Re: [OT] More Java's generic type parameters are not reified...
the first time I used genericsuperclass() was in generic daos after
reading https://www.hibernate.org/328.html,
though it has it's own quirks, it doesn't apply every where ..
abstract modifier in above code was needed,it's done so that one will
eventually subclass funnyfactory
and that genericsuperclass hack will work ..
apart from that one another simple way for retrieving the generic classtype
is intializing the class type in
constructor.
conditions apply ;)
--
regards,
Vineet Semwal
On Thu, Sep 17, 2009 at 4:13 AM, jWeekend jweekend_for...@cabouge.comwrote:
Since you can NOT do
class ST{S(){T t = new T();}} // broken
how would you create an object of type T somewhere in S? Think about this
before you read on ...
At the risk of reigniting the world-famous generics debates of yesteryear,
just as our noble core-developers regroup to start work on making 1.5 even
better than what is already the best Java web framework, I thought I'd share
the idea I suggested to one of our developers who was having a bad day with
generics (for several good reasons [1][2]) a couple of months ago, in case
you can make use of it somewhere, or, find an even more convoluted solution
- notice the innocent looking abstract modifier!
// not real code
// don't try this at home without adult supervision!
public abstract class FunnyFactoryT {
private T instance = null;
public T getInstance() {
if (instance == null) {
try {
final ParameterizedType gsc =
(ParameterizedType)getClass().getGenericSuperclass();
final ClassT typeT = (ClassT)
gsc.getActualTypeArguments()[0];
instance = typeT.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
return instance; }
}
...
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
FunnyFactoryPoint factory = new FunnyFactoryPoint() {};
factory .getInstance().x = 22;
factory .getInstance().y = 47;
assertEquals(new Point(22, 47), factory.getInstance());
}
}
Regards - Cemal jWeekend OO Java Technologies, Wicket Training and
Development http://jWeekend.com
[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html
[2]
http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.html
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Re: [OT] More Java's generic type parameters are not reified...
what happens if down the line the index of the type changes?: )
class FunnierFactoryA,B extends FunnyFactoryB
-igor
On Wed, Sep 16, 2009 at 3:43 PM, jWeekend jweekend_for...@cabouge.com wrote:
Since you can NOT do
class ST{S(){T t = new T();}} // broken
how would you create an object of type T somewhere in S? Think about this
before you read on ...
At the risk of reigniting the world-famous generics debates of yesteryear,
just as our noble core-developers regroup to start work on making 1.5 even
better than what is already the best Java web framework, I thought I'd share
the idea I suggested to one of our developers who was having a bad day with
generics (for several good reasons [1][2]) a couple of months ago, in case
you can make use of it somewhere, or, find an even more convoluted solution
- notice the innocent looking abstract modifier!
// not real code
// don't try this at home without adult supervision!
public abstract class FunnyFactoryT {
private T instance = null;
public T getInstance() {
if (instance == null) {
try {
final ParameterizedType gsc =
(ParameterizedType)getClass().getGenericSuperclass();
final ClassT typeT = (ClassT)
gsc.getActualTypeArguments()[0];
instance = typeT.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
return instance; }
}
...
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
FunnyFactoryPoint factory = new FunnyFactoryPoint() {};
factory .getInstance().x = 22;
factory .getInstance().y = 47;
assertEquals(new Point(22, 47), factory.getInstance());
}
}
Regards - Cemal jWeekend OO Java Technologies, Wicket Training and
Development http://jWeekend.com
[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html
[2]
http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.html
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Re: [OT] More Java's generic type parameters are not reified...
... or, if you subclass the subclass ...
In the form I gave it's very fragile - just a trick really, but it tells you
a bit about what is actually in the bytecode and contradicts (as
conclusively as using javap) what some would have you believe.
Regards - Cemal
jWeekend OO Java Technologies, Wicket Training and Development
http://jWeekend.com
igor.vaynberg wrote:
what happens if down the line the index of the type changes?: )
class FunnierFactoryA,B extends FunnyFactory
-igor
On Wed, Sep 16, 2009 at 3:43 PM, jWeekend jweekend_for...@cabouge.com
wrote:
Since you can NOT do
class ST{S(){T t = new T();}} // broken
how would you create an object of type T somewhere in S? Think about this
before you read on ...
At the risk of reigniting the world-famous generics debates of
yesteryear,
just as our noble core-developers regroup to start work on making 1.5
even
better than what is already the best Java web framework, I thought I'd
share
the idea I suggested to one of our developers who was having a bad day
with
generics (for several good reasons [1][2]) a couple of months ago, in
case
you can make use of it somewhere, or, find an even more convoluted
solution
- notice the innocent looking abstract modifier!
// not real code
// don't try this at home without adult supervision!
public abstract class FunnyFactoryT {
private T instance = null;
public T getInstance() {
if (instance == null) {
try {
final ParameterizedType gsc =
(ParameterizedType)getClass().getGenericSuperclass();
final ClassT typeT = (ClassT)
gsc.getActualTypeArguments()[0];
instance = typeT.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
return instance; }
}
...
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
FunnyFactoryPoint factory = new FunnyFactoryPoint() {};
factory .getInstance().x = 22;
factory .getInstance().y = 47;
assertEquals(new Point(22, 47), factory.getInstance());
}
}
Regards - Cemal jWeekend OO Java Technologies, Wicket Training and
Development http://jWeekend.com
[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html
[2]
http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.html
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Re: [OT] More Java's generic type parameters are not reified...
Vineet ,
Yes, this is a technique that, carefully and properly used, could help in
building a generic DAO.
Can you elaborate on intializing the class type in constructor. ?
Regards - Cemal
jWeekend
OO Java Technologies, Wicket Training and Development
http://jWeekend.com
vineet semwal wrote:
the first time I used genericsuperclass() was in generic daos after
reading https://www.hibernate.org/328.html,
though it has it's own quirks, it doesn't apply every where ..
abstract modifier in above code was needed,it's done so that one will
eventually subclass funnyfactory
and that genericsuperclass hack will work ..
apart from that one another simple way for retrieving the generic
classtype
is intializing the class type in
constructor.
conditions apply ;)
--
regards,
Vineet Semwal
On Thu, Sep 17, 2009 at 4:13 AM, jWeekend
jweekend_for...@cabouge.comwrote:
Since you can NOT do
class ST{S(){T t = new T();}} // broken
how would you create an object of type T somewhere in S? Think about this
before you read on ...
At the risk of reigniting the world-famous generics debates of
yesteryear,
just as our noble core-developers regroup to start work on making 1.5
even
better than what is already the best Java web framework, I thought I'd
share
the idea I suggested to one of our developers who was having a bad day
with
generics (for several good reasons [1][2]) a couple of months ago, in
case
you can make use of it somewhere, or, find an even more convoluted
solution
- notice the innocent looking abstract modifier!
// not real code
// don't try this at home without adult supervision!
public abstract class FunnyFactoryT {
private T instance = null;
public T getInstance() {
if (instance == null) {
try {
final ParameterizedType gsc =
(ParameterizedType)getClass().getGenericSuperclass();
final ClassT typeT = (ClassT)
gsc.getActualTypeArguments()[0];
instance = typeT.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
return instance; }
}
...
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
FunnyFactoryPoint factory = new FunnyFactoryPoint() {};
factory .getInstance().x = 22;
factory .getInstance().y = 47;
assertEquals(new Point(22, 47), factory.getInstance());
}
}
Regards - Cemal jWeekend OO Java Technologies, Wicket Training and
Development http://jWeekend.com
[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html
[2]
http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.html
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RE: [OT] More Java's generic type parameters are not reified...
Another related article by Gafter:
http://gafter.blogspot.com/2006/12/super-type-tokens.html
class ST{
S() {
// T t = new T();
T t = new TypeReferenceT() {}.newInstance();
}
}
The unittest would then look like this.
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
Point instance = new TypeReferencePoint() {}.newInstance();
instance.x = 22;
instance.y = 47;
assertEquals(new Point(22, 47), instance);
}
}
Looks pretty powerful to me ;-)
Regards
misl
-Oorspronkelijk bericht-
Van: jWeekend [mailto:jweekend_for...@cabouge.com]
Verzonden: donderdag 17 september 2009 0:44
Aan: users@wicket.apache.org
Onderwerp: [OT] More Java's generic type parameters are not reified...
Since you can NOT do
class ST{S(){T t = new T();}} // broken
how would you create an object of type T somewhere in S? Think about
this before you read on ...
At the risk of reigniting the world-famous generics debates of
yesteryear, just as our noble core-developers regroup to start work on
making 1.5 even better than what is already the best Java web framework,
I thought I'd share the idea I suggested to one of our developers who
was having a bad day with generics (for several good reasons [1][2]) a
couple of months ago, in case you can make use of it somewhere, or, find
an even more convoluted solution - notice the innocent looking abstract
modifier!
// not real code
// don't try this at home without adult supervision!
public abstract class FunnyFactoryT {
private T instance = null;
public T getInstance() {
if (instance == null) {
try {
final ParameterizedType gsc =
(ParameterizedType)getClass().getGenericSuperclass();
final ClassT typeT =
(ClassT) gsc.getActualTypeArguments()[0];
instance = typeT.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
return instance;
}
}
...
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
FunnyFactoryPoint factory = new FunnyFactoryPoint() {};
factory .getInstance().x = 22;
factory .getInstance().y = 47;
assertEquals(new Point(22, 47), factory.getInstance());
}
}
Regards - Cemal
jWeekend
OO Java Technologies, Wicket Training and Development
http://jWeekend.com
[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html
[2]
http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.ht
ml
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RE: [OT] More Java's generic type parameters are not reified...
Yes indeed! This (see Neal Gafter's code below) is neat and getting much
closer to being actually usable, as long as its implementation is hidden
well away. I'd probably mark some of those methods final too (it's a shame
the class itself can't be - a subclasser could mess up the type parameter
list, as per Igor's post).
public abstract class TypeReferenceT
private final Type type;
private volatile Constructor? constructor;
protected TypeReference() {
Type superclass = getClass().getGenericSuperclass();
if (superclass instanceof Class) {
throw new RuntimeException(Missing type parameter.);
}
this.type = ((ParameterizedType)
superclass).getActualTypeArguments()[0];
}
/**
* Instantiates a new instance of {...@code T} using the default, no-arg
* constructor.
*/
@SuppressWarnings(unchecked)
public T newInstance() throws NoSuchMethodException,
IllegalAccessException, InvocationTargetException,
InstantiationException {
if (constructor == null) {
Class? rawType = type instanceof Class? ? (Class?) type :
(Class?) ((ParameterizedType) type)
.getRawType();
constructor = rawType.getConstructor();
}
return (T) constructor.newInstance();
}
/**
* Gets the referenced type.
*/
public Type getType() {
return this.type;
}
public static void main(String[] args) throws Exception {
ListString l1 = new TypeReferenceArrayListString() {
}.newInstance();
List l2 = new TypeReferenceArrayList() {
}.newInstance();
}
}
Regards - Cemal
jWeekend
OO Java Technologies, Wicket Training and Development
http://jWeekend.com
Minto.van.der.Sluis wrote:
Another related article by Gafter:
http://gafter.blogspot.com/2006/12/super-type-tokens.html
class ST{
S() {
// T t = new T();
T t = new TypeReferenceT() {}.newInstance();
}
}
The unittest would then look like this.
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
Point instance = new TypeReferencePoint() {}.newInstance();
instance.x = 22;
instance.y = 47;
assertEquals(new Point(22, 47), instance);
}
}
Looks pretty powerful to me ;-)
Regards
misl
-Oorspronkelijk bericht-
Van: jWeekend [mailto:jweekend_for...@cabouge.com]
Verzonden: donderdag 17 september 2009 0:44
Aan: users@wicket.apache.org
Onderwerp: [OT] More Java's generic type parameters are not reified...
Since you can NOT do
class ST{S(){T t = new T();}} // broken
how would you create an object of type T somewhere in S? Think about
this before you read on ...
At the risk of reigniting the world-famous generics debates of
yesteryear, just as our noble core-developers regroup to start work on
making 1.5 even better than what is already the best Java web framework,
I thought I'd share the idea I suggested to one of our developers who
was having a bad day with generics (for several good reasons [1][2]) a
couple of months ago, in case you can make use of it somewhere, or, find
an even more convoluted solution - notice the innocent looking abstract
modifier!
// not real code
// don't try this at home without adult supervision!
public abstract class FunnyFactoryT {
private T instance = null;
public T getInstance() {
if (instance == null) {
try {
final ParameterizedType gsc =
(ParameterizedType)getClass().getGenericSuperclass();
final ClassT typeT =
(ClassT) gsc.getActualTypeArguments()[0];
instance = typeT.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
return instance;
}
}
...
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
FunnyFactoryPoint factory = new FunnyFactoryPoint() {};
factory .getInstance().x = 22;
factory .getInstance().y = 47;
assertEquals(new Point(22, 47), factory.getInstance());
}
}
Regards - Cemal
jWeekend
OO Java Technologies, Wicket Training and Development
http://jWeekend.com
[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html
[2]
http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.ht
ml
-
To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org
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=DISCLAIMER
De informatie in deze e-mail is vertrouwelijk en uitsluitend bestemd
voor de geadresseerde. Indien u niet de geadresseerde bent, wordt u
er hierbij op gewezen, dat u geen recht heeft
Re: [OT] More Java's generic type parameters are not reified...
I should have stated it clearly ..
i actually meant passing type Class in constructor itself like in following
code:-
class FunnyT {
private ClassTtypeClass;
public Funny(ClassTtypeClass){
this.typeClass=typeClass;
}
}
class FunnierT,R extends FunnyT{
private ClassTtypeClassT;
private ClassRtypeClassR;
public Funnier( ClassTtypeClassT,ClassRtypeClassR){
super(typeClassT);
this.typeClassT=typeClassT;
this.typeClassR=typeClassR;
}
}
--
regards,
Vineet Semwal
On Thu, Sep 17, 2009 at 2:58 PM, jWeekend jweekend_for...@cabouge.comwrote:
Vineet ,
Yes, this is a technique that, carefully and properly used, could help in
building a generic DAO.
Can you elaborate on intializing the class type in constructor. ?
Regards - Cemal
jWeekend
OO Java Technologies, Wicket Training and Development
http://jWeekend.com
vineet semwal wrote:
the first time I used genericsuperclass() was in generic daos after
reading https://www.hibernate.org/328.html,
though it has it's own quirks, it doesn't apply every where ..
abstract modifier in above code was needed,it's done so that one will
eventually subclass funnyfactory
and that genericsuperclass hack will work ..
apart from that one another simple way for retrieving the generic
classtype
is intializing the class type in
constructor.
conditions apply ;)
--
regards,
Vineet Semwal
On Thu, Sep 17, 2009 at 4:13 AM, jWeekend
jweekend_for...@cabouge.comwrote:
Since you can NOT do
class ST{S(){T t = new T();}} // broken
how would you create an object of type T somewhere in S? Think about
this
before you read on ...
At the risk of reigniting the world-famous generics debates of
yesteryear,
just as our noble core-developers regroup to start work on making 1.5
even
better than what is already the best Java web framework, I thought I'd
share
the idea I suggested to one of our developers who was having a bad day
with
generics (for several good reasons [1][2]) a couple of months ago, in
case
you can make use of it somewhere, or, find an even more convoluted
solution
- notice the innocent looking abstract modifier!
// not real code
// don't try this at home without adult supervision!
public abstract class FunnyFactoryT {
private T instance = null;
public T getInstance() {
if (instance == null) {
try {
final ParameterizedType gsc =
(ParameterizedType)getClass().getGenericSuperclass();
final ClassT typeT = (ClassT)
gsc.getActualTypeArguments()[0];
instance = typeT.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
return instance; }
}
...
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
FunnyFactoryPoint factory = new FunnyFactoryPoint() {};
factory .getInstance().x = 22;
factory .getInstance().y = 47;
assertEquals(new Point(22, 47), factory.getInstance());
}
}
Regards - Cemal jWeekend OO Java Technologies, Wicket Training and
Development http://jWeekend.com
[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html
[2]
http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.html
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Re: [OT] More Java's generic type parameters are not reified...
and using it in this way
Funnier Foo,Barfunnier=new FunnierFoo,Bar(Foo.class,Bar.class);
or
Funny Foofunny=new FunnyFoo(Foo.class);
--
regards,
Vineet Semwal
On Thu, Sep 17, 2009 at 8:16 PM, vineet semwal
vineetsemwal1...@gmail.comwrote:
I should have stated it clearly ..
i actually meant passing type Class in constructor itself like in
following code:-
class FunnyT {
private ClassTtypeClass;
public Funny(ClassTtypeClass){
this.typeClass=typeClass;
}
}
class FunnierT,R extends FunnyT{
private ClassTtypeClassT;
private ClassRtypeClassR;
public Funnier( ClassTtypeClassT,ClassRtypeClassR){
super(typeClassT);
this.typeClassT=typeClassT;
this.typeClassR=typeClassR;
}
}
--
regards,
Vineet Semwal
On Thu, Sep 17, 2009 at 2:58 PM, jWeekend jweekend_for...@cabouge.comwrote:
Vineet ,
Yes, this is a technique that, carefully and properly used, could help in
building a generic DAO.
Can you elaborate on intializing the class type in constructor. ?
Regards - Cemal
jWeekend
OO Java Technologies, Wicket Training and Development
http://jWeekend.com
vineet semwal wrote:
the first time I used genericsuperclass() was in generic daos after
reading https://www.hibernate.org/328.html,
though it has it's own quirks, it doesn't apply every where ..
abstract modifier in above code was needed,it's done so that one will
eventually subclass funnyfactory
and that genericsuperclass hack will work ..
apart from that one another simple way for retrieving the generic
classtype
is intializing the class type in
constructor.
conditions apply ;)
--
regards,
Vineet Semwal
On Thu, Sep 17, 2009 at 4:13 AM, jWeekend
jweekend_for...@cabouge.comwrote:
Since you can NOT do
class ST{S(){T t = new T();}} // broken
how would you create an object of type T somewhere in S? Think about
this
before you read on ...
At the risk of reigniting the world-famous generics debates of
yesteryear,
just as our noble core-developers regroup to start work on making 1.5
even
better than what is already the best Java web framework, I thought I'd
share
the idea I suggested to one of our developers who was having a bad day
with
generics (for several good reasons [1][2]) a couple of months ago, in
case
you can make use of it somewhere, or, find an even more convoluted
solution
- notice the innocent looking abstract modifier!
// not real code
// don't try this at home without adult supervision!
public abstract class FunnyFactoryT {
private T instance = null;
public T getInstance() {
if (instance == null) {
try {
final ParameterizedType gsc =
(ParameterizedType)getClass().getGenericSuperclass();
final ClassT typeT = (ClassT)
gsc.getActualTypeArguments()[0];
instance = typeT.newInstance();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
return instance; }
}
...
public class CreateInstanceOfTypeParameter {
@Test
public void testCreateInstanceOfTypeParameter() {
FunnyFactoryPoint factory = new FunnyFactoryPoint() {};
factory .getInstance().x = 22;
factory .getInstance().y = 47;
assertEquals(new Point(22, 47), factory.getInstance());
}
}
Regards - Cemal jWeekend OO Java Technologies, Wicket Training and
Development http://jWeekend.com
[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html
[2]
http://weblogs.java.net/blog/arnold/archive/2005/06/generics_consid_1.html
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