Object-Oriented Programming: Inheritance and Constructors

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Questions and Answers

What type of error will occur in the program if an abstract method is declared as final in an abstract class?

Runtime Error

Compile Time Error (correct)

Logic Error

Syntax Error

What is the purpose of an abstract class in Java?

To provide a way to override methods

To provide a base class that cannot be instantiated (correct)

To provide a blueprint for objects that can be instantiated

To provide a way to implement multiple inheritance

What will happen if a subclass does not implement an abstract method inherited from its superclass?

The subclass will throw a logic error

The subclass will compile successfully

The subclass will not compile (correct)

The subclass will throw a runtime exception

What is the access modifier of the display method in the FourWheeler class?

Protected Signup and view all the answers

What is the relationship between the Car class and the FourWheeler class?

The Car class is a subclass of the FourWheeler class Signup and view all the answers

What is the output of the given program?

Class Audi Class Car Class FourWheeler Signup and view all the answers

What is the purpose of an abstract method in Java?

To declare a method that must be implemented by subclasses Signup and view all the answers

Why can't an abstract method be declared as final in an abstract class?

Because it would prevent subclasses from overriding the method Signup and view all the answers

What is the purpose of the `super()` call in the `Audi` class constructor?

To call the constructor of the <code>Car</code> class Signup and view all the answers

What is the consequence of not implementing an abstract method in a subclass?

The subclass will not compile Signup and view all the answers

What is the relationship between the `Car` and `FourWheeler` classes?

The <code>Car</code> class is a subclass of the <code>FourWheeler</code> class Signup and view all the answers

What happens when the `Audi` class constructor is called?

The <code>Audi</code> class constructor and its superclass constructors are called Signup and view all the answers

What is the purpose of the `main` method in the `Driver` class?

To start the execution of the program Signup and view all the answers

What is the inheritance hierarchy of the classes?

Audi -> Car -> FourWheeler Signup and view all the answers

What is the role of the `System.out.println` statements in the constructors?

To print the class names during constructor calls Signup and view all the answers

What is the relationship between the `Audi` and `Driver` classes?

The <code>Audi</code> class is used by the <code>Driver</code> class Signup and view all the answers

What type of exception will be thrown by the line `Trial object = (Trial)new A();`?

ClassCastException Signup and view all the answers

Why does the line `Trial object = (Trial)new A();` throw an exception?

Because a parent object cannot be referred to by a child type reference Signup and view all the answers

What is the output of the given code?

Runtime Error Signup and view all the answers

What is the purpose of the line `Trial object = (Trial)new A();`?

To upcast an object of class A to class Trial Signup and view all the answers

Why does the code not throw a Compile Time Error?

Because the code is syntactically correct Signup and view all the answers

What is the correct way to create an object of class Trial?

Trial object = new Trial(); Signup and view all the answers

What is the relationship between class A and class Trial?

Class Trial is a subclass of class A Signup and view all the answers

What is the purpose of the `extends` keyword in the declaration of class Trial?

To extend a superclass Signup and view all the answers

Study Notes

Inheritance

Inheritance allows a class to inherit properties and behavior from another class, creating a parent-child relationship.
A child class can extend a parent class, inheriting its properties and behavior.

Constructors and Inheritance

When a child class is created, its constructor is called, followed by its parent's constructor.
The order of constructor calls is determined by the class hierarchy.
In the example, Audi class constructor calls Car class constructor, which in turn calls FourWheeler class constructor.

Abstract Classes and Methods

An abstract class can have abstract methods, which must be implemented by its child classes.
An abstract method cannot be declared as final.
In the example, Shape class has an abstract method calcArea() which cannot be declared as final.

Method Overriding

Method overriding occurs when a child class provides a different implementation for a method already defined in its parent class.
In the example, Trial class overrides test() method of A class.

Runtime Errors

A runtime error occurs when a program encounters an error during execution, rather than at compile time.
In the example, Trial object = (Trial)new A(); produces a runtime error because a parent object cannot be referred by a child type reference.

Compile Time Errors

A compile time error occurs when a program encounters an error during compilation, rather than at runtime.
In the example, the program produces a compile time error because the abstract method in the parent class has not found its implementation in the child class.

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Description

Learn about the concept of inheritance in object-oriented programming, including how child classes inherit properties and behavior from parent classes, and the role of constructors in this process.

Object-Oriented Programming: Inheritance and Constructors

Podcast Beta

Questions and Answers

What type of error will occur in the program if an abstract method is declared as final in an abstract class?

What is the purpose of an abstract class in Java?

What will happen if a subclass does not implement an abstract method inherited from its superclass?

What is the access modifier of the display method in the FourWheeler class?

What is the relationship between the Car class and the FourWheeler class?

What is the output of the given program?

What is the purpose of an abstract method in Java?

Why can't an abstract method be declared as final in an abstract class?

What is the purpose of the super() call in the Audi class constructor?

What is the consequence of not implementing an abstract method in a subclass?

What is the relationship between the Car and FourWheeler classes?

What happens when the Audi class constructor is called?

What is the purpose of the main method in the Driver class?

What is the inheritance hierarchy of the classes?

What is the role of the System.out.println statements in the constructors?

What is the relationship between the Audi and Driver classes?

What type of exception will be thrown by the line Trial object = (Trial)new A();?

Why does the line Trial object = (Trial)new A(); throw an exception?