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plurals

POGetting a single instance of an object
primarykey
Id
3415942
data
AcceptedAnswerId
3416219
AnswerCount
4
ClosedDate
CommentCount
6
CommunityOwnedDate
CreationDate
2010-08-05T14:50:37.163
FavoriteCount
0
LastActivityDate
2010-08-05T15:22:30.420
LastEditDate
2010-08-05T15:05:19.060
LastEditorUserId
412034
OwnerUserId
412034
ParentId
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PostTypeId
1
Score
2
ViewCount
4376
LastEditorDisplayName
text
Body
Let's say I have a class <code>A</code> and this class has a List <code>l</code>. There is also a class <code>B</code> that extends <code>A</code> that will access the list <code>l</code>, as shown below. In my program, there must only be an instance of the class <code>B</code> (I'm using Singleton pattern), and there must be only one instance of the List <code>l</code> also, so I'm doing it like this: <pre><code>public abstract class A { protected List<String> l; public A() {} protected synchronized List<String> getList() { if (l == null) l = new LinkedList<String>(); return l; } } //--- public class B extends A { private static B instance; private B() { super(); } public static synchronized B getInstance() { if (instance == null) instance = new B(); return instance; } } </code></pre> What I want to do is: In one instance of <code>B</code>: <pre><code>System.out.println(super.getList().size()); //must print 0 super.getList().add("a"); System.out.println(super.getList().size()); //will print 1 </code></pre> In another instance of <code>B</code>: <pre><code>System.out.println(super.getList().size()); //should print 1, cause i've already //added "a", but prints 0 super.getList().add("b"); System.out.println(super.getList().size()); //should print 2, but prints 1 </code></pre> That is not working as expected though. What am I doing wrong? Can anyone help me? <hr> EDITED: Hi, Bill the Lizard, here are the two classes: <pre><code>public abstract class A { protected static List<String> l; public A() {} protected static synchronized List<String> getList() { if (l == null) l = new LinkedList<String>(); return l; } } //--- public class B extends A { private static B instance; private B() { super(); } public static synchronized B getInstance() { if (instance == null) instance = new B(); return instance; } public void metodo() { System.out.println(super.getList().size()); super.getList().add("a"); System.out.println(super.getList().size()); } } </code></pre> And this is how i create an instance of B: <pre><code>public class ClassTeste { public static void main(String[] args) { B b = B.getInstance(); b.metodo(); } } </code></pre>
Tags
<java>
Title
Getting a single instance of an object
singulars
PostAcceptedAnswerId
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
PostParentId
1. This table or related slice is empty.
PostTypePostTypeId
1. PTQuestion
UserLastEditorUserId
1. USAntonioJunior
UserOwnerUserId
1. USAntonioJunior
plurals
PostLinksPostIdRelatedPostId
1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
2. PO
 singulars
 PostTypePostTypeId
 PTAnswer
3. PO
 singulars
 PostTypePostTypeId
 PTAnswer
VotesPostIdCreationDate
1. VO
 singulars
 PostPostId
 POGetting a single instance of an object
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
CommentsPostId

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