All Flashcards
What is the purpose of the 'super(length, width, length, width);' line in the Rectangle constructor?
It calls the Quadrilateral constructor with the provided length and width values, effectively setting the sides of the rectangle.
java
public class Animal {
public Animal() {
System.out.println("Animal constructor");
}
}
public class Dog extends Animal {
public Dog() {
System.out.println("Dog constructor");
}
public static void main(String[] args) {
Dog d = new Dog();
}
}
What is the output of this code?
Animal constructor Dog constructor
java
public class A {
public A(int x) {
System.out.println("A: " + x);
}
}
public class B extends A {
public B() {
System.out.println("B");
}
public static void main(String[] args) {
B b = new B();
}
}
Identify the error in the following code.
The class A does not have a no-argument constructor. The class B's constructor needs to explicitly call A's constructor using super(value).
java
public class Parent {
public Parent(String name) {
System.out.println("Parent: " + name);
}
}
public class Child extends Parent {
public Child(String name) {
super(name);
System.out.println("Child: " + name);
}
public static void main(String[] args) {
Child c = new Child("Alice");
}
}
What is the output of this code?
Parent: Alice Child: Alice
java
public class Vehicle {
public Vehicle() {
System.out.println("Vehicle");
}
}
public class Car extends Vehicle {
// Complete the Car constructor to call the Vehicle constructor
public Car() {
// your code here
System.out.println("Car");
}
public static void main(String[] args) {
Car c = new Car();
}
}
Complete the Car constructor to call the Vehicle constructor.
super();
java
public class Base {
public Base(int x) {
System.out.println("Base: " + x);
}
}
public class Derived extends Base {
public Derived() {
super(5);
System.out.println("Derived");
}
public static void main(String[] args) {
Derived d = new Derived();
}
}
What is the output of this code?
Base: 5 Derived
java
public class Grandparent {
public Grandparent() {
System.out.println("Grandparent");
}
}
public class Parent extends Grandparent {
public Parent() {
System.out.println("Parent");
}
}
public class Child extends Parent {
public Child() {
System.out.println("Child");
}
public static void main(String[] args) {
Child c = new Child();
}
}
What is the output of this code?
Grandparent Parent Child
java
public class Device {
private String name;
public Device(String name) {
this.name = name;
}
}
public class Phone extends Device {
private String number;
public Phone(String name, String number) {
// Complete the constructor
this.number = number;
}
}
Complete the Phone constructor to call the Device constructor.
super(name);
java
public class Shape {
public Shape() {
System.out.println("Shape");
}
}
public class Circle extends Shape {
public Circle(int radius) {
System.out.println("Circle");
}
public static void main(String[] args) {
Circle c = new Circle(5);
}
}
What is the output of this code?
Shape Circle
java
public class Root {
public Root(int value) {
System.out.println("Root: " + value);
}
}
public class Branch extends Root {
public Branch() {
// Complete the constructor
System.out.println("Branch");
}
public static void main(String[] args) {
Branch b = new Branch();
}
}
Complete the Branch constructor to call the Root constructor with value 10.
super(10);
Why are constructors not inherited?
Constructors are specific to the class they are defined in and are responsible for initializing objects of that class.
What is the purpose of the 'super' keyword in a subclass constructor?
To call the constructor of the superclass, allowing reuse of initialization logic.
What happens if a subclass constructor doesn't explicitly call a superclass constructor?
Java automatically inserts a call to the superclass's no-argument constructor.
Why is it important to call the superclass constructor in a subclass?
To ensure that the superclass's instance variables are properly initialized.
Explain the constructor call chain in Java.
Subclass constructor calls superclass constructor, which may call its superclass constructor, and so on, up to the Object class constructor.
What is the role of the Object class in the constructor call chain?
It is the ultimate superclass, and its constructor is always the first to be called.
How does the 'super' keyword promote code reuse?
It allows subclasses to leverage the initialization logic already defined in the superclass constructor.
What is the significance of calling 'super' as the first statement in a subclass constructor?
It ensures that the superclass is initialized before any subclass-specific initialization takes place.
Explain how instance variables are initialized in a subclass when using 'super'.
Instance variables of the superclass are initialized by the superclass constructor, and subclass-specific instance variables are initialized separately in the subclass constructor.
What is the impact of not properly initializing the superclass when creating a subclass?
It can lead to unexpected behavior or errors due to uninitialized or incorrectly initialized superclass members.
How is the concept of calling superclass constructors applied in GUI frameworks?
When creating custom UI components, subclasses call the superclass constructor to initialize basic properties like size and position.
How is 'super' used in inheritance hierarchies for database entities?
Subclasses representing specific entity types call the superclass constructor to initialize common fields like ID and creation date.
How is the concept of calling superclass constructors applied when extending exception classes?
Custom exception classes call the superclass constructor to set the error message and other relevant information.
How is 'super' used when creating specialized data structures?
Subclasses of generic data structures (e.g., lists, trees) use 'super' to initialize the underlying data storage.
How is the concept of calling superclass constructors applied in game development?
When creating different types of game objects, subclasses call the superclass constructor to initialize common properties like position, health, and damage.
How is 'super' used in frameworks that implement design patterns like Template Method?
Subclasses call the superclass constructor to set up the basic structure of the algorithm, then implement specific steps in their own methods.
How is the concept of calling superclass constructors applied in web frameworks?
When creating custom controllers or models, subclasses call the superclass constructor to initialize framework-specific dependencies and configurations.
How is 'super' used in systems with plugin architectures?
Plugin classes call the superclass constructor to register themselves with the system and access core functionalities.
How is the concept of calling superclass constructors applied in scientific simulations?
When creating specialized simulation objects, subclasses call the superclass constructor to initialize common physical properties and simulation parameters.
How is 'super' used in embedded systems programming?
Subclasses representing specific hardware components call the superclass constructor to initialize device drivers and communication protocols.