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.
Related
I have two classes: ChildOne and ChildTwo extended from ParentClass. ChildTwo has a custom field over the inherited ones.
In some parts of the app, most of the time this ParentClass is used to display data to UI and some widgets need to know if the instance is ChildTwo to display the custom field.
However in another part of the app, I have to enhance the ParentClass, so I created another class EnhancedParentClass extends ParentClass.
This class use used in most of the widgets, but again there are some widgets that need to know the difference between the EnhancedParentClass and let's say an extended class ChildTwoEnhancedClass.
What’s the best way of solving this?
class ChildTwoEnhancedClass extends EnhancedParentClass implements ChildTwo
class ChildTwoEnhancedClass extends ChildTwo implements EnhancedParentClass
Is there a way to do this, without the need to extend the main classes “in paralel” with the “enhanced” one? Or is it something completely wrong with this implementation?
I looked over mixins, but I don’t think they fit this case, as far as I’ve seen mixins are used to share logic(mimic multiple inheritance), not necessarily share class members.
These classes are used as data immutable models.
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 would like to create a subclass of akka.agent.Agent. I have tried the following...
import akka.agent.Agent
import markets.tickers.Tick
class TickerAgent(val initialValue: Tick) extends Agent[Tick] {
???
}
...at which point I am prompted to implement the remaining methods of the abstract Agent class. However, I want to keep the default implementations for these methods. It seem from the source that the default implementations are defined in a final, private SecretAgent class inside the Agent companion object.
Is there anyway for me to somehow import or otherwise access the default Agent when implementing a subclass of Agent?
According to my knowledge, there is no other way except implementing the abstract methods defined Agent[T] class. You can call the default methods inside your methods implementation.
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