What is the difference between a Plain Class Vs Abstract Class Vs Interfaces. Kindly, explain the same using snippets and demo.
Class:
It is a class without any abstract members. You can instantiate normal Class where as you cant instantiate Interface and Abstract class; you can just inherit from Abstract and Interface. Inherit from it (unless the class is sealed), use its methods, override those methods, etc.
Abstract Class:
May/mayn't contain Implementations; At least one member will not be implemented. A Class may inherit from a single Base class; multiple inheritance not allowed. Members have access modifiers May contain fields, properties, constructors, destructors, methods, events and indexers.
Interface:
Does not contain Implementations Interface can inherit from a number of interfaces(Multiple inheritance supported) Members are automatically public May contain properties, methods, events and indexers
Related
What is the difference between:
class A {}
class B with A{}
and
mixin A{}
class B with A{}
?
In Dart, a class can only extend one other class. But it can implement or mixin as many as you want.
The thing is, when you extend a class, you inherit all its attributes, methods and it's constructors. When you implement a class, if you are adding only methods/attributes that you don't already have, you can simply continue your code. If you are implementing an abstract method, you'll need to actually implement it. Now, mixins are like extended classes, the classes that mix them, are their child as well as with extend and implements, but it has no constructor.
The actual idea for mixins is that you can add functionalities to any class, and they don't have to extend another class. That's why they usually do simple stuff only.
how can a class or interface can extend more than one class in java Please help..
Steps:::javap java.time.chrono.ChronoLocalDateTime in cmd prompt
Compiled from "ChronoLocalDateTime.java"
public interface java.time.chrono.ChronoLocalDateTime<D extends java.time.chrono.ChronoLocalDate> ex
tends java.time.temporal.Temporal, java.time.temporal.TemporalAdjuster,
Excepting Object, which has no superclass, every class has one and only one direct superclass (single inheritance). In the absence of any other explicit superclass, every class is implicitly a subclass of Object.
if you need multiherence you need implements interfaces
look this
https://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
I'm using the Mixin pattern as illustrated below. Why does Typescript require you to provide stand-in properties for private properties of the mixin class in the target class (A)? It perfectly makes sense for the public properties, but for private properties it unnecessarily crufts up the target class with details of the internal implementation of the mixin class by requiring them to be stubbed-out in the target class. Seems like the Typescript transpiler should be able to not require this.
class Mixin {
private foo:string;
}
class A implements Mixin {
// stand-in properties, typescript requires even
// private properties to be stubbed-out
foo:string;
}
Private members contribute to the structure of a type in TypeScript, so if you don't implement them you are not compatible with the type. This actually makes it impossible to match a type structurally in TypeScript if it has a private member, because you are either:
a. Failing to provide the type
or
b. Providing a separate implementation of the private member
So you can only extend a type with a private member, not implement it.
With this in mind, you are better off not using private members with mixins. Provide the ghost-members in the implementation class and keep your fingers crossed that if mixins gain some traction the ghosting will become unnecessary (see TypeScript mixins part one).
In C++ I can make interface and class declarations. However, in contrast to C# the interface here is very likely to be a class so why is it there ?
interface Interface {
};
And
class Class {
};
As has been mentioned in comments, standard C++ does not support an "interface" construct directly. This is an extension from some vendors.
Other languages do (e.g Java).
The equivalent in standard C++ is an abstract base class, which does not have data members.
class SomeInterface
{
public:
virtual ~SomeInterface() = 0;
virtual void SomeAction(int flag) = 0;
};
Inheriting from such a class forces the derived class to override/implement all virtual functions, otherwise they cannot be instantiated.
Generally speaking, an abstract base class without data members can often get away without having non-trivial constructors (since the class has no members to initialise).
Unlike other languages that do support an interface construct, the abstract base class permits;
Having data members in the base class. (In which case constructors, destructors, assignment operators, etc may need to be defined to manage those members)
Having some members pure virtual and some not
Providing implementations of pure virtual methods (which must be explicitly overridden by derived class, but the base class version can be called)
Whenever I create an abstract class I tend to create an interface to go along with it and have other code refer to the interface and not the abstract class. Usually when I don't create an interface to start with I regret it (such as having to override all implimented methods to stub the class for unit testing or later down the line new classes don't need any of the implimentation and override everything also finding themselves unable to extend any other class).
At first I tried to distinguish when to use an interface and when to use an abstract class by considering is-a vs able-to but I still would end up suffering later down the line for not making an interface to start with.
So the question is when is it a good idea to only have an abstract class and no interface at all?
When you wish to "give" some base class functionality to derived classes but when this functionality is not sufficient to instantiate a usable class, then go for abstract classes.
When you wish that some classes completely implement a set of methods (a public contract), then it is a convenient to define such contract with interfaces and enforce them onto classes by making them inherit this interface.
In short:
With abstract classes you give some common base functionality to derived classes. No further actions are necessary unless abstract class has some stubs (which have to be implemented down there).
With interfaces you require derived classes to implement a set of functions and you do not pass along any implementation.
So the question is when is it a good idea to only have an abstract class and no interface at all?
When you do not wish to enforce any public contract (a set of methods/properties defined by an interface).
Also when you do not plan to use certain coding techniques like casting object to an interface type (run-time polymorphism) or limit allowed input (some method argument will only accept object of types which implement certain interfaces).
Well, the main case it is useful to have only an abstract class without any interface is to mark a certain type. It is useful to be able to check if an object "is-a" something. These interface "mark" an objet to be of a certain type. Depending on the language you use, different design patterns apply ...
These sort of abstract classes exist in java. You can also use them in C++ with RTTI.
my2c