Object-Oriented Programming Basics

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Questions and Answers

What is a characteristic of an abstract class?

It requires all methods to be implemented in the same class.

It can contain constructors but cannot be instantiated. (correct)

It must contain at least one concrete method.

It can be instantiated directly.

What is true about interfaces before JDK 8?

Interfaces can be instantiated like classes.

All methods in interfaces must be public and abstract. (correct)

Interfaces can contain non-abstract methods.

Only one interface can be implemented by a class.

Which keyword must a concrete class use to inherit from an abstract class?

abstracts

implements

inherits

extends (correct)

What must a concrete class do when it implements an interface?

Implement all abstract methods defined in the interface. Signup and view all the answers

Which aspect of interfaces helps achieve multiple inheritance behavior?

Classes can implement interfaces regardless of their class hierarchy. Signup and view all the answers

What is the primary purpose of abstraction in object-oriented programming?

To expose only essential characteristics and behaviors Signup and view all the answers

Which feature of object-oriented programming prevents access to the internal state of an object?

Encapsulation Signup and view all the answers

In which scenario is inheritance primarily utilized?

When a new class has common attributes with an existing class Signup and view all the answers

What is a key benefit of encapsulation in object-oriented programming?

It enables easy modification of implemented code without affecting other code Signup and view all the answers

Which of the following statements is NOT true about inheritance?

Constructors are inherited by subclasses Signup and view all the answers

What does polymorphism in object-oriented programming allow developers to do?

Use a single interface to represent different data types Signup and view all the answers

Which feature of object-oriented programming is specifically referred to as data hiding?

Encapsulation Signup and view all the answers

What type of class is derived from another class in object-oriented programming?

Sub class Signup and view all the answers

What is true about the relationship between the Corolla class and the ToyotaCar class?

Corolla extends ToyotaCar, making ToyotaCar its superclass. Signup and view all the answers

What is the purpose of the keyword 'this' in the Corolla constructor?

It calls another constructor in the same class with different parameters. Signup and view all the answers

Which statement correctly describes the 'super' keyword?

It is used to reference superclass members in subclasses. Signup and view all the answers

What will happen if the Corolla class does not explicitly call a superclass constructor?

It will implicitly call the default constructor of its direct superclass, ToyotaCar. Signup and view all the answers

When a static method is defined in the Corolla class, which keyword cannot be used within that method?

this Signup and view all the answers

What is the initial value assigned to 'engineCapacity' in the Corolla class?

1500 Signup and view all the answers

What will the printInfo method display when called on a Corolla instance with default values?

Brand: Toyota, Model: Corolla 141, Engine Capacity: 1500 Signup and view all the answers

Which of the following statements is true regarding single inheritance in Java?

A class can only inherit from one direct superclass. Signup and view all the answers

What does the 'super' keyword allow a subclass to do in Java?

Invoke a constructor of the superclass Signup and view all the answers

Which statement about method overloading is true?

Overloaded methods must differ in the number or type of parameters. Signup and view all the answers

Why is the following constructor incorrect? public Corolla() { super(); this(1500, "Corolla 141"); }

The 'super()' call is out of order. Signup and view all the answers

What type of polymorphism is achieved through method overloading?

Static polymorphism Signup and view all the answers

In the context of polymorphism, what does dynamic method binding refer to?

It allows methods to be called without knowing the class type. Signup and view all the answers

Which of the following correctly describes a characteristic of the Corolla class?

It inherits the color attribute directly from ToyotaCar. Signup and view all the answers

What will be printed when the printInfo method of the Corolla class is called?

Brand : White Model : Corolla 141 Engine Capacity : 1500 Signup and view all the answers

What must a method do to properly implement overriding in Java?

Have the same return type and parameters as the method in the superclass. Signup and view all the answers

What is the primary reason for overloading methods in Java?

To allow the same method name to accept different parameters. Signup and view all the answers

Which statement is true regarding method overriding?

Overridden methods can have the same signature in a subclass. Signup and view all the answers

What does dynamic binding in Java allow during runtime?

Resolution of method calls based on the object type encountered at runtime. Signup and view all the answers

In the context of constructors, what is constructor overloading?

Defining multiple constructors with different parameter lists. Signup and view all the answers

What is the result of calling the `start()` method in the `Vitz2009` class?

It will print 'Keep the key with you and push start button'. Signup and view all the answers

What is the purpose of the `super` keyword in Java?

To call methods or constructors from a superclass. Signup and view all the answers

In the `Super` and `Sub` classes, how does `Sub` handle method `m1()`?

The <code>Sub</code> class uses <code>super.m1()</code> to call the <code>Super</code> class method. Signup and view all the answers

What will happen if you try to override a final method in a subclass?

The program will not compile due to an error. Signup and view all the answers

Which of the following statements about method overloads is false?

Overloaded methods can differ in return type. Signup and view all the answers

Study Notes

Object-Oriented Programming (OOP)

Every class in Java extends the Object class unless specified otherwise.
this keyword, in methods, refers to the current instance of the class.
this, in constructors, is used to call another constructor within the same class.
super keyword, used in methods, refers to the superclass to execute an overridden method.
super, used in constructors, calls a constructor of the superclass.
Important: this() and super() cannot be used together in the same constructor.

7 Basic Features of OOP

Abstraction: Focusing on essential characteristics and behaviors hiding unnecessary details.
Encapsulation: Protecting data and methods from external access, achieved by declaring fields as private.
Inheritance: A subclass inherits properties and methods from a superclass, allowing code reuse.
Polymorphism: Ability of a method to perform different tasks based on the object it's acting upon.

Polymorphism Types

Overloading: Defining multiple methods with the same name but different parameter lists.
Overriding: Redefining a method in a subclass with the same signature as the superclass method.
Dynamic Binding: Resolving subclass method references at runtime.

Abstract Classes

Abstract classes contain zero or more abstract methods, which need to be implemented by concrete subclasses.
Abstract classes cannot be instantiated, but they can have constructors.

Interfaces

Interfaces define a standard contract for classes to implement, specifying behavior.
All methods in an interface are public and abstract.
Concrete classes must implement all abstract methods defined in an interface.
Interfaces allow multiple inheritance behavior in Java.

Method Overloading Rules

Overloaded methods must have different parameter lists in terms of type, number, or both.
Return type alone is insufficient for method overloading.
Overloaded methods can have different return types.

Method Overriding Rules

Overridden methods have the same signature.
Subclass definition is used for overridden methods.
The overridden method must have less restrictive access modifiers.
The overridden method cannot throw more checked exceptions.
The return type of the overridden method must be the same or a subtype of the original return type.

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Description

Test your knowledge on the fundamentals of Object-Oriented Programming (OOP) in Java. This quiz covers key concepts such as classes, methods, inheritance, and polymorphism, along with the significance of keywords like this and super. Enhance your understanding of OOP principles and their applications.