I have an inherited class which i would like to point to from the base class. Example below
class Base
{
inherited* test;
};
class inherited: Base
{
};
the purpose of this is so that the base class (a character) contains a linked list of the inherited class (items)
ps apologies for any mistakes, i'm new to this site
It might be possible to trick the compiler into accomplishing this, but it's most certainly bad OOP design. If all you want to do is be able to store an instance of the inherited class but can treat it like the base class, then you can simply make inherited* test a base* test and it will accept pointers to either inherited or base (or any other subclass of base).
If you actually want base to treat that instance as inherited, you need to rethink your class hierarchy because you don't actually have an inheritance tree here.
Related
We are having a UML course. The teacher said:
Every class should be declared as abstract if it serves as base class for
its derived classes.
In the following figure suppose that we want to derive class german shepherd and class labrador from class chien (Dog woof woof). Is it an obligation for class chien to become an abstract class or not?
Not necessarily.
That statement isn't necessarily true. A more correct statement would be:
Every class should be declared as abstract if it cannot be instantiated without referring to a concrete derived class.
In your example, it makes sense that Dog and Animal would be abstract, because you have more specific classes that likely fill out details that the base classes do not.
However, it is certainly possible to have a class which is concrete and can be instantiated, (and therefore not abstract), but still serve as the base for another class.
It should be abstract if it's a generalization and cannot exist on it's own.
Look at this situation:
In the image above Relation is abstract. It can't exist by it's own. Customer and Employee are normal classes who extend Relation. But Trainee is a Employee.
You could create a Employee, but also a trainee which is a Employee as well.
I missed a few CS classes, namely the ones going over topics such as polymorphism, inheritence, and abstract classes. I'm not asking you to do my homework but I have no idea where to even start to get further guidance, so giving me a skeleton or something would help me greatly, I'm so confused.
So the problem is to create an employee abstract class with two subclasses, permanentEmployee and TempEmployee.I must store information such as name,department,and salary in these subclasses and then order them according to how the user wants them ordered. I know I start out like this
public abstract class Employee
{
}
public class TempEmployee extends Employee
{
\\variables such as name, salary, etc, here?
}
public class PermEmployee extends Employee
{
\\here too?
}
but I have no idea how to store variables in there much less access them later for ordering and displaying,. Please guidance.
If all you're looking for is an example of class-level data members in Java, this should help:
public class SomeClass {
private int someInt;
public int getSomeInt() {
return this.someInt;
}
public void setSomeInt(int someInt) {
this.someInt = someInt;
}
}
Regarding polymorphism, be aware that methods are polymorphic, but values are not. As you place values and methods (getters and setters) in your base class and derived classes, I encourage you to experiment with these concepts thoroughly. Try moving the entire value/getter/setter to the base class, try moving just the value but not the getter/setter, try putting the value in both and the getter/setter in both, etc. See how it behaves.
Make sure that any value/method/etc. that you put in your base class is applicable to all derived classes. If there's ever an exception to that rule, then you would need to move that member out of the base class and into only derived classes where it applies. Note that you can have a complex hierarchy of base classes to accommodate this if needed.
When it comes time to access these members for sorting/display/etc., consuming code would use the getters/setters. For example:
SomeClass myInstance = new SomeClass();
myInstance.setSomeInt(2);
System.out.println(myInstance.getSomeInt());
I am not sure which language you working with, but as it has "extends" I am sure you are not working with c# or CSharp, it can be Java. So I would recommend you to go for TutorialsPoint. This particular article has abstraction described here.
Just to make it easy for you, in Interface and abstraction we always create a structure or the base, it has all the common things defined or declared (Obviously interface has only methods and no variables can be declared inside it).
So as said, in above example, EmployeeId, EmployeeName, EmployeeAddress ...etc should be defined in the base class that is Abstract Base class Employee, But in TempEmployee you can have a criteria such as EmpTermPeriod, EmpContractRenewalDate, EmpExternalPayrollCompanyName (Have made names long and self descriptive) and PermEmployee to have fields like EmpJoiningDate, EmpConfirmationDate, EmpGraduityDate...etc.
I hope it helps.
The documentation says
Abstract classes are essential to support Object Orientation without the typical spamming of the database with always empty auto-created clusters.
But it also says
A class that can't have instances
However, I would like to embed a list class B in class A, not have class A inherit from the abstract class B. Is this allowed?
Example:
enter code here
propVal {
locType : ""
eleName : ""
...
values :[valueStamp]
}
valueStamp {
value : any,
stamp : actionStamp
}
actionStamp{
// various attributes that say who, when, where change was made
}
Is used in many classes keeping track of changes to various fields.
They will never be used stand alone, but can't inherit because they can be used more than once in a class
Sample parent class
classA{
helperAId:"",
helperAProps : embeddedList of PropVals,
helperBId : "",
helperBProps : embeddedList of PropVals
}
Important: The class hierarchy supported by OrientDB is similar to OO principles as implemented by popular languages like Java. However, it is not the same, so there are important differences!
Yes you can embed a (list of) class(es) of type B in a class type A. This is perfectly valid and a much used construct. This is done using the EMBEDDED type.
OrientDB does not support the concept of interfaces or mixin's, just classes and abstract classes. So a class can only inherent (extend) a single parent class. In your use case I would create an abstract ActionStamp class (or whatever you name it) and let your other classes extend it.The B and A classes can both extend this ActionStamp class
So, using your example:
CREATE ABSTRACT CLASS propVal
...
CREATE CLASS A
CREATE PROPERTY A.helperAProps EMBEDDEDLIST propVal
...
Among my two processes' functionality, there is a common function to merge files. I need not going to insist any of the processes to have some methods as interface does. And, also the two processes are independent. So, is it fine I just go with an Abstract class and have the implementation in that abstract class itself? Also I do not need any abstract method.
Inheritance is used when there is IS-A relation between subclass and the base class. I don't think it is the case here. You didn't specify the language, but from your profile I guess you use Java. So if you use an Abstract Class you won't be able to inherit from other, more appropriate class in the future.
Instead of inheritance you can use composition. Which means that you create a regular file merging class which has this method to merge files. And in classes where you want to have this functionality you just instantiate this new file merging class. It lets you inherit from other class in the future.
If you want to inform the world that those classes can merge files (to use polymorphism), and you use Java 8 you can create default method inside an interface and implement this interface without override this default method. But I think composition will be better in this case.
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.