EOEnterpriseObjectClazz with interface

[Morris, Mark]

Hi all,

I ran into a simple case where a good old ObjC protocol would have worked fine, but Java provides only frustration. 😉

I wanted to require that a class that decides to implement a particular interface should as part of that interface implement a certain static method. No go in Java.

The implementing classes will always be subclasses of ERXGenericRecord, and a little searching uncovered the promising EOEnterpriseObjectsClazz approach. Right at the top it says:

In Java, static methods are similar to class methods in Objective-C, but one cannot use static methods in interfaces and static methods cannot be overridden by a subclass. Using the clazz pattern removes those limitations.

However, I didn’t see any examples of this use, and spent a little time but couldn’t figure it out. Are there any examples out there?

Thanks!
Mark

[Johann Werner]

Hi Mark,

have a look at BugTracker and its dependent framework BTBusinessLogic. That should you give some ideas. There are some more apps/frameworks in Wonder using that pattern, just have a look at the type hierarchy of the EOEnterpriseObjectClazz class (in Eclipse right click on the class name and select „Open Type Hierarchy“ from the context menu).

jw

Post by Morris, Mark
Hi all,
I ran into a simple case where a good old ObjC protocol would have worked fine, but Java provides only frustration. 😉
I wanted to require that a class that decides to implement a particular interface should as part of that interface implement a certain static method. No go in Java.
In Java, static methods are similar to class methods in Objective-C, but one cannot use static methods in interfaces and static methods cannot be overridden by a subclass. Using the clazz pattern removes those limitations.
However, I didn’t see any examples of this use, and spent a little time but couldn’t figure it out. Are there any examples out there?
Thanks!
Mark

[Morris, Mark]

Hallo Johann,

Thanks for the info. I do see how I could create a default implementation of the “static” method I’m expecting in our local EO superclass’s util inner class, and from then on know that it will be legal to call it from any of our subclasses. So that could work in this case.

In general though I still don’t see how, or if it’s even possible, to do what I was originally trying with the interface. For instance methods, I can just test “myClass instanceof myInterface” and know whether that class implements the methods. In ObjC, I could do the same with a protocol, but with instance and class methods. It seems like the description of the clazz paradigm is saying it makes that possible, but I’m just not understanding how that works.

Thanks again. TschÌß!
Mark

From: Johann Werner <***@posteo.de>
Date: Monday, November 19, 2018 at 1:37 AM
To: "Morris, Mark" <***@experian.com>
Cc: "Webobjects-***@lists.apple.com" <Webobjects-***@lists.apple.com>
Subject: Re: EOEnterpriseObjectClazz with interface

Hi Mark,

have a look at BugTracker and its dependent framework BTBusinessLogic. That should you give some ideas. There are some more apps/frameworks in Wonder using that pattern, just have a look at the type hierarchy of the EOEnterpriseObjectClazz class (in Eclipse right click on the class name and select „Open Type Hierarchy“ from the context menu).

jw


Am 19.11.2018 um 06:31 schrieb Morris, Mark <***@experian.com<mailto:***@experian.com>>:

Hi all,

I ran into a simple case where a good old ObjC protocol would have worked fine, but Java provides only frustration. 😉

I wanted to require that a class that decides to implement a particular interface should as part of that interface implement a certain static method. No go in Java.

The implementing classes will always be subclasses of ERXGenericRecord, and a little searching uncovered the promising EOEnterpriseObjectsClazz approach. Right at the top it says:

In Java, static methods are similar to class methods in Objective-C, but one cannot use static methods in interfaces and static methods cannot be overridden by a subclass. Using the clazz pattern removes those limitations.

However, I didn’t see any examples of this use, and spent a little time but couldn’t figure it out. Are there any examples out there?

Thanks!
Mark

[Johann Werner]

Hi Mark,

I think you have to tell us what exactly you want to achieve? Do you have an example?

With the EOEnterpriseObjectClazz you have a static instance within your class but this instance is
 an instance so you could put an „implements interface“ on it. Or if you just want to know if class A has a static clazz object you could create some empty interface (IHasClazzObject) as marker.

jw

Post by Morris, Mark
Hallo Johann,
Thanks for the info. I do see how I could create a default implementation of the “static” method I’m expecting in our local EO superclass’s util inner class, and from then on know that it will be legal to call it from any of our subclasses. So that could work in this case.
In general though I still don’t see how, or if it’s even possible, to do what I was originally trying with the interface. For instance methods, I can just test “myClass instanceof myInterface” and know whether that class implements the methods. In ObjC, I could do the same with a protocol, but with instance and class methods. It seems like the description of the clazz paradigm is saying it makes that possible, but I’m just not understanding how that works.
Thanks again. TschÌß!
Mark
Date: Monday, November 19, 2018 at 1:37 AM
Subject: Re: EOEnterpriseObjectClazz with interface
Hi Mark,
have a look at BugTracker and its dependent framework BTBusinessLogic. That should you give some ideas. There are some more apps/frameworks in Wonder using that pattern, just have a look at the type hierarchy of the EOEnterpriseObjectClazz class (in Eclipse right click on the class name and select „Open Type Hierarchy“ from the context menu).
jw
Hi all,
I ran into a simple case where a good old ObjC protocol would have worked fine, but Java provides only frustration. 😉
I wanted to require that a class that decides to implement a particular interface should as part of that interface implement a certain static method. No go in Java.
In Java, static methods are similar to class methods in Objective-C, but one cannot use static methods in interfaces and static methods cannot be overridden by a subclass. Using the clazz pattern removes those limitations.
However, I didn’t see any examples of this use, and spent a little time but couldn’t figure it out. Are there any examples out there?
Thanks!
Mark

[Morris, Mark]

Hi Johann,

Sure! Here’s a hypothetical.

Let’s say I have a WorkflowRoutable interface that defines a few instance methods. Now I can implement that interface on EOs that need to participate in workflow, and call those methods in my workflow processing without any trouble. Now let’s say there’s some useful information used when configuring workflow queues to be able to handle a particular entity, but I may not have any instances at that point. I would want to define a class method as part of my WorkflowRoutable interface, so that I can safely call that method to get that entity-specific workflow information.

Again, no problem in ObjC. But static methods can’t be in Java interfaces (at least in that way). Can the Clazz approach help with something like this?

What I do see that I could do using the EOEnterpriseObjectClazz approach is implement the “class” method in the superclass of all my EOs with perhaps a default implementation that returns null. Then on my entities participating in workflow, they could override that method to return useful information. But now *all* of my classes have that default implementation, so it’s not really a clean workaround
.

Thanks again!
Mark

From: Johann Werner <***@posteo.de>
Date: Tuesday, November 20, 2018 at 3:39 AM
To: "Morris, Mark" <***@experian.com>
Cc: "Webobjects-***@lists.apple.com" <Webobjects-***@lists.apple.com>
Subject: Re: EOEnterpriseObjectClazz with interface

Hi Mark,

I think you have to tell us what exactly you want to achieve? Do you have an example?

With the EOEnterpriseObjectClazz you have a static instance within your class but this instance is
 an instance so you could put an „implements interface“ on it. Or if you just want to know if class A has a static clazz object you could create some empty interface (IHasClazzObject) as marker.

jw


Am 19.11.2018 um 22:12 schrieb Morris, Mark <***@experian.com<mailto:***@experian.com>>:

Hallo Johann,

Thanks for the info. I do see how I could create a default implementation of the “static” method I’m expecting in our local EO superclass’s util inner class, and from then on know that it will be legal to call it from any of our subclasses. So that could work in this case.

In general though I still don’t see how, or if it’s even possible, to do what I was originally trying with the interface. For instance methods, I can just test “myClass instanceof myInterface” and know whether that class implements the methods. In ObjC, I could do the same with a protocol, but with instance and class methods. It seems like the description of the clazz paradigm is saying it makes that possible, but I’m just not understanding how that works.

Thanks again. TschÌß!
Mark

From: Johann Werner <***@posteo.de<mailto:***@posteo.de>>
Date: Monday, November 19, 2018 at 1:37 AM
To: "Morris, Mark" <***@experian.com<mailto:***@experian.com>>
Cc: "Webobjects-***@lists.apple.com<mailto:Webobjects-***@lists.apple.com>" <Webobjects-***@lists.apple.com<mailto:Webobjects-***@lists.apple.com>>
Subject: Re: EOEnterpriseObjectClazz with interface

Hi Mark,

have a look at BugTracker and its dependent framework BTBusinessLogic. That should you give some ideas. There are some more apps/frameworks in Wonder using that pattern, just have a look at the type hierarchy of the EOEnterpriseObjectClazz class (in Eclipse right click on the class name and select „Open Type Hierarchy“ from the context menu).

jw


Am 19.11.2018 um 06:31 schrieb Morris, Mark <***@experian.com<mailto:***@experian.com>>:

Hi all,

I ran into a simple case where a good old ObjC protocol would have worked fine, but Java provides only frustration. 😉

I wanted to require that a class that decides to implement a particular interface should as part of that interface implement a certain static method. No go in Java.

The implementing classes will always be subclasses of ERXGenericRecord, and a little searching uncovered the promising EOEnterpriseObjectsClazz approach. Right at the top it says:

In Java, static methods are similar to class methods in Objective-C, but one cannot use static methods in interfaces and static methods cannot be overridden by a subclass. Using the clazz pattern removes those limitations.

However, I didn’t see any examples of this use, and spent a little time but couldn’t figure it out. Are there any examples out there?

Thanks!
Mark

[Henrique Prange]

Hey Mark,

Even if Java allowed you to override static methods of an interface, you would still have problems to discover the classes that implement them in runtime. In the end, it doesn't matter if you remember to implement the static method in your subclass if you forget to call it somewhere else.

For this reason, the answer to your question must have two characteristics:

1. Subclasses of WorkflowRoutable must implement a method to provide useful information.

2. WorkflowRoutable types must be easily discoverable at runtime.

It turns out there's a Java construct that can help you in this case. You could create an enum of WorkflowRoutableTypes and require every subclass of WorkflowRoutable to implement a method that returns its type.The code I imagine looks like this:

interface WorkflowRoutable {
public static enum WorkflowRoutableType {
WORKFLOW_1 {
@Override
public String usefulInformation() {
return "useful information for workflow routable 1";
}
},
WORKFLOW_2 {
@Override
public String usefulInformation() {
return "useful information for workflow routable 2";
}
};

public abstract String usefulInformation();
}

...

/**
* Returns the type of this WorkflowRoutable. You need to create a new type whenever
* you implement this interface. See {@code WorkflowRoutableType} for details.
*/
WorkflowRoutableType type();
}

class Workflow1 implements WorkflowRoutable {
@Override
public WorkflowRoutableType type() {
return WorkflowRoutableType.WORKFLOW_1;
}
}

class Workflow2 implements WorkflowRoutable {
@Override
public WorkflowRoutableType type() {
return WorkflowRoutableType.WORKFLOW_2;
}
}

If you create a new Workflow3 class implementing the WorkflowRoutable interface, the compiler will require you to override the type method. As a result, you'll have to create a new enum type with its version of the useful information method.

One side effect of this solution is the ability to discover WorkflowRoutable types in runtime easily:

for (WorkflowRoutableType type : WorkflowRoutableType.values()) {
type.usefulInformation();
...
}

And then you kill two birds with one stone. ;)

Cheers,

HP

Post by Morris, Mark
Hi Johann,
Sure! Here’s a hypothetical.
Let’s say I have a WorkflowRoutable interface that defines a few instance methods. Now I can implement that interface on EOs that need to participate in workflow, and call those methods in my workflow processing without any trouble. Now let’s say there’s some useful information used when configuring workflow queues to be able to handle a particular entity, but I may not have any instances at that point. I would want to define a class method as part of my WorkflowRoutable interface, so that I can safely call that method to get that entity-specific workflow information.
Again, no problem in ObjC. But static methods can’t be in Java interfaces (at least in that way). Can the Clazz approach help with something like this?
What I do see that I could do using the EOEnterpriseObjectClazz approach is implement the “class” method in the superclass of all my EOs with perhaps a default implementation that returns null. Then on my entities participating in workflow, they could override that method to return useful information. But now *all* of my classes have that default implementation, so it’s not really a clean workaround
.
Thanks again!
Mark
Date: Tuesday, November 20, 2018 at 3:39 AM
Subject: Re: EOEnterpriseObjectClazz with interface
Hi Mark,
I think you have to tell us what exactly you want to achieve? Do you have an example?
With the EOEnterpriseObjectClazz you have a static instance within your class but this instance is
 an instance so you could put an „implements interface“ on it. Or if you just want to know if class A has a static clazz object you could create some empty interface (IHasClazzObject) as marker.
jw
Hallo Johann,
Thanks for the info. I do see how I could create a default implementation of the “static” method I’m expecting in our local EO superclass’s util inner class, and from then on know that it will be legal to call it from any of our subclasses. So that could work in this case.
In general though I still don’t see how, or if it’s even possible, to do what I was originally trying with the interface. For instance methods, I can just test “myClass instanceof myInterface” and know whether that class implements the methods. In ObjC, I could do the same with a protocol, but with instance and class methods. It seems like the description of the clazz paradigm is saying it makes that possible, but I’m just not understanding how that works.
Thanks again. TschÌß!
Mark
Date: Monday, November 19, 2018 at 1:37 AM
Subject: Re: EOEnterpriseObjectClazz with interface
Hi Mark,
have a look at BugTracker and its dependent framework BTBusinessLogic. That should you give some ideas. There are some more apps/frameworks in Wonder using that pattern, just have a look at the type hierarchy of the EOEnterpriseObjectClazz class (in Eclipse right click on the class name and select „Open Type Hierarchy“ from the context menu).
jw
Hi all,
I ran into a simple case where a good old ObjC protocol would have worked fine, but Java provides only frustration. 😉
I wanted to require that a class that decides to implement a particular interface should as part of that interface implement a certain static method. No go in Java.
In Java, static methods are similar to class methods in Objective-C, but one cannot use static methods in interfaces and static methods cannot be overridden by a subclass. Using the clazz pattern removes those limitations.
However, I didn’t see any examples of this use, and spent a little time but couldn’t figure it out. Are there any examples out there?
Thanks!
Mark
_______________________________________________
Do not post admin requests to the list. They will be ignored.
https://lists.apple.com/mailman/options/webobjects-dev/hprange%40gmail.com

[Morris, Mark]

Hi Henrique,

That’s cool, I hadn’t considered how an enum and an interface could work together like that. ☺

In my particular case this could work. Another idea I had is using the EOEntity’s userInfo dictionary to store the relevant distinguishing information. But it doesn’t seem as clean as just adding the method to the interface, from an object-oriented / business logic encapsulation point of view. It seemed like that capability was implied by the class comments of EOEnterpriseObjectClazz, but perhaps it doesn’t quite go that far.

Thanks!
Mark

From: Henrique Prange <***@gmail.com>
Date: Tuesday, November 20, 2018 at 8:26 PM
To: "Morris, Mark" <***@experian.com>
Cc: "Webobjects-***@lists.apple.com" <Webobjects-***@lists.apple.com>
Subject: Re: EOEnterpriseObjectClazz with interface

Hey Mark,

Even if Java allowed you to override static methods of an interface, you would still have problems to discover the classes that implement them in runtime. In the end, it doesn't matter if you remember to implement the static method in your subclass if you forget to call it somewhere else.

For this reason, the answer to your question must have two characteristics:

1. Subclasses of WorkflowRoutable must implement a method to provide useful information.

2. WorkflowRoutable types must be easily discoverable at runtime.

It turns out there's a Java construct that can help you in this case. You could create an enum of WorkflowRoutableTypes and require every subclass of WorkflowRoutable to implement a method that returns its type.The code I imagine looks like this:

interface WorkflowRoutable {
public static enum WorkflowRoutableType {
WORKFLOW_1 {
@Override
public String usefulInformation() {
return "useful information for workflow routable 1";
}
},
WORKFLOW_2 {
@Override
public String usefulInformation() {
return "useful information for workflow routable 2";
}
};

public abstract String usefulInformation();
}

...

/**
* Returns the type of this WorkflowRoutable. You need to create a new type whenever
* you implement this interface. See {@code WorkflowRoutableType} for details.
*/
WorkflowRoutableType type();
}

class Workflow1 implements WorkflowRoutable {
@Override
public WorkflowRoutableType type() {
return WorkflowRoutableType.WORKFLOW_1;
}
}

class Workflow2 implements WorkflowRoutable {
@Override
public WorkflowRoutableType type() {
return WorkflowRoutableType.WORKFLOW_2;
}
}

If you create a new Workflow3 class implementing the WorkflowRoutable interface, the compiler will require you to override the type method. As a result, you'll have to create a new enum type with its version of the useful information method.

One side effect of this solution is the ability to discover WorkflowRoutable types in runtime easily:

for (WorkflowRoutableType type : WorkflowRoutableType.values()) {
type.usefulInformation();
...
}

And then you kill two birds with one stone. ;)

Cheers,

HP


On Nov 20, 2018, at 9:50 PM, Morris, Mark <***@experian.com<mailto:***@experian.com>> wrote:

Hi Johann,

Sure! Here’s a hypothetical.

Let’s say I have a WorkflowRoutable interface that defines a few instance methods. Now I can implement that interface on EOs that need to participate in workflow, and call those methods in my workflow processing without any trouble. Now let’s say there’s some useful information used when configuring workflow queues to be able to handle a particular entity, but I may not have any instances at that point. I would want to define a class method as part of my WorkflowRoutable interface, so that I can safely call that method to get that entity-specific workflow information.

Again, no problem in ObjC. But static methods can’t be in Java interfaces (at least in that way). Can the Clazz approach help with something like this?

What I do see that I could do using the EOEnterpriseObjectClazz approach is implement the “class” method in the superclass of all my EOs with perhaps a default implementation that returns null. Then on my entities participating in workflow, they could override that method to return useful information. But now *all* of my classes have that default implementation, so it’s not really a clean workaround
.

Thanks again!
Mark

From: Johann Werner <***@posteo.de<mailto:***@posteo.de>>
Date: Tuesday, November 20, 2018 at 3:39 AM
To: "Morris, Mark" <***@experian.com<mailto:***@experian.com>>
Cc: "Webobjects-***@lists.apple.com<mailto:Webobjects-***@lists.apple.com>" <Webobjects-***@lists.apple.com<mailto:Webobjects-***@lists.apple.com>>
Subject: Re: EOEnterpriseObjectClazz with interface

Hi Mark,

I think you have to tell us what exactly you want to achieve? Do you have an example?

With the EOEnterpriseObjectClazz you have a static instance within your class but this instance is
 an instance so you could put an „implements interface“ on it. Or if you just want to know if class A has a static clazz object you could create some empty interface (IHasClazzObject) as marker.

jw


Am 19.11.2018 um 22:12 schrieb Morris, Mark <***@experian.com<mailto:***@experian.com>>:

Hallo Johann,

Thanks for the info. I do see how I could create a default implementation of the “static” method I’m expecting in our local EO superclass’s util inner class, and from then on know that it will be legal to call it from any of our subclasses. So that could work in this case.

In general though I still don’t see how, or if it’s even possible, to do what I was originally trying with the interface. For instance methods, I can just test “myClass instanceof myInterface” and know whether that class implements the methods. In ObjC, I could do the same with a protocol, but with instance and class methods. It seems like the description of the clazz paradigm is saying it makes that possible, but I’m just not understanding how that works.

Thanks again. TschÌß!
Mark

From: Johann Werner <***@posteo.de<mailto:***@posteo.de>>
Date: Monday, November 19, 2018 at 1:37 AM
To: "Morris, Mark" <***@experian.com<mailto:***@experian.com>>
Cc: "Webobjects-***@lists.apple.com<mailto:Webobjects-***@lists.apple.com>" <Webobjects-***@lists.apple.com<mailto:Webobjects-***@lists.apple.com>>
Subject: Re: EOEnterpriseObjectClazz with interface

Hi Mark,

have a look at BugTracker and its dependent framework BTBusinessLogic. That should you give some ideas. There are some more apps/frameworks in Wonder using that pattern, just have a look at the type hierarchy of the EOEnterpriseObjectClazz class (in Eclipse right click on the class name and select „Open Type Hierarchy“ from the context menu).

jw


Am 19.11.2018 um 06:31 schrieb Morris, Mark <***@experian.com<mailto:***@experian.com>>:

Hi all,

I ran into a simple case where a good old ObjC protocol would have worked fine, but Java provides only frustration. 😉

I wanted to require that a class that decides to implement a particular interface should as part of that interface implement a certain static method. No go in Java.

The implementing classes will always be subclasses of ERXGenericRecord, and a little searching uncovered the promising EOEnterpriseObjectsClazz approach. Right at the top it says:

In Java, static methods are similar to class methods in Objective-C, but one cannot use static methods in interfaces and static methods cannot be overridden by a subclass. Using the clazz pattern removes those limitations.

However, I didn’t see any examples of this use, and spent a little time but couldn’t figure it out. Are there any examples out there?

Thanks!
Mark

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