I have three classes. Class1, Class2 and Class3. I have circular dependency(class1 to class2, class2 to class3,class3 to class1). In this case how resources will be free by dispose method or finalize()?
When you implement IDisposable on an object you also make a decision of ownership. If Class1 has a reference to Class2 you have to decide if Class1 owns Class2 or if it just stores a reference. If Class1 owns Class2 and Class2 is IDisposable then Class1 should also implement IDisposable and Class1 should call Dispose on the Class2 reference in the Dispose method, but only when called explicitely - not when finalized.
Because IDisposable also defines an ownership hierarchy you cannot have circular dependencies when disposing. Of course Class1 can own Class2 that owns Class3 and Class3 can have a reference to Class1 but because Class3 doesn't own Class1 it should not call Dispose on the reference when disposed.
During finalization a class that implements IDisposable should only release unmanaged resources and not call Dispose on classes that it owns because these instances may already have been finalized by the garbage collector.
Related
Which class is Abstract class in Objective-C, I have read some doc where NSObject is Abstract class, but we can create instance of NSObject, then how it is follow the abstract class rule.
NSObject *obj = [[NSObject alloc] init];
NSLog(#"description = %#",[obj description]);
NSLog(#"class name = %#",[obj class]);
Please advice.
And also I heard another one Abstract Class in Objective-C, what is the name of the class?
Objective-C has no compile time restraint against instantiating abstract classes. See Creating an abstract class in Objective-C
In Objective-C there is no language level concept of an abstract class. You have to read the documentation for a class to find out if it should be treated as an abstract class. There are a few such classes in Cocoa, e.g. NSObject, NSProxy and NSOperation. It's more common for behaviour to be defined in protocols rather than in abstract classes.
The Cocoa framework contains to root classes (i.e. class which do not have superclasses). NSObject is one root class and NSProxy is the other. NSProxy does not implement an init method which means an exception is raised when you attempt to create an instance.
I know usually, when you want to call a method on another object, you do:
NewObject *object = [NewObject alloc]init];
[object callMethod];
But I created a class that isn't an object itself meaning it doesn't have properties or memory management. It has a couple methods that calculate some stuff.
From any other class, all I have to do is import the header for this class and do:
#import "MyClass.h"
[MyClass callMethod];
Why in this case do I not have to alloc init? It works just fine.
It sounds like you are trying to call a class method. These are methods which have been defined as:
+(void) myStaticMethod;
instead of
-(void) myMethod;
The plus sign indicates that the method does not use any fields, and thereby does not need to instantiate the object.
In your example, "object" is an instance of a class "NewObject" which has been allocated memory and initialized. Where-as your example, "MyClass" is only a class which because it has static members declared as above, does not need to be instantiated.
Class methods provide a nice way to combine a bunch of related functions into one place, rather than having them spread out in the regular namespace, as would usually be done in straight C. You can also have both class methods and instance methods in the same class, using the class ones when needed, and instantiating the class to use the instance ones when needed.
EDIT: Changed terminology to refer to class methods instead of static methods.
because you are calling a class method. You only need to alloc init objects. Classes only need to be included but not alloc inited. So you don't need to init an NSString class, say.
Edit:
Let's just have some nonsense examples:
+ (void)classMethod {
NSLog("Hi!");
}
[SomeClass classMethod]; // prints Hi!
- (void)instanceMethod { // (say it's an instance method of NSString)
NSLog(self);
}
[#"someNSString" instanceMethod]; // prints someNSString. But you need to have a string first, otherwise you cannot use this method.
There is a difference between "instance" methods (normal ones), that have to be called on an object and have access to self, and "class" methods (called static, in many programming languages), that are invoked on the class and thus do not have a self.
Class methods are similar to C++ static methods, in that they can be invoked without creating a concrete instance of the class. The usefulness of this is you can call a class's specialized factory methods to create a new instance; or, you can define a utility library under the scope of a class that may or may not provide concrete instances depending on the task.
Look at NSDate and NSNumber are good examples of this in the Foundation framework.
I created a Class A in which all the methods are class methods (+). Another Class B is a singleton.
I want to know if I can check if Class A [A someoperation] Is like class B in that only one instance of A exists and I do not need to instantiate it.
How can I accomplish this?
When you call a class method, the class is not necessarily instantiated, unless the class method actually creates a class.
Also - class methods do not make a class a Singleton. It just means that the method is called on the class instead of an objet of the class.
I have a custom deferred binder (rebind implementation) that instantiates objects. I would like to have some dependencies (#Inject annotated setter methods) within the instance returned by GWT.create() fulfilled by GIN. Is this possible?
So, given code such as:
Foo foo = GWT.create(Foo.class);
if foo's final implementation has:
#Inject
public void setBar(Bar bar) {
...
}
how do I get bar injected into the returned foo instance automatically by GIN?
Your Ginjector can have methods added to it for the purpose of injecting objects created in some other way. These must take one argument, and should specify the most specific type possible. For example, if MyViewImpl extends BaseView, and both types have dependencies to inject, but you declare
void injectBaseView(BaseView view);
in your ginjector, only the fields/setters declared on BaseView will be dealt with.
EDIT: Also, if no binding is declared, GWT.create will be used to create an instance, so you can have your cake and eat it to. One exception to that as far as I can recall, is when you want to GWT.create one type, but return another (see RPC interfaces for an example).
I have a clue about Object Oriented Programming:
I need to have a parent class HandlerException which needs to define the sign of three methods (MethodA, MethodB, MethodC).
Then, I have a child class BusinessHandler which inherits from HandlerException and defines ONLY the MethodA of its parent class.
Then, I have a child class DataHandler which inherits from HandlerException and defines ONLY MethodC of its parent class.
Then, I have a class named CustomerDAO which inherits from DataHandler and consumes the MethodC written on its parent class. (consumes it like: DataHandler.MethodC).
As you can see, its a typical object oriented programming problem; I need to have some static methods (MethodC) to access it directly without any instance of the class. The parent class HandlerException could be abstract? and its 3 methods (A, B and C) could be ???? (that's my question, how is the RIGHT way to write this parent class: abstract with abstract members, or virtual, or maybe an interface?)
I hope you got the idea of my question and that I made myself clear. Thanks in advance.
I forgot: I'm using C#, and to mention: MethodB would be implemented on the next release of the app.
Depends on the language you are using, but it sounds like the HandlerException class would be abstract and all three methods would be virtual.
If the HandlerException class has absolutely no implementation whatsoever (only defines those three methods) then it would probably make sense to make it an interface rather than an abstract class.
Also, where is MethodB implemented? If it isn't implemented by any of those classes, then all the classes would need to be abstract.