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?

<p>Protected (B)</p> Signup and view all the answers

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

<p>The Car class is a subclass of the FourWheeler class (C)</p> Signup and view all the answers

What is the output of the given program?

<p>Class Audi Class Car Class FourWheeler (C)</p> Signup and view all the answers

What is the purpose of an abstract method in Java?

<p>To declare a method that must be implemented by subclasses (B)</p> Signup and view all the answers

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

<p>Because it would prevent subclasses from overriding the method (A)</p> Signup and view all the answers

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

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

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

<p>The subclass will not compile (D)</p> Signup and view all the answers

What is the relationship between the Car and FourWheeler classes?

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

What happens when the Audi class constructor is called?

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

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

<p>To start the execution of the program (A)</p> Signup and view all the answers

What is the inheritance hierarchy of the classes?

<p>Audi -&gt; Car -&gt; FourWheeler (A)</p> Signup and view all the answers

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

<p>To print the class names during constructor calls (D)</p> Signup and view all the answers

What is the relationship between the Audi and Driver classes?

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

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

<p>ClassCastException (A)</p> Signup and view all the answers

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

<p>Because a parent object cannot be referred to by a child type reference (D)</p> Signup and view all the answers

What is the output of the given code?

<p>Runtime Error (A)</p> Signup and view all the answers

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

<p>To upcast an object of class A to class Trial (D)</p> Signup and view all the answers

Why does the code not throw a Compile Time Error?

<p>Because the code is syntactically correct (D)</p> Signup and view all the answers

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

<p>Trial object = new Trial(); (B)</p> Signup and view all the answers

What is the relationship between class A and class Trial?

<p>Class Trial is a subclass of class A (C)</p> Signup and view all the answers

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

<p>To extend a superclass (D)</p> 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.

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