All Flashcards
What does the following code output?
java
class A {
public void printMessage() {
System.out.println("Class A");
}
}
class B extends A {
}
public class Main {
public static void main(String[] args) {
B b = new B();
b.printMessage();
}
}
Class A
Identify the error in the following code:
java
class Animal {
}
class Dog extends Animal, Pet {
}
Java does not support multiple inheritance of classes. A class can only extend one class. Remove either 'Animal' or 'Pet'.
What does the following code output?
java
class Vehicle {
public String modelName = "Generic Vehicle";
}
class Car extends Vehicle {
public String modelName = "Car Model";
public void displayModel() {
System.out.println(modelName);
}
public static void main(String[] args) {
Car myCar = new Car();
myCar.displayModel();
}
}
Car Model
Complete the code snippet to make 'Dog' a subclass of 'Animal':
java
class Animal {
}
class Dog ______ Animal {
}
extends
What does the following code output?
java
class Parent {
public void display() {
System.out.println("Parent class");
}
}
class Child extends Parent {
public void display() {
System.out.println("Child class");
}
}
public class Main {
public static void main(String[] args) {
Parent obj = new Child();
obj.display();
}
}
Child class
Identify the error in the following code:
java
class A {
private int x = 5;
}
class B extends A {
public void printX() {
System.out.println(x);
}
}
The instance variable 'x' in class 'A' is private and cannot be accessed directly from subclass 'B'.
What does the following code output?
java
class Animal {
public void makeSound() {
System.out.println("Generic animal sound");
}
}
class Dog extends Animal {
public void makeSound() {
System.out.println("Woof!");
}
}
public class Main {
public static void main(String[] args) {
Animal myAnimal = new Dog();
myAnimal.makeSound();
}
}
Woof!
Complete the following code to call the superclass's constructor:
java
class A {
public A(int x) {
}
}
class B extends A{
public B(int x){
______;
}
}
super(x);
What does the following code output?
java
class A {
public A() {
System.out.println("A");
}
}
class B extends A {
public B() {
System.out.println("B");
}
}
public class Main {
public static void main(String[] args) {
B b = new B();
}
}
A B
Identify the error in the following code:
java
class Animal {
public final void eat() {
System.out.println("Animal is eating");
}
}
class Dog extends Animal {
public void eat() {
System.out.println("Dog is eating");
}
}
The method 'eat()' in class 'Dog' cannot override the final method 'eat()' in class 'Animal'.
How is inheritance applied in GUI frameworks?
GUI components (e.g., buttons, text fields) are often created as subclasses of a base component class, inheriting common properties and behaviors.
How is inheritance used in creating different types of bank accounts?
A base 'Account' class can be a superclass for 'SavingsAccount' and 'CheckingAccount', inheriting common account properties and methods.
How can inheritance be applied in a game development context?
A base 'GameObject' class can be a superclass for different game entities like 'Player', 'Enemy', and 'Item', sharing common properties like position and collision detection.
How is inheritance applied in creating different types of employees in a company?
A base 'Employee' class can be a superclass for 'Manager', 'Developer', and 'SalesPerson', inheriting common employee attributes and methods.
How is inheritance used in representing different types of vehicles?
A base 'Vehicle' class can be a superclass for 'Car', 'Truck', and 'Motorcycle', inheriting common vehicle properties and methods.
How is inheritance applied in creating different shapes in a drawing application?
A base 'Shape' class can be a superclass for 'Circle', 'Rectangle', and 'Triangle', inheriting common properties like color and position.
How is inheritance used in representing different types of media files?
A base 'MediaFile' class can be a superclass for 'AudioFile', 'VideoFile', and 'ImageFile', inheriting common properties like file size and format.
How is inheritance applied in creating different types of users in a social media platform?
A base 'User' class can be a superclass for 'Admin', 'Moderator', and 'RegularUser', inheriting common user attributes and methods.
How is inheritance used in representing different types of geometric figures?
A base 'Figure' class can be a superclass for 'Square', 'Circle', and 'Triangle', inheriting common properties like area and perimeter calculations.
How is inheritance applied in creating different types of network connections?
A base 'Connection' class can be a superclass for 'WifiConnection', 'BluetoothConnection', and 'EthernetConnection', inheriting common connection properties and methods.
What is the primary benefit of using inheritance?
Code reusability. Subclasses inherit methods and instance variables from superclasses, reducing code duplication.
Why is inheritance considered a pillar of object-oriented programming?
Because it promotes abstraction and code organization by establishing hierarchical relationships between classes.
How does inheritance relate to the 'is-a' relationship?
A subclass 'is-a' more specific type of its superclass (e.g., 'APSubject is-a SchoolSubject').
What is the restriction on the number of superclasses a Java class can inherit from?
A Java class can only inherit from one superclass (single inheritance).
What is the role of polymorphism in OOP?
It allows objects of different classes to be treated as objects of a common type (usually a superclass), enabling flexibility and code extensibility.
How does method overriding contribute to polymorphism?
It allows subclasses to provide their own specific implementations of methods defined in the superclass, enabling different behaviors for the same method call.
Explain the concept of code reusability in inheritance.
Subclasses inherit the properties and methods of their superclasses, avoiding the need to rewrite the same code in multiple classes.
What is the significance of the Object class in Java's inheritance hierarchy?
It is the root of the class hierarchy. Every class in Java directly or indirectly inherits from the Object class.
What is the purpose of creating subclasses?
To create more specialized classes that inherit and extend the functionality of a more general superclass.
What is the difference between inheritance and composition?
Inheritance is an 'is-a' relationship, while composition is a 'has-a' relationship. Inheritance creates a tight coupling between classes, while composition promotes loose coupling.