Generic Collections and inheritance
Hi all
I have the following code:
public class GenericTest {
public static <T,C extends Collection<T>> C process(C collection){
// do some stuff (using T)
return collection; // just to make a complete methode
public void main(String[] args){
List<String> l1 = new ArrayList<String>();
List<String> l2;
l2 = process(l1); // does not compile
}Compilation fails with message :
Bound mismatch: The generic method process(C) of type GenericTest is not applicable for the arguments (List<String>) since the type List<String> is not a valid substitute for the bounded parameter <C extends Collection<T>>
My questions:
why doesn't it work?
How do I fix it?
regards
Spieler
What Compiler are you using?
Your code compiles just fine on the JDK 1.5 compiler (once I added an inport for java.util.*)
If the error message is from your IDE, you should check your IDE's web site for an existing bug, and for assistance.
This is not the correct forum since your code compiles on the SUN JDK.
Bruce
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Generic classes and inheritance
I am in the midst of converting some database object code over to split the data from the database functionality, and I am coming into issues with generics.
I have three bean classes:
abstract public class Payment {
// common fields and their get/set methods
public final class AU_Payment
extends Payment {
// extra fields and their get/set methods
public final class US_Payment
extends Payment {
// extra fields and their get/set methods
}The code to write these classes to the database used to be in those classes, now I am moving them out to their own classes. I need to have a similar hierarchy so I can obtain an instance of the right class (through a factory) to write these objects to the database.
public interface PaymentDB<T extends Payment> {
public Result load(Connection conn, T payment, ResultInfo resultInfo) throws SQLException;
public Result loadAll(Connection conn, List<T> allPayments, ResultInfo resultInfo) throws SQLException;
}If I have the code for the AU_PaymentDB as the following, it won't compile:
public class AU_PaymentDB<AU_Payment> {
public Result load(Connection conn, AU_Payment payment, ResultInfo resultInfo) throws SQLException {
return null;
public Result loadAll(Connection conn, List<AU_Payment> payment, ResultInfo resultInfo) throws SQLException {
return null;
}the compiler complains that the class doesn't override the interface, and I need to recode it to the following to get it to compile:
public class AU_PaymentDB<AU_Payment> {
public Result load(Connection conn, Payment payment, ResultInfo resultInfo) throws SQLException {
return null;
public Result loadAll(Connection conn, List payment, ResultInfo resultInfo) throws SQLException {
return null;
load now takes just a Payment in it's signature list, and loadAll takes an untyped List.
This means I can actually call load() with a US_Payment and it works fine, which I don't want. Also, I cannot add an AU_Payment to the list in loadAll, because the list is of the wrong type.
How do I fix this? I want the AU_PaymentDB class to only act upon AU_Payments, and I need the loadAll to be able to add new AU_Payments to the list that is passed in.
I hope this all makes sense,
Chrisok, I'm assuming that you just forgot to paste in that AU_PaymentDB implements PaymentDB :-)
parameterize AU_PaymentDB as follows:
public class AU_PaymentDB implements PaymentDB<AU_Payment> {
public Result load(Connection conn, AU_Payment payment, ResultInfo resultInfo) throws SQLException {
return null;
public Result loadAll(Connection conn, List<AU_Payment> payment, ResultInfo resultInfo) throws SQLException {
return null;
}so the interface defines a looser parameter ( Payment ) and your implementation drills it down to more specifically AU_Payment
Bob, I believe, is your uncle -
Generic methods and inheritance
Hello,
I have a class structure like this:
A - - - - > IA (A implements IA)
C - - - - > IC -------> IB (C implements IC extends IB)
In IA I have a method create that returns <T extends IB<T>>:
public interface IA {
public <T extends IB<T>> T create();
}IB:
public interface IB<T> {
}IC extends IB like this:
public interface IC extends IB<IC> {
}C implements IC:
public class C implements IC{
}Finally the problem: I wan to implement A in order to return an IC in the create method:
public class A implements IA{
public IC create() {
IC c = new C();
return c;
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What is the proper way to create such a structure?
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Basically I have a class
public class GModel <C>{
protected C data;
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}//On my guess, when I do
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So, usign the netbeans when I do
MyObject obj = abcModel.getData();I should not use any casting, since the generics would tell that return object from getDta would be the MyObject.
Is this right? If yes; did someone try to do that on netbeans?
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public abstract class PersistableObject
implements Serializable {
private static final long serialVersionUID = 1L;
private String id = UUID.randomUUID().toString();
private Long version;
public PersistableObject() {
this(serialVersionUID);
public PersistableObject(final Long paramVersion) {
version = paramVersion;
public String getId() {
return id;
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id = paramId;
public Long getVersion() {
return version;
public void setVersion(final Long paramVersion) {
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public String toString() {
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private static final long serialVersionUID = 1L;
private String name;
private T value;
public PropertyBase() {
this(serialVersionUID);
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this(paramVersion, null);
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this(paramVersion, paramName, null);
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super(paramVersion);
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public String getName() {
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public void setName(final String paramName) {
name = paramName;
public T getValue() {
return value;
public void setValue(final T paramValue) {
value = paramValue;
public class ShortProperty extends PropertyBase<Short> {
private static final long serialVersionUID = 1L;
public ShortProperty() {
this(null, null);
public ShortProperty(final String paramName) {
this(paramName, null);
public ShortProperty(final String paramName, final Short paramValue) {
super(serialVersionUID, paramName, paramValue);
public class StringProperty extends PropertyBase<String> {
private static final long serialVersionUID = 1L;
protected StringProperty() {
this(null, null);
public StringProperty(final String paramName) {
this(paramName, null);
public StringProperty(final String paramName, final String paramValue) {
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private static final long serialVersionUID = 1L;
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private ShortProperty number = new ShortProperty("number");
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this(serialVersionUID);
public ElementModel(final Long paramVersion) {
super(paramVersion);
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return name.getValue();
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<?xml version="1.0" encoding="UTF-8" ?>
<entity-mappings version="2.1"
xmlns="http://xmlns.jcp.org/xml/ns/persistence/orm" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence/orm http://xmlns.jcp.org/xml/ns/persistence/orm_2_1.xsd">
<mapped-superclass
class="PersistableObject">
<attributes>
<id name="id">
<column name="id" />
</id>
<version name="version" access="PROPERTY">
<column name="version" />
</version>
</attributes>
</mapped-superclass>
<entity class="PropertyBase">
<table name="PropertyBase" />
<inheritance />
<discriminator-column name="type"/>
<attributes>
<basic name="name">
<column name="name" />
</basic>
<basic name="value">
<column name="value" />
</basic>
</attributes>
</entity>
<entity class="StringProperty">
<discriminator-value>StringProperty</discriminator-value>
</entity>
<entity class="ShortProperty">
<discriminator-value>ShortProperty</discriminator-value>
</entity>
<entity class="ElementModel">
<table name="ElementModel" />
<inheritance />
<discriminator-column name="type"/>
<attributes>
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<join-column name="name" referenced-column-name="id" />
<cascade>
<cascade-all />
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<join-column name="number" referenced-column-name="id" />
<cascade>
<cascade-all />
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</attributes>
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</entity-mappings>
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public ElementModelTest() {
super(ElementModel.class);
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@SuppressWarnings("unchecked")
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em.getTransaction().begin();
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ElementModel device = new ElementModel();
device.setName("ElementModel: " + i);
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em.persist(device);
em.getTransaction().commit();
modelList = q.getResultList();
System.out.println("size after insert: " + modelList.size());
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em.close();This was answered in a cross post here java - EclipseLink + JPA + Generic Entity + SINGLE_TABLE Inheritance - Stack Overflow
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First of all searching for collections and tags can *not* be done simultaneously. You can either work with one collection only, or you can search for pictures with one or more tags.
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How to extract data from generic view and function module
hi experts,
can anybody give me the steps to extract data from generic view and functon modules.
thanks and regards
venkathttps://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/a0f46157-e1c4-2910-27aa-e3f4a9c8df33
https://websmp103.sap-ag.de/~sapidb/011000358700007535452002
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Apex Collections and Dates
I made an earlier posting today on the forum titled “‘ORA-01861: literal does not match format string’ error after my hosting company upgraded to Apex 3.2.” The issue relates to Apex collections and dates. Prior to the hosting company upgrading Apex 3.2 from 3.1 all was working OK. It seemed a reasonable assumption that the issue relates to the upgrade to 3.2. Having tested the code against another Apex 3.2 installation I am satisfied that the issue is not with Apex 3.2. That said, I am still getting the issue on the hosting site.
To demonstrate the issue to my hosting company and this forum, I put together a simple one page application that demonstrates the issue using the least amount of code.
I created a page with an ‘On Load – Before header” process that sets up an Apex Collection with a single value of ’20-FEB-2009’ in the c001 element as follows:
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end if;
apex_collection.create_collection(p_collection_name => 'THEISSUE');
APEX_COLLECTION.ADD_MEMBER(
p_collection_name => 'THEISSUE',
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I added an SQL REPORT region to the page which uses the Apex Collection as follows:
select to_date(c001,'DD-MON-YYYY') testdate
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and to_date('20-FEB-2009','DD-MON-YYYY')
= to_date(c001,'DD-MON-YYYY')
and run the page, the date is displayed OK, i.e., c001 is converted to a date OK. This made me wonder whether it does not like the line to_date('20-FEB-2009','DD-MON-YYYY')? So I changed the where code for the report to :
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It would seem on my hosting site since the upgrade, that Apex and Oracle have problems with Apex Collection elements being converted to dates as part of the where clause.
Now my understating of Oracle Apex collections in simple terms is that all Apex collections are held in a single Oracle table managed by a series of Apex functions. Given that all Apex collections are in the same table, could the issue be with the Oracle database when it is creating its execution plan for the query? Could Oracle be including the value of c001 from other collections (i.e., when c001 is not in a date format ) in the initial stages of its execution plan?
I hope the above make sense and thanks in advance.
IanScott,
I believe I have found the answer the statistics on WWV_FLOW_COLLECTIONS$ and WWV_FLOW_COLLECTION_MEMBERS$. are out of date and Oracle is doing a full table scan instead of using the indices to select only the c001 columns that belong to the given collection_id. If I change my simple example to store the date value in c050 it works ok. (In all probability this will be the only collection on the hosted database to use c050).
I have asked the hosting company to gather stats on all the apex tables.
Thanks for your help
Ian -
I finally upgraded from Firefox 3.6.8 to Firefox 7.0 this morning. I don't like the default theme, so I tried to download a new persona and do not see a "wear this" button any longer. On the screen where I should see a button that installs it on my desktop, I have an option to download Firefox or to add the persona to a collection. I created a collection and added 2 themes, but even that won't allow me to actually install the persona in Firefox.
Try a reset ...
Press and hold the Sleep/Wake button and the Home button together for at least ten seconds, until the Apple logo appears.
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Creation of a generic extractor and data source for the FAGLFLEXA table
Hi All,
Need to create a generic extractor and data source for the FAGLFLEXA table to support AR reporting. This table contains the necessary profit center information to perform LOB reporting against the AR data.
Please advice on how to do this.
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Its seems a simple a work out.
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Dear Apple,
I am unable to download itones app for my windows pc that site says like "Now that you’ve downloaded iTunes, you’re just a few steps away from starting a digital entertainment collection and enjoying it on your Mac, PC, iPad, iPhone or iPod." but i couldn,t find in system.
please send the itones downloads link.
Thanks
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Thank you for your reply.
Devices should appear in the top right of iTunes, as seen in this image:
From:
iTunes 11 for Windows: Connect a device
http://support.apple.com/kb/PH12449
If you do not see your iOS device in this menu when you connect it to your computer, it may not be recognized by iTunes. In this case, I recommend the troubleshooting steps in this article:
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http://support.apple.com/kb/TS1538
Best,
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