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What is the main benefit of inheritance?
Reduces code duplication and makes code more maintainable by allowing subclasses to specialize superclass behavior without rewriting code.
Why are constructors not inherited?
Constructors are specific to the class and responsible for initializing the object's state, which may vary between superclasses and subclasses.
What determines the method executed during polymorphism?
The run-time type of the object, not the declared type, determines which method is executed.
Why override the toString() method?
To provide a human-readable string representation of an object's state, instead of the default memory reference.
What is the primary goal of Object-Oriented Programming?
To achieve abstraction, reduce code duplication, and increase code maintainability.
How does inheritance model real-world relationships?
By allowing classes to inherit properties and behaviors from more general classes, mirroring the structure of real-world objects and categories.
What is the significance of the Object class in Java?
It serves as the root of the class hierarchy, providing default implementations for essential methods and ensuring all objects share a common ancestor.
What is Dynamic Typing?
The method a computer executes on an object is determined by the run-time type of the object, not the declared type.
What is Static Typing?
The method a computer executes on an object is determined by the declared type of the object.
What is the benefit of using the super keyword?
The super keyword can be used to access the implementation in the Vehicle class, and then adds additional code to enable the car's cruise control system.
What is the output of the following code?
```java
class Animal {
public void makeSound() {
System.out.println("Generic animal sound");
}
}
class Dog extends Animal {
@Override
public void makeSound() {
System.out.println("Woof!");
}
}
Animal myAnimal = new Dog();
myAnimal.makeSound();
```
Woof!
Identify the error in the following code:
```java
class Animal {
private String name;
public Animal(String name) {
this.name = name;
}
}
class Dog extends Animal {
public Dog(String breed) {
this.breed = breed;
}
}
```
The Dog class constructor does not call the superclass constructor, and it attempts to access a non-existent 'breed' variable. It should call super(name) and accept the name parameter.
What is the output of the following code?
```java
class Vehicle {
int speed = 0;
public void accelerate() {
speed += 10;
}
}
class Car extends Vehicle {
@Override
public void accelerate() {
super.accelerate();
speed += 20;
}
}
Car myCar = new Car();
myCar.accelerate();
System.out.println(myCar.speed);
```
30
Identify the error in the following code:
```java
class Parent {
public void display() {
System.out.println("Parent class");
}
}
class Child extends Parent {
public int display() {
System.out.println("Child class");
return 0;
}
}
```
The Child class's display() method has a different return type (int) than the Parent class's display() method (void), making it an invalid override.
What is the output of the following code?
```java
class A {
public String toString() {
return "Class A";
}
}
class B extends A {
public String toString() {
return "Class B";
}
}
A obj = new B();
System.out.println(obj.toString());
```
Class B
Identify the error in the following code:
```java
class Animal {
public void eat() {
System.out.println("Animal eats");
}
}
class Dog extends Animal {
private void eat() {
System.out.println("Dog eats");
}
}
```
The Dog class's eat() method is private, making it not an override but a new method, and potentially inaccessible.
What is the output of the following code?
```java
class Parent {
public void method() {
System.out.println("Parent");
}
}
class Child extends Parent {
public void method(int x) {
System.out.println("Child");
}
}
Parent p = new Child();
p.method();
```
Parent
Identify the error in the following code:
```java
class Vehicle {}
class Car extends Vehicle {}
Car c = new Vehicle();
```
Cannot assign a Vehicle object to a Car reference. A superclass cannot be assigned to a subclass reference.
What is the output of the following code?
```java
class Base {
public void print() {
System.out.println("Base");
}
}
class Derived extends Base {
public void print() {
System.out.println("Derived");
}
}
Base b = new Derived();
b.print();
```
Derived
Identify the error in the following code:
```java
class Animal {
public Animal(String name) {
this.name = name;
}
String name;
}
class Dog extends Animal {
public void bark() {
System.out.println("Woof!");
}
}
```
Dog class must call the superclass constructor Animal(String name) using super(name) in its constructor.
How is inheritance applied in GUI frameworks?
GUI elements like buttons and text fields inherit from a base Widget or Component class, allowing them to share common properties and behaviors.
How is polymorphism used in database systems?
Different database drivers can be used through a common interface, allowing the application to interact with various database systems without code changes.
How is inheritance used in game development?
Game entities like characters and items inherit from a base Entity class, enabling code reuse and a structured game world.
How is polymorphism applied in collections?
Collections can store objects of different classes that implement a common interface, allowing for generic operations on diverse data types.
How is inheritance used in operating systems?
Different types of filesystems (e.g., FAT32, NTFS) can inherit from a base Filesystem class, providing a common interface for file operations.
How is polymorphism used in plugin architectures?
Plugins can implement a common interface, allowing the main application to interact with them in a uniform way, regardless of their specific implementation.
How is inheritance used in web frameworks?
Controllers and models can inherit from base classes, providing a structured way to handle web requests and data management.
How is polymorphism used in device drivers?
Different device drivers can implement a common interface, allowing the operating system to interact with them in a uniform way, regardless of the specific hardware.
How is inheritance used in scientific simulations?
Different types of particles or agents can inherit from a base Particle class, allowing for complex simulations with diverse behaviors.
How is polymorphism used in financial modeling?
Different types of financial instruments (e.g., stocks, bonds) can implement a common interface for valuation and risk analysis.