All Flashcards
What are the differences between a superclass and a subclass?
Superclass: More general, provides base functionality | Subclass: More specific, inherits from superclass and adds/modifies functionality.
What are the differences between inheritance and composition?
Inheritance: 'is-a' relationship, tight coupling | Composition: 'has-a' relationship, loose coupling.
What are the differences between method overriding and method overloading?
Overriding: Same method signature in subclass and superclass | Overloading: Same method name but different parameters in the same class.
What are the differences between single inheritance and multiple inheritance?
Single Inheritance: A class inherits from only one superclass | Multiple Inheritance: A class inherits from multiple superclasses (not supported in Java directly).
What are the differences between static and dynamic typing?
Static typing: Type checking at compile time | Dynamic typing: Type checking at runtime.
What are the differences between public and private members in the context of inheritance?
Public: Accessible from anywhere | Private: Only accessible within the class where they are defined, not inherited directly.
What are the differences between using 'extends' and 'implements' keywords?
'extends': Used for inheritance between classes | 'implements': Used for a class to implement an interface.
What are the differences between an abstract class and an interface?
Abstract Class: Can have method implementations and instance variables | Interface: Only method signatures (before Java 8) and constant variables.
What are the differences between inheritance and aggregation?
Inheritance: Creates a strong 'is-a' relationship, subclass depends on superclass | Aggregation: Creates a 'has-a' relationship, weaker dependency.
What are the differences between using inheritance and creating separate, unrelated classes?
Inheritance: Promotes code reuse, establishes hierarchical relationships | Separate Classes: No inherent relationship, can lead to code duplication.
What is the definition of Inheritance?
A mechanism where one class (subclass) acquires the properties (methods and instance variables) of another class (superclass).
What is the definition of a Superclass?
The class whose properties are inherited by another class.
What is the definition of a Subclass?
The class that inherits properties from another class (the superclass).
What is the definition of Polymorphism?
The ability of an object to take on many forms. Allows an object to be treated as an instance of its own class or its parent class.
What is the definition of Object-Oriented Programming (OOP)?
A programming paradigm based on the concept of 'objects', which contain data and code to manipulate that data.
What is the definition of Method Overriding?
When a subclass provides a specific implementation for a method that is already defined in its superclass.
What is the definition of the 'extends' keyword in Java?
A keyword used in Java to indicate that a class inherits from another class.
What is the definition of the 'super' keyword in Java?
A keyword used to access members of the superclass from within a subclass.
What is the Diamond Problem?
A problem that arises in multiple inheritance where a class inherits from two classes that have a common ancestor, leading to ambiguity in method resolution.
What is Dynamic Typing?
Type checking is done during run-time.
What is Static Typing?
Type checking is done during compile-time.
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'.