I have some legacy code which will do:
MyInterface obj = new MyImpl
I'd like to intercept the creation of MyImpl and return another object say MyOtherImpl
Is it doable?
Thanks
As I have explained in my answer your other question, this does not work with sibling classes, only with subclasses.
Related
I'm setting up a Method call from a class
DATA: r_info TYPE REF TO zcl_sv_job_offline_ctrl.
CALL METHOD r_info->create
EXPORTING
is_data = lr_test_record.
And receiving the following errors:
CX_SY_REF_IS_INITAL
You are trying to access a component with a 'ZERO' object reference (points to nothing). Variable: "R_INFO".
Am I missing something?
You missed to create the object.
so you need to to:
create object r_info.
or
r_info = new zcl_sv_job_offline_ctrl( ).
or if there is a "factory method" ( what your 'create' method indicates )
r_info = zcl_sv_job_offline_ctrl=>create( is_data = lr_test_record ).
Your Exception tells you that the reference ( r_info ) is not connected with an object on the heap. So you need to do one of the above steps and then it should work. ( depending on your class )
Sorry, I don't have the rep to comment just yet...
I notice that your class is a Z so I'm wondering if you are trying to create a singleton class. In which case. Your 'Create' should be static. Your Constructor private and your Instance in a private attribute.
From the other comments, I agree, your question is missing some key details to provide an accurate answer.
If IO_DISPATCHER is part of the constructor and you are unable to pass a value, you need to dig a little deeper into the purpose of the class. See if you can give it what it wants. Try a 'where used' and check out the other usages of the class. You might find you are looking at the wrong class, or at least approaching from the wrong direction.
If create is some method on the class and it is not static then you will never get it to work until you create an instance of the class.
Another thought that comes to mind is that you might be in the right place and just doing the wrong thing. Check your globals to see if there is already an instance of the class and you are trying to access something via declaration as data rather than using the global instance??
All guess work without more details.
Thanks all.
The solution was simply to instantiate the parent classes (properly), enabled me to instantiate the class in question.
As stated in the title - can somebody give me an example of using delegation to replace the delegate with another object at runtime? Recently we described the advantages of delegation at the lecture, but no actual example was given to an above benefit.
Thanks in advance!
Let's say we have a C# delegation like this:
delegate int Calculate(int x, int y);
The benefit here is that, when a method foo expects a Calculate delegation in its parameter, like this:
void foo(Calculate calculate)
{
var result = calculate(1, 2);
// ...
}
We can easily pass any method that matches the signature of the delegation to foo. For example, if we already have a method sum of class Math, we can simply call foo like this:
foo(mathObject.sum);
Without delegation, like in Java, we have to make Calculate be an interface, and have to make the Math class implements Calculate. If we are not allowed to modify source code of Math class, we have to write an adapter (Adapter design pattern). That's a lot of extra work.
I'm a beginner of Kotlin, there are many omitted code with Kotlin. It make me crash when I read some sample code.
Such as var map=HashMap()
I can't judge what HashMap() is function or class. I have to judge it by Hint of Android Studio. Do you have a simple way?
If I use java, it will be different code style.
Function: Map map=myFunction()
Class: Class myClass=new Class()
First, if you follow Java naming conversion, class is PascalCase and function is camelCase.
Second, it does not matter. Creating a new object is just a constructor returning an object. It does not different from a a function return an object.
I can't judge what HashMap() is function or class
Don't think of this as class or function. HashMap() is a constructor which is really a method (function) that returns an instance of an object. So there is really no need of the new keyword here, and it make for clean code.
You can identify if it's a function or a constructor based on the Name itself (the case of the name).
So I'm new to Scala (and have almost zero java experience). I thought I understood OOP, in abstract, but disregard that. My question -- in a similar vein to "method name qualification when using a companion object" -- is about when a Scala pro would think to implement a class - companion object pattern?
From the question referenced above, it's not clear that companion objects were intended to store methods for the class's "internal use" (e.g. the poster wanted to use ^, defined in the object, inside /, defined in the class). So, I don't want to think of companion objects as "containers" for methods the companion class can use, because that's clearly not true...
I'm sorry if this is a vague question: I just want to know the correct way to use these guys.
Companion objects are useful for what you would use static methods for in Java...
One very common use is to define an apply() method in the companion object, which gives users the ability to use MyObject(arg, arg) as shorthand for new MyObject(arg, arg).
Companion objects are also a good place to put things like implicit defs.
I recently have been using companion objects in my akka apps as places to put message case classes which are specific to a supervisor actor and its children, but that I don't necessarily want code outside that subsystem to use directly.
Here's a simple example:
class Complex(real:Double, imag:Double) {
def +(that:Complex):Complex = Complex(this.real + that.real, this.imag + that.imag)
// other useful methods
}
// the companion object
object Complex {
def apply(real:Double, imag:Double) = new Complex(real, imag)
val i = Complex(0, 1)
implicit def fromInt(i:Int) = Complex(i, 0)
}
The normal OOP way to instantiate a new Complex object would be new Complex(x, i). In my companion object, I defined the function apply, to give us a syntactic sugar that allows us to write Complex(x, i). apply is a special function name which is invoked whenever you call an object directly as if it were a function (i.e., Complex()).
I also have a value called i which evaluates to Complex(0, 1), which gives me a shorthand for using the common complex number i.
This could be accomplished in Java using a static method like:
public static Complex i() {
return new Complex(0, 1);
}
The companion object essentially gives you a namespace attached to your class name which is not specific to a particular instance of your class.
RealBasic's Introspection is kinda of different than what I expected.
My intention is:
Create a MainObject from which other objects will inherit two, three methods, to simplify.
Method 1-> Returns to the child class itself all of its properties, types and values.
Method 2-> Would call Method1 and with the information, save the child Object.
So, for method 1 I thought about writing a generalised introspection which for each child class would easily return what I need for Method 2 to do its work.
Why do I want this? So I can have tens of objects knowing how to save, draw themselves without worrying too much about a modification here or there on the properties etc...
But using what RealBasic tutorials and reference offers doesn't work, since it requires me to have it happening outside the object etc... i.e.: I can easily, inside ObjectA, get ObjectB's properties, methods etc, but I want to get inside ObjectA, A's properties, not B's
Thanks in advance...
I've found out how... Very simple, create the MainClass and inside of it a simple method WhoAmI which could return an array, dictionary etc...
Dim thisClassTypeInfo As Introspection.TypeInfo = Introspection.GetType(Self)
Dim thisClassProperties() As Introspection.PropertyInfo = thisClassTypeInfo.GetProperties
Dim thisClassMethods() As Introspection.MethodInfo = thisClassTypeInfo.GetMethods
For Each myProperty As Introspection.PropertyInfo In thisClassProperties
// Then here use myProperty.Name, myProperty.Value(Self).StringValue
// or myProperty.Value(Self).anyotheroption and create a dictionary
// or array with the results and return it.
Next