OOP Principles: Abstraction, Encapsulation, Polymorphism

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Questions and Answers

Which principle of OOP focuses on representing essential features without including background details or complexity?

Abstraction (correct)
Encapsulation
Inheritance
Polymorphism

Which of the following is NOT a characteristic of abstraction in object-oriented programming?

Reduces complexity.
Simplifies design.
Focuses on essential qualities.
Focuses on specific implementation details. (correct)

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

To allow direct access to data members from outside the class.
To bind code and data together and protect them from misuse. (correct)
To inherit properties from a parent class.
To define multiple methods with the same name but different signatures.

Which mechanism is commonly used to implement encapsulation in Java?

Using private access modifiers and getter-setter methods (D) Signup and view all the answers

In the context of polymorphism, what distinguishes method overloading from method overriding?

Overloading involves methods with the same name but different signatures in the same class, while overriding involves methods with the same name and signature in different classes. (C) Signup and view all the answers

Which type of polymorphism is achieved by method overriding?

Dynamic polymorphism (C) Signup and view all the answers

Consider a class `Calculator` with methods `add(int a, int b)` and `add(int a, int b, int c)`. What OOP principle is being demonstrated?

Polymorphism (B) Signup and view all the answers

If a superclass has a method `display()` and a subclass overrides this method, which version of `display()` is called when an object of the subclass is used?

The subclass's <code>display()</code> method. (D) Signup and view all the answers

What is the implication of declaring a class as `final` in Java?

It prevents the class from being extended (inherited). (B) Signup and view all the answers

When is a `static` variable or method associated in Java?

With the class itself, regardless of any instances. (D) Signup and view all the answers

In the context of a ticket booking system, why might `TOTAL_TICKETS` be declared as a `static` variable?

To maintain a single, shared count of the remaining tickets available across all users and windows. (B) Signup and view all the answers

Which of the following statements is true regarding `static` methods in interfaces, starting from Java 8?

They can be called directly using the interface name. (B) Signup and view all the answers

Given a `final` class `CharacterUtility`, what will happen if you try to create a subclass `MyCharacterUtility` that extends `CharacterUtility`?

The compiler will produce an error, indicating that you cannot extend a <code>final</code> class. (D) Signup and view all the answers

What is the primary role of a constructor in Java?

To initialize an object immediately upon its creation. (C) Signup and view all the answers

If a class does not explicitly define a constructor, what does Java do?

Automatically supplies a default constructor. (D) Signup and view all the answers

What is the significance of the `new` keyword in the statement `objA = new A();`?

It allocates memory for the new object of class <code>A</code>. (B) Signup and view all the answers

Why do constructors not have a return type, not even `void`?

The implicit return type of a constructor is the class type itself. (C) Signup and view all the answers

Consider a class `Animal` with a parameterized constructor. Which of the following statements correctly creates an object of `Animal` passing the required argument?

<code>Animal obj = new Animal("Dog");</code> (A) Signup and view all the answers

In Java, what happens to private members of a class when a subclass inherits from it?

The subclass does not inherit the private members at all. (A) Signup and view all the answers

Analyze the following code snippet:

public class Animal {
    public Animal() {
        System.out.println("Animal constructor");
    }
}

public class Mammal extends Animal {
    public Mammal() {
        System.out.println("Mammal constructor");
    }
}

public class Main {
    public static void main(String[] args) {
        new Mammal();
    }
}

What will be the correct output?

<code>Animal constructor Mammal constructor</code> (A) Signup and view all the answers

Which of the following statements regarding object creation in Java is most accurate?

The <code>new</code> operator and the constructor work together to allocate memory and initialize the object, and the assignment operator assigns the object's address to a reference. (C) Signup and view all the answers

What is the primary purpose of the `super()` keyword when used as the first statement in a subclass constructor?

To explicitly invoke a specific constructor (parameterized or non-parameterized) of the immediate superclass. (B) Signup and view all the answers

If a subclass constructor does not explicitly call `super()`, what happens implicitly?

The non-parameterized constructor of the immediate superclass is called implicitly. (D) Signup and view all the answers

In what scenario would you use `super()` within a method in a subclass?

To invoke the overridden version of a method in the immediate superclass. (D) Signup and view all the answers

What is the consequence of using `super()` with arguments that do not match any of the superclass constructors?

The compiler will generate an error indicating that no matching constructor was found. (B) Signup and view all the answers

What is the purpose of the `this` keyword?

Refers to the current instance of the class. (C) Signup and view all the answers

Consider a scenario where a local variable in a constructor has the same name as an instance variable. How can you correctly initialize the instance variable?

By using the <code>this</code> keyword to refer to the instance variable. (D) Signup and view all the answers

What is constructor overloading?

Having multiple constructors in a class with different signatures (different number or types of parameters). (C) Signup and view all the answers

How does the compiler determine which overloaded constructor to call when an object is created?

Based on the number and types of arguments passed during object creation. (D) Signup and view all the answers

When a naming conflict arises between a local variable and an instance variable within a class, how can you specifically refer to the instance variable?

Employ the <code>this</code> keyword to refer to the instance variable. (D) Signup and view all the answers

What is the primary purpose of using `this()` within a constructor in Java?

To invoke a different constructor of the same class. (B) Signup and view all the answers

Which of the following statements accurately describes parameter passing in Java?

Java exclusively uses call by value for both primitive types and objects, but objects are handled differently. (C) Signup and view all the answers

In the context of the Student class with attributes like `rollNbr`, `name`, and `courses`, what is the purpose of a parameterized constructor?

To initialize the attributes of a newly created Student object with provided values. (D) Signup and view all the answers

Consider a `Marksheet` class with a `calculateGrade()` method. If the method is overloaded to accept a `Student` object, what advantage does this provide?

It enables the Marksheet class to calculate the grade based on the student's overall performance data encapsulated within the Student object. (C) Signup and view all the answers

Within the `Marksheet` class, the calculateGrade() method determines a student's grade based on their percentage. Which grade is assigned if a student's percentage is 72%?

E (Excellent) (C) Signup and view all the answers

If you modify the `rollNbr` of a `Student` object passed as an argument to the `calculateGrade()` method in `Marksheet`, what happens to the original `Student` object's `rollNbr` outside the method?

The original Student object's <code>rollNbr</code> is also modified to reflect the change made inside the method. (A) Signup and view all the answers

Consider the `printMarksheet()` method in the `Marksheet` class. What is its primary responsibility?

To display the calculated percentage and grade of the student. (A) Signup and view all the answers

Why do instance variables sometimes not receive the values assigned to local variables within a constructor, even when initialization is attempted?

Local variables have scope limited to the method they're defined in, and can hide instance variables with the same name, preventing assignment. (C) Signup and view all the answers

What is the primary purpose of the `this` keyword in Java regarding instance variables and local variables?

To explicitly refer to the current object's instance variables, especially when they have the same name as local variables. (C) Signup and view all the answers

Consider a `Dog` class with an instance variable `tailLength` and a constructor `Dog(double tailLength)`. Without the `this` keyword, what happens when the constructor attempts to assign the parameter `tailLength` to the instance variable `tailLength`?

The parameter <code>tailLength</code> is assigned to itself, leaving the instance variable uninitialized or with its default value. (D) Signup and view all the answers

In a scenario where both an instance variable and a local variable share the same name within a class, how does Java typically resolve this naming conflict?

The local variable takes precedence within its scope, effectively hiding the instance variable. (D) Signup and view all the answers

Given a class `Animal` with an instance variable `name`, and a constructor `Animal(String name)`, which of the following code snippets correctly assigns the constructor's parameter to the instance variable, avoiding naming conflicts?

<code>this.name = name;</code> (C) Signup and view all the answers

Which of the following statements accurately describes the behavior of the `this` keyword in Java?

<code>this</code> refers to the current object of the class. (D) Signup and view all the answers

In a `Car` class, both the instance variable and the constructor parameter for model name are named `modelName`. If the `this` keyword is omitted during assignment in the constructor, what is the likely outcome?

Only the local parameter <code>modelName</code> will be affected, leaving the instance variable uninitialized, as local variable hides the instance variable. (D) Signup and view all the answers

When should you use the `this` keyword when dealing with instance variables and local variables in a method or constructor?

When the local variable has the same name as the instance variable, and you want to access/modify the instance variable. (B) Signup and view all the answers

Flashcards

Abstraction

Focusing on essential qualities, discarding irrelevant details. Achieved through data and process means.

Encapsulation

Bundling code & data. Protects from misuse through controlled interfaces.