Why Constructors are not inherited?

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I have been learning constructors in Inheritance using Eclipse Juno.

When I press ctrl+O twice in the childClass, It shows inherited members. But I happen to see even the Constructor of super class in the inherited members

But it is said that constructors are not inherited...

Can someone please explain this behaviour?

Unlike fields, methods, and nested classes ,Constructors are not class members.

From docs of Inheritance

A subclass inherits all the members (fields, methods, and nested classes) from its superclass. Constructors are not members, so they are not inherited by subclasses, but the constructor of the superclass can be invoked from the subclass.

But why constructor removed from class member ??

Why are constructors not inherited?, is called implicitly when the new keyword is used so it can't lack a body. Constructors are different from other class methods in that they create new objects, whereas other methods are invoked by existing objects. This is one reason constructors aren’t inherited.

Only members are inherited, and a constructor is not considered a member.

To understand why constructors are not inherited, consider that inheritance in OOP is part of the mechanism that allows an object to be treated as another, more general object. This requires that all data members and all methods are inherited.

What inheritance is not intended to do, is allow one object to be instantiated in the same manner as another, more general object.

This is because a constructor must initialize an object to a valid state and what's enough information to initialize valid state for a superclass object might not be enough information to initialize valid state for the subclass object!

To work around this, if constructors were inherited, when you extended a class from a library you'd have to manually opt out of the constructors you don't want inherited. This is cumbersome and error prone, as when a new version of that library comes out with more constructors in that base class, your own class is now subject to invalid initializations (through the leaked constructors), unless you release an update too. Or it could be that adding a constructor in your own superclass will "break" your own subclasses and you'd have to go to each subclass and opt out of the new ones. In other words, the validity of your code would be more tightly coupled to the base you've used.

On the other hand, "opting in", by defining your own constructors explicitly and chaining them with those of the base class makes more sense practically and is safer for the validity of your component. This opting in is done by chaining, the process of invoking a base class constructor at the beginning of another constructor.

Now Eclipse (which I don't use, so I'm basing this on what you're describing in your question) may probably be listing the constructors available for use in chaining because looking for them is a very common scenario (unless you're invoking a very simple or parameterless constructor). In other words, the constructors are listed in the inherited members for convenience but, as we've said, strictly speaking, they are not inherited.

Copy constructor is not inherited, Why Constructors are not inherited in Java? Constructor is a block of code that allows you to create an object of class and has same name as class with no explicit  I.e. why not be able to specify a constructor as virtual – Noon Silk May 3 '10 at 7:31 The designers of C# (and Java), could easily have defined a rule that says that the constructor in Object is not inherited, but still invoked implicitly.

Constructors are chained: each constructor you write must eventually invoke one of the superclass constructors. Example:

public class MyException extends RuntimeException {
    public MyException(String message) {
        super(message);   // invokes RuntimeException(String) constructor
    }
}

A super(...) or this(...) constructor invocation, if any, must appear as the first statement in your constructor. If neither of those is specified, super() is implicitly assumed, which will chain up to the superclass's default constructor. (And if the superclass has no default constructor, then the compilation will fail.)

Why Constructors are not inherited in Java?, Subclass inherits all the data members,member functions and nested classes from its super class. Constructors are not member, so they are not inherited by sub  First of all, constructors are not members of classes, and only memebers are inherited. Second, we can imagine cases for which we don't want subclasses to have the same constructors than the parent class. Imagine an abstract class Vehicle with a constructor Vehicle(int wheels), and a subclass Bicycle.

Constructors are not members, so they are not inherited by subclasses, but the constructor of the superclass can be invoked from the subclass.

Source: http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html

Eclipse method help using Ctrl+O shows what all methods that you can call from the current class. Hence parent constructors are also displayed in that as you can call it using super.

Why constructors cannot be final, static and abstract?, There can't be any proper inheritance of constructors in C++, because the constructor of a derived class needs to perform additional actions  Constructors are not inherited. When a subclass is instantiated, the superclass default constructor is executed first.

Why are constructors not inherited?, Hi members, #GainJavaKnowledge Here i will explain you Why constructors are not inherited Duration: 3:55 Posted: Jul 30, 2018 A constructor is never inherited to an another class so it doesn't need to be marked final. Also it cannot be marked final. apply a final keyword to a method means you cannot override that method. but by default in java no constructor can be overridden. so there is no need to use final keyword with a constructor .

Why Constructor Are Not Inherited In Java, Constructors are Not Inherited In Java A Job Portal http://www.InterviewDot.com http://www Duration: 1:55 Posted: Mar 24, 2014 This is a situation which only matters if there is a default constructor. The constructor of a base class (or base classes) can also be called by a derived class. Constructor functions are not inherited and their addresses cannot be referenced. When memory allocation is required, the new and delete operators are called implicitly.

Constructors are Not Inherited In Java, Constructors are not members, so they are not inherited by subclasses, but the constructor of the superclass can be invoked from the subclass. The Java Platform  I was wondering why in java constructors are not inherited? You know when you have a class like this: public class Super { public Super(ServiceA serviceA, ServiceB serviceB, ServiceC serviceC){ this.serviceA = serviceA; //etc } } Later when you inherit from Super, java will complain that there is no default constructor defined.

Comments
  • Check the link: stackoverflow.com/questions/15721764/….
  • Please check below answer in stackoverflow.com/a/18147860/2030100
  • What you describes also happens when a library adds new methods. In your explanation there is no reason not to inherit constructors. (Sorry for being blind)
  • @Orri It's not the same. It's a perfectly fine design choice for a certain subtype to require more information than its supertype before it can be constructed for the first time (because the type is known exactly at construction). But a method requiring more information to operate on a subtype than it needs to operate on a supertype is a design flaw (violation of LSP).
  • Constructors are not members, so they are not inherited by subclasses, but the constructor of the superclass can be invoked from the subclass.
  • Constructors are not inherited; they're chained.