Can we call subclass constructor from superclass constructor?

Category: technology and computing programming languages
4.4/5 (250 Views . 14 Votes)
5 Answers. A constructor from a subclass can call constructors from the superclass, but they're not inherited as such. because there's no Sub(int) constructor. It may be helpful to think of constructors as uninherited static methods with an implicit parameter of the object being initialized.

Then, how can a subclass constructor call a superclass constructor?

The constructors of the subclass can initialize only the instance variables of the subclass. Thus, when a subclass object is instantiated the subclass object must also automatically execute one of the constructors of the superclass. To call a superclass constructor the super keyword is used.

Beside above, can we inherit constructor of super class? 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. A constructor may only be called with new . It cannot be called as a method.

Beside this, can we call a superclass constructor from the class constructor?

Call to super() must be first statement in Derived(Student) Class constructor. If a constructor does not explicitly invoke a superclass constructor, the Java compiler automatically inserts a call to the no-argument constructor of the superclass. It is called constructor chaining..

Do you have to call super in constructor?

There is an implicit call to super() with no arguments for all classes that have a parent - which is every user defined class in Java - so calling it explicitly is usually not required. However, you may use the call to super() with arguments if the parent's constructor takes parameters, and you wish to specify them.

37 Related Question Answers Found

Can we use both this () and super () in a constructor?

So we can not have two statements as first statement, hence either we can call super() or we can call this() from the constructor, but not both. Both this() and super() are constructor calls, and constructor call must be the first (and only first) call in a constructor.

What is super () in Java?

super is a keyword. It is used inside a sub-class method definition to call a method defined in the super class. Private methods of the super-class cannot be called. It is also used by class constructors to invoke constructors of its parent class. Super keyword are not used in static Method.

What is constructor in OOP?

A constructor is a special method of a class or structure in object-oriented programming that initializes an object of that type. A constructor is an instance method that usually has the same name as the class, and can be used to set the values of the members of an object, either to default or to user-defined values.

How are this () and super () used with constructors?

How are this() and super() used with constructors? Constructors use this to refer to another constructor in the same class with a different parameter list. Constructors use super to invoke the superclass's constructor. If a constructor uses super, it must use it in the first line; otherwise, the compiler will complain.

Is super () necessary?

Calling exactly super() is always redundant. It's explicitly doing what would be implicitly done otherwise. That's because if you omit a call to the super constructor, the no-argument super constructor will be invoked automatically anyway.

Can constructor be extended?

Calling Constructors in Superclasses
In Java a class can extend another class. When a class extends another class it is also said to "inherit" from the class it extends. The class that extends is called the subclass, and the class being extended is called the superclass.

What is the difference between super and super () in Java?

Difference between super and super()
The super keyword in Java is a reference variable that is used to refer parent class objects. The super() in Java is a reference variable that is used to refer parent class constructors. super can be used to call parent class' variables and methods.

Can abstract class have constructor?

Yes, an abstract class can have a constructor in Java. You can either explicitly provide a constructor to abstract class or if you don't, the compiler will add default constructor of no argument in abstract class. This is true for all classes and it also applies to an abstract class.

Why super is used in constructor?

Usage of Java super Keyword
super can be used to refer immediate parent class instance variable. super can be used to invoke immediate parent class method. super() can be used to invoke immediate parent class constructor.

What is Polymorphism in Java?

Polymorphism in Java is a concept by which we can perform a single action in different ways. We can perform polymorphism in java by method overloading and method overriding. If you overload a static method in Java, it is the example of compile time polymorphism. Here, we will focus on runtime polymorphism in java.

What is static keyword in Java?

The static keyword in Java is used mainly for memory management. It is used with variables, methods, blocks and nested classes. It is a keyword that is used to share the same variable or method of a given class. This is used for a constant variable or a method that is the same for every instance of a class.

What is an interface?

In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hardware, peripheral devices, humans, and combinations of these.

What is overloading in Java?

Method Overloading is a feature that allows a class to have more than one method having the same name, if their argument lists are different. It is similar to constructor overloading in Java, that allows a class to have more than one constructor having different argument lists.

What is string in Java?

String is a sequence of characters, for e.g. “Hello” is a string of 5 characters. In java, string is an immutable object which means it is constant and can cannot be changed once it has been created.

Why super is first line in Java?

super() must be first because conceptually, the subclass instance "is-a" instance of the superclass, and must be a properly set-up superclass object. The superclass shouldn't need to know about the existence of subclasses, so it should be allowed to assume that its constructor is the first thing that runs.

Why is @override used in Java?

The @Override annotation indicates that the child class method is over-writing its base class method. It extracts a warning from the compiler if the annotated method doesn't actually override anything. It can improve the readability of the source code.

What is encapsulation in Java?

Encapsulation is one of the four fundamental OOP concepts. The other three are inheritance, polymorphism, and abstraction. Encapsulation in Java is a mechanism of wrapping the data (variables) and code acting on the data (methods) together as a single unit. Declare the variables of a class as private.