A Generic Class is Shared by all its Invocations
hello all,
i am not understanding what this means
all instances of a generic class have the same run-time class, regardless of their actual type
i am taking this to mean that no matter how many instances of list i create underneath it all 1 class is actually holding all my data for all instances. is this correct?
maybe i am not clear on the definition of a runtime class.
how does this affect my programming? will calling static methods on one instance affect the others?
i am confused
thanks
ed
i am not understanding what this means
all instances of a generic class have the same
run-time class, regardless of their actual typeInstances of the generic class ArrayList<E> could be for example ArrayList<Integer>, ArrayList<String>, or ArrayList<Date>. What the phrase above means is that, although the actual type of these instances is different (the types contained in the list are different), at run-time (when your program executes), they are still of the same class, namely ArrayList. This is because the compiler removes all references to the types at compile time (called type erasure). So, an ArrayList<Integer> is not another class than ArrayList<String>.
i am taking this to mean that no matter how many
instances of list i create underneath it all 1 class
is actually holding all my data for all instances. is
this correct?This is not correct. That instances of generic types have the same run-time class is not related to the data the instances contain. As mentioned by Malvolio, only static data is contained in the class (and hence shared among instances). Instance data is stored in the instance and hence can be different for every instance of a class. But this is true for all kinds of classes, not only generic ones.
how does this affect my programming? will calling
static methods on one instance affect the others?If the static method modifies static data of the class, this will affect other instances since static data is shared by all instances of a class. But again, this holds for all kinds of classes, not only generic ones.
i am confusedHope you�re not anymore.
Cheers
Matthijs
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Need help with generic class with comparable type
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First the good news. Your code has compiled. Those are warnings not errors. A warning is the compiler's way of saying "I understand what you are asking but maybe you didn't fully think through the consequences and I just thought I would let you know that...[something] "
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Hello all, here is my generic observer/ subject code.
package jstock;
* @author yccheok
public interface Observer<S, A> {
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cheokHowever, when I try to implements more than one classMore than one interface, you mean.
May I know how I can avoid the error message?You can't implement a generic interface more than once.
http://angelikalanger.com/GenericsFAQ/FAQSections/ProgrammingIdioms.html#Can%20a%20class%20implement%20different%20instantiations%20of%20the%20same%20parameterized%20interface? -
Hi All,
I am looking at porting over our current Java application from Java 1.4.2 to Java 1.5.
One of the main reasons is because of the CDS facility in Java 1.5.
Running the same app, one on 1.4.2 and the other on 1.5, on 1.5 it uses about 20% more memory !!!!
This application involves 3 JVM's running communicating via RMI.
When I start each of the applications with -Xshare:on, the first starts fine, indicating it is using CDS,
(-showversion parameter will indicate sharing), but then the next two wont start giving an error indicating
the shared archive cannot be accessed.
Before I started the apps I manually created the shared archive using the call java -Xshare:dump which
places the classes.jsa file in the directory jre/lib/i386/client/classes.jsa
I am running an Intel Solaris platform.
Any ideas why this isnt working ?ok, I have some more information after doing more investigation...
Here is the bug which I submitted to Sun...
FULL OS VERSION :
SunOS con1 5.8 Generic_108529-29 i86pc i386 i86pc
A DESCRIPTION OF THE PROBLEM :
I am running an application with 3 JVM's. I have manually enabled Class Data Sharing using the command java -Xshare:dump. This seems to work fine.
When I start the first JVM with the command line option -Xshare:on it seems to start fine and indicates "sharing" when I print out -showversion.
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THE PROBLEM WAS REPRODUCIBLE WITH -Xint FLAG: No
THE PROBLEM WAS REPRODUCIBLE WITH -server FLAG: No
STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Try to execute a JVM with class data sharing on, then try it again with class data sharing on, AND trying to set the maximum heap size.
EXPECTED VERSUS ACTUAL BEHAVIOR :
It should still allow CDS.
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An error has occured while processing the shared archive file. Unable to reserve shared region. Error occurred during initialization of VM Unable to use shared archive.
REPRODUCIBILITY :
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