Question

As an object oriented language, Java obviously provides support for composition and inheritance. Let's start off by describing how Java specifies that one class inherits from another class. Are there any restrictions on inheritance in Java that distinguish it from C++? How does a derived class override a base class method? How does an overridden method invoke a base class method? How does the derived class constructor invoke an explicit value constructor from the base class? Note: Plagiarism is checked

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Answer 1

Inheritance is one of the important feature in OOP. Inheritance says that the child can inherit the features of Parent, here child acts as derived class and parent acts as base class.

Lets see how Inheritance works in Java.

In java, the child class or the derived class inherit the parent or base class features by using "extends" keyword.

For Example:

Class Child extends Parent
{

}

Here class Child inherits the features of Parent.

Are there any restrictions in inheritance in Java that distinguish C++?

In Java multiple inheritance is not allowed through classes which means that derived class cannot inherit features of more than one base class.

By default every class is inherited from the Object class in Java and whereas in C++ it doesn't inherit anything.

This can be done through interfaces in Java. Derived Interfaces use implements keyword to inherit the features from the base interfaces

For Example:

Interface Abc implements Def, Ghi

How does a derived class override a base class in java?

Consider a base class Shape and a derived class Rectangle. Both have a method called draw().

Class Shape
{

public void draw()
{

}

}

Class Rectangle extends Shape
{

public void draw()
{

}

public static void main(String[] args)
{
Shape s= new Rectangle(); // Here we are creating a derived class object and asssigning it to base class reference. JVM will decide which objectto call during runtime.
s.draw(); // The reference is base class but draw method gets overrided during runtime as derived class object is assigned to base class

}

}

How does a overriden method invoke a base class method?

In derived class method call base class method by using Super keyword.

draw() // method in Rectangle class
{

super.draw(); // This will invoke base class method
}

How does the derived class constructor invoke an explicit value constructor from the base class in java?

// Shape class Constructor

Shape(int area)
{
this.area=area;
}

To invoke this base class constructor in the derived class constructor, use super keyword in Rectangle class

// Rectangle class constructor

Rectangle(int area)
{

super(area);

}

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