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
Related
I have this question for a job interview, and i want to know why the stateful and staless widgets, use extends and why not use implements in Flutter/Dart?
Extends
extends is usually the go-to when you want to make a more specific version of a class.
When you extend a class, you inherit all properties, methods, etc.
If you want to override a method, you prefix the method with #override.
Implements
implements is when you want to make a whole new version of a class but you want to inherit the class type.
When you create a new implementation of a class, you are responsible for supplying everything necessary to make that class function.
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
I'm trying to implement a custom preference dialog using the FilteredPreferenceDialog class.
The problem that this is an abstract class, but I dont really understand why. It has no abstract methods. I created my own class which extends FilteredPreferenceDialog but then I get the discouraged access warnings. There is another class called WorkbenchPreferenceDialog which also extends FilteredPreferenceDialog, and its also abstract.
Is there a class which is a public not abstract class I can create which has the filtering implementation? The PreferenceDialog class works fine except it doesnt have the filtering mechanism.
what is the difference between doing a class as subclass by inheritance and composition
Composition : the new class has the original class as an instance variable. The interface of the new class starts from the scratch. Only the properties and methods that the new class defines are available to the users of the class. The new class internally uses the old class object.
Subclass : the new class has all the properties and methods it's superclass defines. Any users can use the properties and methods. If the new class does not override them, the superclass implementation is automatically called. The subclass may add new properties or methods.
Usually subclassing is more helpful, but some cases composition can be helpful ( for example when working with class clusters).
http://www.artima.com/designtechniques/compoinh.html
http://www.mapleshirefarm.com/eric/CompositionVsInheritance.html
http://www.apl.jhu.edu/Notes/LMBrown/resource/Composition.pdf
and concisely...
http://www.codeproject.com/Articles/80045/Composition-VS-Inheritance.aspx
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.