Generic method signatures

I've searched but can't find that a question I have has been asked (or answered). I apologize in advance if it has. Here is my question.
In Java Generics FAQ by Angelika Langer states in FAQ 802 ( [http://www.angelikalanger.com/GenericsFAQ/FAQSections/TechnicalDetails.html#FAQ802] ) "the type parameters of a generic method including the type parameter bounds are part of the method signature."
In FAQ 810, many examples are presented of method declarations, including generic ones, and their corresponding method signatures. For example,
<T> T method(T arg) has the following signature in the example:
<$T1_extends_Object>method($T1_extends_Object>)
It would seem to be intuitively clear that the type parameter and bounds would be part of the method signature but I can't seem to find such a stipulation/requirement of such in the Java Language Specification. Anybody know where it's stipulated in the JLS?
Best Regards

user13143654 wrote:
Yeah, I know. The title of the subsection is "Determining Method Signature," but then it never seems to expressly do that other than in some ephemeral wafting byproduct of overload resolution.I wouldn't call it "ephemeral" and "wafting." It's pretty specific. If you're looking for the $T1_extends_Object notation, you won't find it. That's not part of the spec.
I can't seem to find a specific spot in the subsection where I can say "OK, now I've got the method signature and now can proceed to ..." Well, it goes on to Phase 3, and then on to 15.12.2.5 Choosing the Most Specific Method. I'm not sure what you're looking for. It does describe in detail how we get from all the methods in the universe, to which type's methods we'll be considering to which signatures could match to which one is the best match. I don't know what else you're looking for.
If you're looking for somebody to digest, translate, and simplify all that for you, good luck, but it ain't gonna be me. :-)
If you have specific questions about smaller pieces of it I (or somebody else) might be able to help out. At the moment though, your question is rather vague.
Edited by: jverd on May 3, 2011 1:48 PM

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Generic method signature help

Hello All,
I'm confused about the following generic method signature . Compilation fails
public class Animal{}
public class Dog extends Animal{}
public <E super Dog> List<E> methodABC(List<E> list){
The compiler gives the following error
E cannot be resolved to a type
E cannot be resolved to a type
Syntax error on token "super", , expected
if i change the declaration of E to <E extends Dog>, no compiler error.
An early response will be highly appreciated. Thanks in advance.
Kind Regards.
Hasnain Javed Khan.

you cannot use "super" on a type variable, only on wildcards

Generic Method override compatibility

I tried to find references to the problem but couldn't. I face it all the time and I thought some else must have had the same problem already.
Oh well, here it goes.
With both 3.1M4 and 3.1M5a the following code compiles without any problems.
public interface MyIface {
    public <T> void foo(T p);
public class MyClass implements MyIface{
    public <T extends Integer> void foo(T p) {
         //does something
}However, javac 1.5 gives me:
MyClass.java:1: MyClass is not abstract and does not override abstract method <T>foo(T) in MyIface
public class MyClass implements MyIface{
^
1 error
I found many different variations to this problem, which I am not going to list here as I am trying to be concise. But for the eclipse compiler, <T extends Integer> is the same as <T> in terms of method signature. For the javac compiler these are different thingss.
Does anyone know if this is a Bug in eclipse or javac, or if this is a known decision, which is taking both tools in different directions?
Coconha

Coco, you have to understand how generics work in the compiler to understand this. Basically, erasure means that all the fancy generics stuff you write in your source code gets 'erased' when it gets compiled... So:public interface MyIface {
    public <T> void foo(T p);
}gets compiled and the resulting .class file, if you decompiled it, would actually look like this:public interface MyIface {
    public void foo(Object p); // NOTICE that "T" gets erased to plain old java.lang.Object
}See? The same thing happens with MyClass:public class MyClass implements MyIface {
    public <T extends Integer> void foo(T p) {
         //does something
}after it's compiled, actually looks like this inside the .class file:public class MyClass implements MyIface {
    public void foo(Integer p) { // NOTICE that "T extends Integer" gets erased to plain old Integer!
         //does something
}Do you see what the problem is now? MyClass has a method called foo(Integer) and MyIface has a method called foo(Object). Obviously now, you see, foo(Integer) shouldn't override foo(Object). The Eclipse compiler should actually complain that you haven't implemented foo(Object) in MyClass. Do you follow?
Let's look at your second example.public class Base {
public <S> void foo(S a) {
    System.out.println("Base: " + a);
public class Sub extends Base {
public <S extends Integer> void foo(S a) {
    super.foo(a); // should be an error here! super.foo(Integer) doesn't exist!
    System.out.println("Sub: " + a);
}Let's apply erasure manually and see why there is no error:public class Base {
public void foo(Object a) {
    System.out.println("Base: " + a);
public class Sub extends Base {
public void foo(Integer a) {
    super.foo(a); // calls foo(Object a)! you could also write "this.foo((Object)a)"
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Are bridge methods generated for generic methods?

I've recently come across the notion of bridge methods. They provide type safety while allowing for erasure. However, the only places where they've been mentioned is with your class extending a parameterized type. That is the only case mentioned with bridge methods in the JLS as well as:
http://www.angelikalanger.com/GenericsFAQ/FAQSections/TechnicalDetails.html#Under which circumstances is a bridge method generated?
So I've been wondering about generic methods. For example, Collections.max's signature looks like the following in the source:
public static <T extends Object & Comparable<? super T>> T max(Collection<T> coll)
and after erasure:
public static Object max(Collection coll)
However, one cannot simply pass any type of Collection to the max method, it must implement Comparable and whatnot. Therefore, my question is how does it do that? Mustn't there be some sort of bridge method or generic information in the class file? Else how can the compiler, by just looking at the erasure of generic methods, check type safety, do capture conversion, type inference, etc?

Generic information is erased from the byte code. It is still there in the class file in the method signatures. That's how the compiler knows.

Reflection cant get parameterized method signature?

my sample:
interface Root<T>{
public void prt(T t );
interface A extends Root<String>{
public class Reflecttest {
public static void main(String[] args){
Class cl=A.class;
for (Method m:cl.getMethods()){
m.getParameterTypes();
//som reflection like above, but i cant get signature like public void prt(String str); but public void prt(Object o);
//how can i get the parameterized method signature
}

That information doesn't exist at runtime. It is all
erased to Object by the compiler. That's what
Generics does - safe type erasurefurther, you don't need to know, since by using reflection you're basically bypassing compile-time type safety altogether. reflection and generics have totally different intents, and don't mix well together

How to create a generic method?

Hi,
I am using a std task TS01200205 to create instance for a BOR object. There are 2 key fields. I want to pass these 2 to the ObjectKey field.
As for as I know, we have to concatenate these two Keyfields and assign it to 'Object Key' parameter.
How can I concatenate the 2 strings in my Workflow? Is there any std way of doing it?
Also what is a generic method? How to create it? Can I make use of generic method to achieve this?
Thanks,
Sivagami

If you want to use it in different workflows the best solution is probably to define an interface and define and implement the method there (a nice thing about BOR interfaces is that you can provide an implementation and not just the definition).
All you then need to do is let your object type(s) implement that interface, which only requires adding the interface since the implementation has been done already.
However, I am not saying this is a good way of approaching things, I'm just telling you how you can implement what you suggest.

How to create a generic method which invokes Web Service

Hi I have a question how to create Web Service client. In design mode I can't specify static url ?WSDL and process.
I found briliant method in apache cxf library.
for example
JaxWsDynamicClientFactory dcf = JaxWsDynamicClientFactory.newInstance();
Client clientA = dcf.createClient("http://soabpm-vm:8001/soa-infra/services/default/MailSender/mailsender_client_ep?WSDL");
Object[] resultA;
try{
resultA = clientA.invoke(new QName("http://xmlns.oracle.com/SynchDSBpel20/MailSender/MailSender", "process"), "@", "body", "topic");
}catch (Exception e){}
In my case I should create a method with params (urls ?WSDL, URI, operetion name, param1, praram2, param3)
Is there anything like CXF in ADF library's?

This can be very easily done using a web service proxy (Select web services from the categories and web service proxy from the items).
In the "Create Web Service Proxy" wizard, make sure you select JAX-WS client style. JDeveloper will use the JAX-WS web service API and JAXB (Java Architecture for XML Binding) to generate all required classes and methods required to call a web services, binding Java method signatures to WSDL messages and operations.
Regards
Antonis

[ABAP OO] Generic method get lines

Hi Experts,
I am creating a generic method to get the numbers of lines from any table, like below:
TABNAME type string.
LINES type i.
METHOD get_lines_from_any_dbtab.
DATA lo_tab TYPE REF TO data .
CREATE DATA lo_tab TYPE TABLE OF (tabname) .
SELECT * FROM (tabname) INTO TABLE lo_tab .
DESCRIBE TABLE lo_tab LINES lines .
CONDENSE lines
METHOD.
I have an error message during the compilation as:
LO_TAB is not an internal table.
Any idea ?
Kind regards.
Rachid.

Got it:
DATA lo_tab TYPE REF TO data .
FIELD-SYMBOLS <fs_dbtab> TYPE ANY TABLE .
CREATE DATA lo_tab TYPE TABLE OF (tabname).
ASSIGN lo_tab->* TO <fs_dbtab> .
SELECT * FROM (tabname) INTO TABLE <fs_dbtab> .
DESCRIBE TABLE <fs_dbtab> LINES lines .
CONDENSE lines .

No Method Signature - initQuery error after VO Substitution

Hi All,
I have done a VO Substitution for "NewBankAccountVOImpl". Below is the exact Requirement,
iReceivables -> Query for a given Customer -> Go to accounts Tab -> Try to Pay off an invoice -> You get an option choose Payment Method as "New Bank Account" ->
Now there are three field Routing Number, Account Number and Account Holder
I need to restrict Account Number to minimum three characters. In 11.5.10 Oracle do not have this validation.
So I checked out the place where the Routing Number and Account Number Validation happen i.e "NewBankAccountVOImpl" and extended the same to custom VOImpl and copied all the standard code to my custom code as below,
package mercury.oracle.apps.ar.irec.accountDetails.pay.server;
import oracle.apps.ar.irec.accountDetails.pay.server.NewBankAccountVOImpl;
import oracle.apps.ar.irec.accountDetails.pay.server.NewBankAccountVORowImpl;
import java.sql.Types;
import java.lang.String;
import oracle.apps.ar.irec.accountDetails.pay.utilities.PaymentUtilities;
import oracle.apps.ar.irec.framework.IROAViewObjectImpl;
import oracle.apps.fnd.common.VersionInfo;
import oracle.apps.fnd.framework.OAException;
import oracle.apps.fnd.framework.server.*;
import oracle.apps.fnd.framework.webui.OAWebBeanConstants;
import oracle.jbo.RowIterator;
import oracle.jbo.RowSetIterator;
import oracle.jbo.domain.Number;
import oracle.jbo.server.DBTransaction;
import oracle.jdbc.driver.OracleCallableStatement;
import oracle.jdbc.driver.OraclePreparedStatement;
// --- File generated by Oracle Business Components for Java.
// --------------- Modification History --------------------------
// Date Created By Description
// 04/01/2011 Veerendra K Account Number Validation to raise
// error if Account Number entered is
// less than 3 Digits
public class MMARNewBankAccountVOImpl extends NewBankAccountVOImpl
* This is the default constructor (do not remove)
public MMARNewBankAccountVOImpl()
public void initQuery()
if(!isExecuted())
executeQuery();
reset();
// Wrapper Method to validate Routing Number and Account Number
public void validateNewBankAccount()
OAApplicationModuleImpl oaapplicationmoduleimpl = (OAApplicationModuleImpl)getApplicationModule();
RowSetIterator rowsetiterator = createRowSetIterator("iter");
rowsetiterator.reset();
NewBankAccountVORowImpl newbankaccountvorowimpl = (NewBankAccountVORowImpl)rowsetiterator.next();
rowsetiterator.closeRowSetIterator();
OAException oaexception = null;
//object obj = null;
int i = validateRoutingNumber(newbankaccountvorowimpl.getStrippedRoutingNumber());
if(i == 0)
OAException oaexception1 = new OAException("AR", "ARI_INVALID_ROUTING_NUMBER");
if(oaexception == null)
oaexception = oaexception1;
else
oaexception.setNextException(oaexception1);
} else
if(i == 2)
OAException oaexception2 = new OAException("AR", "ARI_CREATE_BANK_ACCOUNT");
if(oaexception == null)
oaexception = oaexception2;
else
oaexception.setNextException(oaexception2);
// Added by VEERENDRA KODALLI to limit addition of New Bank Account with Minimum 3 Digits
if(validateBankAccountNumber(newbankaccountvorowimpl.getStrippedBankAccountNumber()))
// Define Exception with FND Message MMARI_INVALID_BA_NUMBER
OAException oaexception4 = new OAException("AR", "MMARI_INVALID_BA_NUMBER");
if(oaexception == null)
oaexception = oaexception4;
else
oaexception.setNextException(oaexception4);
// Method to Validate if Entered Account Number and Routing Number Combination already exist
if(validateDuplicateBankAccountNumber(newbankaccountvorowimpl.getStrippedBankAccountNumber(), newbankaccountvorowimpl.getStrippedRoutingNumber(), newbankaccountvorowimpl.getAccountHolderName()))
OAException oaexception3 = new OAException("AR", "ARI_DUPLICATE_BA_NUMBER");
if(oaexception == null)
oaexception = oaexception3;
else
oaexception.setNextException(oaexception3);
if(oaexception != null)
oaexception.setApplicationModule(oaapplicationmoduleimpl);
throw oaexception;
} else
return;
// Method to Validate Routing Number
public int validateRoutingNumber(String s)
boolean flag = PaymentUtilities.checkDigits(s);
if(!flag)
return 0;
OAApplicationModuleImpl oaapplicationmoduleimpl = (OAApplicationModuleImpl)getApplicationModule();
OADBTransaction oadbtransaction = (OADBTransaction)oaapplicationmoduleimpl.getDBTransaction();
if(oadbtransaction.isLoggingEnabled(2))
oadbtransaction.writeDiagnostics(this, "Start validateRoutingNumber", 2);
String s1 = "BEGIN :1 := ARP_BANK_DIRECTORY.is_routing_number_valid(:2,:3); END;";
OracleCallableStatement oraclecallablestatement = (OracleCallableStatement)oadbtransaction.createCallableStatement(s1, 1);
int i = 0;
try
oraclecallablestatement.registerOutParameter(1, -5, 38, 38);
oraclecallablestatement.setString(2, s);
oraclecallablestatement.setString(3, "ABA");
oraclecallablestatement.execute();
i = oraclecallablestatement.getInt(1);
catch(Exception exception1)
exception1.printStackTrace();
throw OAException.wrapperException(exception1);
finally
try
oraclecallablestatement.close();
catch(Exception exception2)
throw OAException.wrapperException(exception2);
// Debug Message
if(oadbtransaction.isLoggingEnabled(2))
oadbtransaction.writeDiagnostics(this, "End validateRoutingNumber", 2);
return i;
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public boolean validateDuplicateBankAccountNumber(String s, String s1, String s2)
OAApplicationModuleImpl oaapplicationmoduleimpl = (OAApplicationModuleImpl)getApplicationModule();
OADBTransaction oadbtransaction = (OADBTransaction)oaapplicationmoduleimpl.getDBTransaction();
if(oadbtransaction.isLoggingEnabled(2))
// Debug Message
oadbtransaction.writeDiagnostics(this, "Start validateDuplicateBankAccountNumber", 2);
String s3 = "BEGIN :1 := AR_IREC_PAYMENTS.is_bank_account_duplicate(:2,:3,:4); END;";
OracleCallableStatement oraclecallablestatement = (OracleCallableStatement)oadbtransaction.createCallableStatement(s3, 1);
boolean flag = true;
try
oraclecallablestatement.registerOutParameter(1, -5, 38, 38);
oraclecallablestatement.setString(2, s);
oraclecallablestatement.setString(3, s1);
oraclecallablestatement.setString(4, s2);
oraclecallablestatement.execute();
Number number = new Number(oraclecallablestatement.getLong(1));
if(number.equals(new Number("0")))
flag = false;
else
flag = true;
catch(Exception exception1)
exception1.printStackTrace();
throw OAException.wrapperException(exception1);
finally
try
oraclecallablestatement.close();
catch(Exception exception2)
throw OAException.wrapperException(exception2);
// Debug Message
if(oadbtransaction.isLoggingEnabled(2))
oadbtransaction.writeDiagnostics(this, "End validateDuplicateBankAccountNumber", 2);
return flag;
public boolean validateBankAccountNumber(String s)
OAApplicationModuleImpl oaapplicationmoduleimpl = (OAApplicationModuleImpl)getApplicationModule();
OADBTransaction oadbtransaction = (OADBTransaction)oaapplicationmoduleimpl.getDBTransaction();
// Debug Message
if(oadbtransaction.isLoggingEnabled(2))
oadbtransaction.writeDiagnostics(this, "Start validateBankAccountNumber", 2);
boolean flag = true;
try
// Check if the Account Number Length is less than 3 Digits
if(s.length() < 3)
flag = true;
// Debug Message
if(oadbtransaction.isLoggingEnabled(2))
oadbtransaction.writeDiagnostics(this, "Account Number Less than 3 Digits!", 2);
else
// Debug Message
if(oadbtransaction.isLoggingEnabled(2))
oadbtransaction.writeDiagnostics(this, "Account Number greater than 3 Digits!", 2);
flag = false;
//return PaymentUtilities.checkDigits(s);
catch (Exception exception4)
//if(oadbtransaction.isLoggingEnabled(2))
//oadbtransaction.writeDiagnostics(this, "Entered Catch", 2);
throw OAException.wrapperException(exception4);
if(oadbtransaction.isLoggingEnabled(2))
// Debug Message
oadbtransaction.writeDiagnostics(this, "End validateBankAccountNumber", 2);
return flag;
public static final String RCS_ID = "$Header: NewBankAccountVOImpl.java 115.8 2008/07/21 13:49:37 nkanchan noship $";
public static final boolean RCS_ID_RECORDED = VersionInfo.recordClassVersion("$Header: NewBankAccountVOImpl.java 115.8 2008/07/21 13:49:37 nkanchan noship $", "oracle.apps.ar.irec.accountDetails.pay.server");
I did compile the Java File and also the JPX import. It was all successful. I tested the code and it worked as expected. Now I see an exception on the page when I click the Pay button stating "No Method Signature No Method Signature - initQuery".
The error do not come when I take out my substitution. Any one know what might be the reason for above issue. I have no idea why all of a sudden it stopped working and checked all standard filles but none got changed.
Any pointers towards to resolve the same would be appreciable.
Thanks in Advance,
Veerendra

Uma,
try to delete all class files, recompile and run! Also, check if any CO is not extended other than from OAControllerImpl, although it would not be generally.
--Mukul

Problems deploying application with updated method signatures on WLS8.1

Hi,
I have an jar file under applications which I have deployed fine on WLS 8.1 in the past. I changed the method signature on one of the EJB classes in the jar. One of the parameters now takes a different Java class type. I have recompiled everyone and repackaged the jar but when I try to deploy the jar it gives me an error because the the local interface of the EJB does not have the old Java class parameter type.
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Can you show me the error you receive?
Another simple test would be to deploy your application to a new, empty
server.
You can create a new domain as easy as this:
mkdir testDomain;
cd testDomain;
java weblogic.Server
Type in the username/password that you want and answer 'Yes' when it
asks if you want to create a new domain.
Try deploying your jar to this new domain, and let me know if it still
fails.
-- Rob
Jeff Dooley wrote:
Hi,
I have an jar file under applications which I have deployed fine on WLS 8.1 in the past. I changed the method signature on one of the EJB classes in the jar. One of the parameters now takes a different Java class type. I have recompiled everyone and repackaged the jar but when I try to deploy the jar it gives me an error because the the local interface of the EJB does not have the old Java class parameter type.
I have checked the jar, classes in the jar, and the ejb-jar.xml and weblogic-ejb-jar.xml in the jar and it is looks fine. I have cleaned out my server deployment directories and verified the classpath in case the older jar was in there and everything looks OK. It seems for some reason 8.1 is caching the old ejb-jar.xml or somehow is remembering the old method signature and will not process the updated jar. Has anyone seen anything like this?
Thanks for any help or recommendations

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AS3:
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                   lake_mc.addEventListener(MouseEvent.MOUSE_UP, stdrag);
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                   var mountn_mc:mountn_png=new mountn_png();
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                  citywide_mc.addEventListener(MouseEvent.MOUSE_UP, stdrag);
          if (event.currentTarget.name=="bg_load7") {
                   var downtown_mc:downtown_png=new downtown_png();
                   addChild(downtown_mc);
                   downtown_mc.x=downtown_mc.mouseX;
                   downtown_mc.y=downtown_mc.mouseY;
                   downtown_mc.name="downtown_duplicate"+downtown_inc;
                   downtown_inc++;
                   downtown_mc.startDrag(false);
                  downtown_mc.addEventListener(MouseEvent.MOUSE_UP, stdrag);
          if (event.currentTarget.name=="bg_load8") {
                   var powerlines_mc:powerlines_png=new powerlines_png();
                   addChild(powerlines_mc);
                   powerlines_mc.x=powerlines_mc.mouseX;
                   powerlines_mc.y=powerlines_mc.mouseY;
                   powerlines_mc.name="powerlines_duplicate"+powerlines_inc;
                   powerlines_inc++;
                   powerlines_mc.startDrag(false);
                  powerlines_mc.addEventListener(MouseEvent.MOUSE_UP, stdrag);
          if (event.currentTarget.name=="bg_load9") {
                   var tropical_mc:tropical_png=new tropical_png();
                   addChild(tropical_mc);
                   tropical_mc.x=tropical_mc.mouseX;
                   tropical_mc.y=tropical_mc.mouseY;
                   tropical_mc.name="tropical_duplicate"+tropical_inc;
                   tropical_inc++;
                   tropical_mc.startDrag(false);
                  tropical_mc.addEventListener(MouseEvent.MOUSE_UP, stdrag);
          if (event.currentTarget.name=="bg_load10") {
                   var waters_mc:waters_png=new waters_png();
                   addChild(waters_mc);
                   waters_mc.x=waters_mc.mouseX;
                   waters_mc.y=waters_mc.mouseY;
                   waters_mc.name="waters_duplicate"+waterthumb_inc;
                   waterthumb_inc++;
                   waters_mc.startDrag(false);
                  waters_mc.addEventListener(MouseEvent.MOUSE_UP, stdrag);
Please suggest me if any one.
Regards,
Viji. S

Post AS3 questions in the AS3 forum, not the AS1/2 forum.

Deciding when to use "final" in method signatures

Please consider this source code:
public void foo(final Set<String> set) { ... }People who use this class don't need to know that the "set" reference is "final", right?
Edited by: dpxqb on Apr 30, 2010 3:28 AM

Kayaman wrote:
They should be implicitly final so there would be no need for questions like this.I don't understand what that means.
Or does someone here admit to having a habit of reassigning the parameters?I don't understand. I do it when it needs doing. Here is an example where I re-assigned the reference in the method signature:
void foo(Writer w) {
int i = 0;
boolean hit = false;
BufferedWriter bw = new BufferedWriter(w);
Set<String> set = new HashSet<String>();
bw.write(c);
w.write(c); // no exception thrown. the object on the other end of the Writer will act weird
// which further masks the bug.
}There are two working Writers going to the same location. There is no reason for this, it makes no sense, and it is a bug waiting to happen.
This is how I got my BufferedWriter. Reassign the initial reference:
void foo(Writer w) {
if(! (w instanceof BufferedWriter)) {
w = new BufferedWriter(w);
}The only way to write is via a single object. It just prevents me from doing something stupid. I feel safer by eliminating unused references.

Changing exception clause in method signature when overwriting a method

Hi,
I stumbled upon a situation by accident and am not really clear on the details surrounding it. A short description:
Say there is some API with interfaces Foo and Bar as follows:
public interface Foo {
   void test() throws Exception;
public interface Bar extends Foo {
   void test();
}Now, I find it strange that method test() for interface Bar does not need to define Exception in its throws clause. When I first started with Java I was using Java 1.4.2; I now use Java 1.6. I cannot remember ever reading about this before and I have been unable to find an explanation or tutorial on how (or why) this works.
Consider a more practical example:
Say there is an API that uses RMI and defines interfaces as follwows:
public interface RemoteHelper extends Remote {
   public Object select(int uid) throws RemoteException;
public interface LocalHelper extends RemoteHelper {
   public Object select(int uid);
}As per the RMI spec every method defined in a Remote interface must define RemoteException in its throws clause. The LocalHelper cannot be exported remotely (this will fail at runtime due to select() in LocalHelper not having RemoteException in its clause if I remember correctly).
However, an implementing class for LocalHelper could represent a wrapper class for RemoteHelper, like this:
public class Helper implements LocalHelper {
   private final RemoteHelper helper;
   public Helper(RemoteHelper helper) {
      this.helper = helper;
   public Object select(int id) {
      try {
         return (this.helper.select(id));
      } catch(RemoteException e) {
         // invoke app failure mechanism
}This can uncouple an app from RMI dependancy. In more practical words: consider a webapp that contains two Servlets: a "startup" servlet and an "invocation" servlet. The startup servlet does nothing (always returns Method Not Allowed, default behaviour of HttpServlet), except locate an RMI Registry upon startup and look up some object bound to it. It can then make this object accessible to other classes through whatever means (i.e. a singleton Engine class).
The invocation servlet does nothing upon startup, but simply calls some method on the previously acquired remote object. However, the invocation servlet does not need to know that the object is remote. Therefore, if the startup servlet wraps the remote object in another object (using the idea described before) then the invocation servlet is effectively removed from the RMI dependancy. The wrapper class can invoke some sort of failure mechanism upon the singleton engine (i.e. removing the remote object from memory) and optionally throw some other (optionally checked) exception (i.e. IllegalStateException) to the invocation servlet.
In this way, the invocation servlet is not bound to RMI, there can be a single point where RemoteExceptions are handled and an unchecked exception (i.e. IllegalStateException) can be handled by the Servlet API through an exception error page, displaying a "Service Unavailable" message.
Sorry for all this extensive text; I just typed out some thoughts. In short, my question is how and why can the throws clause change when overwriting a method? It's nothing I need though, except for the clarity (e.g. is this a bad practice to do?) and was more of an observation than a question.
PS: Unless I'm mistaken, this is basically called the "Adapter" or "Bridge" (not sure which one it is) pattern (or a close adaptation to it) right (where one class is written to provide access to another class where the method signature is different)?
Thanks for reading,
Yuthura

Yuthura wrote:
I know it may throw any checked exception, but I'm pretty certain that an interface that extends java.rmi.Remote must include at least java.rmi.RemoteException in its throws clause (unless the spec has changed in Java 1.5/1.6).No.
A method can always throw fewer exceptions than the one it's overriding. RMI has nothing to do with it.
See Deitel & Deilte Advanced Java 2 Platform How To Program, 1st Ed. (ISBN 0-13-089650-1), page 793 (sorry, I couldn't find the RMI spec quick enough). Quote: "Each method in a Remote interface must have a throws clause that indicates that the method can throw RemoteException".Which means that there's always a possibility of RemoteException being thrown. That's a different issue. It's not becusae the parent class can throw RE. Rather, it's because some step that will always be followed is declared to throw RE.
I later also noticed I could not add other checked exceptions, which made sense indeed. Your explanation made perfect sense now that I heard (read) it. But just to humour my curousity, has this always been possible? Yes, Java has always worked that way.
PS: The overwriting/-riding was a grammatical typo (English is not my native language), but I meant to say what you said.No problem. Minor detail. It's a common mistake, but I always try to encourage proper terminology.

Method signature of a two dimensional array of an object

Hi,
Does anyone know how to set the method signature of a two dimensional array of an object (e.g. : String[][]).
Thank you.

using javap for the following function:
public int testFunction(String myStr[][]);
public int disconnectServer(java.lang.String[][]);
/* ([[Ljava/lang/String;)I */
so the signature is:
([[Ljava/lang/String;)I

Doubt about generic method

i have a generic method has shown below
public static <E extends Number> <E>process(E list){
List<Interger> output = new ArrayList<Interger>(); or List<Number> output = new ArrayList<Number>();
return output ;
if delcare the output variable using Interger or Number . when i am returning the output . it is showing me compiler error and it suggests me to add cast List<E>. Why i not able understand. please clarify my doubt.
Thanks
Sura.Maruthi
Edited by: sura.maruthi on Sep 21, 2008 9:48 PM

Your method declaration is garbled; there can be only one <...> clause, eg
public static <E extends Number> E process(E list);This declaration says that for any subclass E of Number, the method process takes a single E instance (called list!?) and returns a single E instance. A valid implementation would be
return list;I'm guessing you want the parameter to have type List<E>?. Like this:
public static <E extends Number> E process(List<E> list);This declaration says that for any subclass E of Number, the method process takes a list of E's and returns a single E instance. A valid implementation would be
return list.get(0);Or perhaps you also want to return a list of numbers?
public static <E extends Number> List<E> process(List<E> list);This declaration says that for any subclass E of Number, the method process takes a list of E's and returns another list of E's. A valid implementation would be
return list;Note that you cannot just return a list of Integers or Floats, because your generic method must work for any subclass of Number, and you're promising to return back a list of the same type as the argument passed in.
Edited by: nygaard on Sep 22, 2008 10:05 AM

Generic method signatures

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