What does doing the following mean, I've been seeing it around online a lot and don't understand why the word object is written
class Solution(object):
Thanks in advance.
It's called 'Inheritance'.
You can read more in section 9.5 here.
https://docs.python.org/3/tutorial/classes.html
class likes a blueprint. as an example you can consider a registration form, this form is a class and if you fill up a copy of this form it will be an object.in a class we have some variables are called attribute or field and we got some functions that each of them is called method. if you allocate some space of your memory to an unit which has value for all attributes of your class, this is your object.
Related
I'm exploring if Byte Buddy is the right tool for me to use. I was looking at this answer which talks about how with Byte Buddy, one can take a class Foo loaded with class loader A, rename it to Bar and redefine it on another class loader B. That's incredible.
My question is:
Is it possible to have an object which was created from Foo on class loader A and convert to Bar's object which is coming from class loader B? The solution which I have in mind right now is to basically serialize the object from Foo and then edit the serialized bytes to rename the name of the class. It would be nice if I can do it safely with Byte Buddy. Another solution would be to use Transloader.
Is java-agent or any special instrumentation required for doing all the things that was described in the above SO answer
Thank you so much.
You can always load a class in another class loader without using a Java agent. As for translating the class, replacing the symbol of one class name to anther should not be a problem but you need to watch out for serial version UIDs where there name of the class might be a part of. Byte Buddy is a code generation library and does not add any extra help for such operations.
I work with a codebase where there are many classes with thousands of lines of code. I've noticed inconsistencies in style concerning prepending class names when using their methods and I'm trying to figure out the previous developer's reasoning. If we
import GeneralCode
in Class A, is it bad practice to write
GeneralCode.DoSomething()
in Class A since we already imported it (instead of simply using DoSomething())? I would think so, but I suppose it's also nice to know which methods come from which classes at a glance, since Class A imports many classes and uses methods from several of them.
EDIT: This is for VB.NET, not Java (sorry for the wrong tag, rough morning). I am new to VB.NET but GeneralCode and DoSomething() are not declared as static, neither is the import in Class A.
Might be something to do with VB.NET, but DoSomething() can indeed be used with or without prepending GeneralCode.
A method need to be prefixed with
The class name if it's a static method.
The name of the instance when it's not a static method.
Unless you are calling a method from your own class.
I'm currently trying to learn how to use GObject and there's a point I absolutely don't understand: What's the difference between the class and the instance structure (like "MamanBarClass" and "MamanBar") resp. how do I use them? At the moment I'd put all my object attributes into a private structure (like "MamanBarPrivate"), register it with "g_type_class_add_private" and define properties/getters/setters to access them. But when I leave the class structure empty I get the following error at "g_type_register_static_simple":
specified class size for type `MamanBar' is smaller than `GTypeClass' size
And why are all object methods defined in the class structure (like "GtKWidgetClass")? Probably I'm just screwing up everything, but I only worked with Delphi for OOP yet (I know, nothing to be proud about :D)
Regards
I'm currently trying to learn how to use GObject and there's a point I absolutely don't understand: What's the difference between the class and the instance structure (like "MamanBarClass" and "MamanBar") resp. how do I use them?
The class structure is only created once, and is not instance-specific. It's where you put things which are not instance-specific, such as pointers for virtual methods (which is the most common use for the class struct).
At the moment I'd put all my object attributes into a private structure (like "MamanBarPrivate"), register it with "g_type_class_add_private" and define properties/getters/setters to access them.
Good. That's the right thing to do.
But when I leave the class structure empty I get the following error at "g_type_register_static_simple":
You should never leave the class structure empty. It should always contain the class structure for the type you're inheriting from. For example, if you're trying to create a GObject, the class structure should look like this (at a minimum):
struct _MamanBarClass {
GObjectClass parent_class;
};
Even if you're not inheriting from GObject, you still need the base class for GType:
struct _FooClass {
GTypeClass parent_class;
};
This is how simple inheritance is done in C.
And why are all object methods defined in the class structure (like "GtKWidgetClass")? Probably I'm just screwing up everything, but I only worked with Delphi for OOP yet (I know, nothing to be proud about :D)
Those are virtual public methods. As for why they're defined in the class structure instead of the instance structure, it's because the implementations are the same for every instance.
I've been battling with AS3 for a little while now, and I'm working on a simple application using only actionscript and the FlashDevelop/flex-compiler combo. I've hit a bit of a wall in my fledgling OOP understanding, and I'm wondering whether someone might be able to point me in the right direction. I have genuinely read several books, and spent many hours reading online tutorials etc, but something's just not clicking!
What's baffling me is this: When something is declared 'public', according to what I read, it is therefore available anywhere in the application (and should therfore be used with care!) However, when I try to use public properties and methods in my program, they most definitely are not available anywhere other than from the class/object that instantiated them.
This leads me to conclude that even if objects (of different class) are instantiated from the same (say 'main') class, they are not able to communicate with each other at all, even through public members.
If so, then fair enough, but I've honestly not seen this explained properly anywhere. More to the point, how do different objects communicate with other then? and what does Public actually mean then, if it only works through a direct composition hierarchy? If one has to write applications based only on communication from composer class to it's own objects (and presumably use events for, er, everything else?) - isn't this incredibly restrictive?
I'm sure this is basic OOP stuff, so my apologies in advance!
Any quick tips or links would be massively appreciated.
There are different topics you are covering in your question. Let me clarify:
What does the modifier public mean?
How can instances of the same class communicate to each other?
--
1.
In OOP you organize your code with objects. An object needs to be instantiated to provide its functionality. The place where you instantiate the object can be considered as the "context". In Flash the context might be the first frame, in a pure AS3 movie, it might be the main class, in Flex it could be the main mxml file. In fact, the context is always an object, too. Class modifier of your object public class MyClass tells your context whether it is allowed to instantiate the object or not. If set to internal, the context must live in the same directory as the class of the object. Otherwise it is not allowed to create a new object of the class. Private or protected are not valid class modifiers. Public class ... means that any context may create an object of that class. Next: Not only instantiation is controlled by these modifiers but also the visibility of a type. If set to internal, you cannot use an expression like var obj : InternalType in a context that does not live in the same directory as Internal type.
What about methods and properties? Even if your context is allowed to access a type, certain properties and methods might be restricted internal/protected/private var/method and you perhaps are not able to invoke them.
Why we're having such restrictions? Answer is simple: Differnent developers may develop different parts of the same software. These parts should communicate only over defined interfaces. These interfaces should be as small as possible. The developer therefore declares as much code as possible to be hidden from outside and only the necessary types and properties publicly available.
Don't mix up with modifiers and global properties. The modifier only tells you if a context is allowed to see a type or method. The global variable is available throughout the code. So even if a class is declared to be public, instances of that class do not know each other by default. You can let them know by:
storing the instances in global variables
providing setter such as set obj1(obj1 : OBJ1) : void where each object needs to store the reference in an instance variable
passing the object as method arguments: doSomething(obj1 : OBJ1)
Hope this helps you to more understand OOP. I am happy to answer your follow up questions.
Jens
#Jens answer (disclaimer: I skimmed) appears to be completely correct.
However, I'm not sure it answers your question very directly, so I'll add a bit here.
A public property is a property of that class instance that is available for other objects to use(function: call, variable: access, etc). However, to use them you must have a reference (like a very basic pointer, if that helps?) to that object instance. The object that instantiates (creates, new ...) that object can take that reference by assigning it to a variable of that class type.
// Reference is now stored in 's'
public ExampleClass s = new ExampleClass();
If you'd like to, you do have the option of making a static property, which is available just by knowing the class name. That property will be shared by all instances of that class, and any external class can refer to it (assuming it's public static) by referring to the class name.
A public property is referred to by the reference you stored.
//public property access
s.foo
s.bar(var)
A static property is referred to by the class name.
//static property access
ExampleClass.foo
ExampleClass.bar(var)
Once you've created the instance, and stored the reference, to an object, you can pass it around as you'd like. The below object of type OtherExampleClass would receive the reference to 's' in its constructor, and would have to store it in a local variable of its own to keep the reference.
public OtherExampleClass s2 = new OtherExampleClass(s);
I want to create an object from a class that I have created. What I have been trying is to create the object (which can be testingclass) from a method of another class, which I will call classexample, but it says that testingclass is undeclared, which I assumed meant that it was out of the scope of the method, and the method couldn't access it. My program doesn't have a main function like in c or anything so I don't really understand where to put code that involves different objects if it can't go in methods.
Do you have the header file of the testingclass and did you import it to the file that create that object? That's all I can guess for your problems with very little information for very strange problem.