected]> To: Free Java Programming Online Training Course By Sang Shin <[email protected]> Sent: Monday, October 5, 2009 2:37:34 PM Subject: [java programming] Re: Collections Lab 1016 and Xlint: On Oct 4, 4:57 pm, DaveB <[email protected]> wrote: > 2. When I run the program, all is well. > However, when I Clean and Build to get the dist folder and jars, I get > warning to recompile with the -Xlint:unchecked compiler option. After > including this option in the compiler options for the project, the > output prints warnings for each Linked List add like: > > C:\Documents and Settings\Dave\My Documents\MyJava\MyOwnLinkedList\src > \myownlinkedlist\Main.java:33: warning: [unchecked] unchecked call to > add(E) as a member of the raw type java.util.LinkedList > > I have looked this up, but I am unclear as to what is an unchecked > call to add(E) means. > > Can someone help to explain? Normally, a collection is a set of specific "objects", objects being specified in the formation of the collection. That is the collection is a set of elements of given type, the type being specified when defining the collection. So, if you define the LinkedList as it is done, your LinkedList does not specified the type of the elements (aka the "objects") of the collection. So, it gives you the warning, E being the element of the collection. It means that it is not safe (i.e. Java cannot verify) that the element you add to the collection is of the given type, since you have not specified a type. Now you may define the collection this way: LinkedList<Object> myLinkedList = new LinkedList<Object>(); Notice that you say here that the elements of the collection are of type Object. Then you may add safely: myLinkedList.add(new whatever(args*)); Of course, the example is a little constraint, since you use Object as type, but you may for example use only String, or only Integer, what you really want in your collection. > > Thx, > DaveB --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/javaprogrammingwithpassion?hl=en -~----------~----~----~----~------~----~------~--~---
