9.1 What is inheritance?

Inheritance is like a family, except the kids only have one parent instead of two
For example:

The java code for it:

class Mom{
    // CODE
}
class Son extends Mom{
    // CODE
}
class Daughter extends Mom{
    // CODE
}

In this example, the Son and Daughter inherits the Mom, meaning it inherit the components of the mother. This makes the “Son” and “Daughter” classes the __ of the “Mom” class as they inherit the “Mom” class components and the “Mom” class the ___.

9.2 Using the Super keyword for Constructors

One keyword to know is the super keyword
The super keyword allows the subclass to store key variables in the main class’s constructor (also known as the super class)
Example below:

public class Vehicle { //This is the Superclass, it inherits the key variables for its subclasses
    public String Name; //They don't have to be public, but I just put public word for fun
    public String Sound;
    public int creation;
    public int Mph;
    public Vehicle(String name, int dateMade, String sound, int mph){ //Similar to the constructor used in Javascript. It maintains values within this superclass
        Name = name; 
        Sound = sound;
        creation = dateMade;
        Mph = mph;
    }
}

public class Car extends Vehicle {
    public int capacity;
    public Car(String name, int dateMade, String sound, int mph, int passangerCapacity){
        super(name, dateMade,sound, mph); //Uses the superclass's constructor to store the key variables for the Car subclass
        capacity = passangerCapacity;
    }
    public void Information(){ //Prints out the values the super class's constructors inherits
        System.out.println(super.Sound + " " + this.Sound);
        System.out.println("I am the " + super.Name);
        System.out.println("I was made in " + super.creation);
        System.out.println("I move at " + super.Mph +" miles per hour");
        System.out.println("I hold at most " + capacity + " people");
    }
}

public class Test {
    public static void main(String[] args){
        Car Tesla = new Car("Tesla", 2003, "VROOM!", 200, 5);
        Tesla.Information();
    }
}

Test.main(null);

VROOM! VROOM!
I am the Tesla
I was made in 2003
I move at 200 miles per hour
I hold at most 5 people

Popcorn Hack:

Make it so that a new instance of Bob runs

public class Worker {
    String name;
    int age;
    int salary;

    public Worker(String name, int age, int salary) {
        this.name = name;
        this.age = age;
        this.salary = salary;
    }
}

class financeWorker extends Worker { // dont confuse me plz
    String position;

    public financeWorker(String name, int age, int salary, String position) {
        super(name, age, salary);
        this.position = position;
    }

    public void Information() {
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Salary: " + salary);
        System.out.println("Position: " + position);
    }
}

public class Test {
    public static void main(String[] args) {
        financeWorker bob = new financeWorker("Askaht", 34, 15000009, "Quant");
        bob.Information();
    }
}
Test.main(null);

Name: Askaht
Age: 34
Salary: 15000009
Position: Quant

9.3 Overriding Methods

Method overriding is a concept in object-oriented programming (OOP) that allows a subclass to provide a specific implementation of a method that is already defined in its superclass. This enables a subclass to provide its own behavior for a method while maintaining a relationship with its superclass.

In the context Java, here’s how method overriding works:

Inheritance: Method overriding is closely related to inheritance. You have a superclass (or base class) and a subclass (or derived class). The subclass inherits properties and behaviors from the superclass.

Superclass Method: The superclass defines a method. This method can be overridden by the subclass.

Subclass Overrides: In the subclass, you can provide a new implementation of the same method. This is done by using the same method name, return type, and parameter list.

@Override Annotation (Java): In Java, it’s common to use the @Override annotation to explicitly indicate that a method in the subclass is intended to override a method in the superclass. This helps catch errors during compilation if the method doesn’t correctly match the superclass method signature.

Why Override Methods:

Method overriding is used for several reasons:

Customization: It allows you to customize or extend the behavior of a superclass method in the subclass to meet the specific needs of the subclass.

Polymorphism: Method overriding is a key component of polymorphism. It enables you to treat objects of the subclass as if they were objects of the superclass, promoting flexibility and extensibility.

Consistency: Method overriding helps maintain a consistent interface for classes in an inheritance hierarchy. Code that uses the superclass doesn’t need to be changed when a subclass overrides a method.

Code Reusability: It promotes code reusability by allowing you to build on existing code in the superclass.

class Animal {
    void makeSound() {
        System.out.println("Animals make sounds");
    }
}

class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Dog barks");
    }
}

class Cat extends Animal {
    @Override
    void makeSound() {
        System.out.println("Cat meows");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal animal = new Animal();
        Animal dog = new Dog();
        Animal cat = new Cat();

        animal.makeSound(); // Output: Animals make sounds
        dog.makeSound();    // Output: Dog barks
        cat.makeSound();    // Output: Cat meows
    }
}

Main.main(null);

Animals make sounds
Dog barks
Cat meows

In this example:

We have a base class Animal with a method makeSound().

We create two subclasses, Dog and Cat, which inherit from the Animal class.

Both Dog and Cat classes override the makeSound() method with their own implementations.

In the main method, we create instances of the base class and its subclasses.

We demonstrate polymorphism by calling the makeSound() method on objects of the base class and the subclasses. The method called depends on the actual type of the object, not the reference type.

This showcases how method overriding allows you to provide specific implementations for methods in subclasses, promoting polymorphism and custom behavior for each subclass.

Another Example:

Imagine you’re building a program to manage sports team rosters. You can have a base class ‘Athlete’ representing common attributes and actions of all athletes. Then, create subclasses for specific sports like ‘FootballPlayer’, ‘BasketballPlayer’, and ‘SoccerPlayer’.

// Base Class
class Athlete {
    String name;
    int age;
    int jerseyNumber;
    String position;

    public Athlete(String name, int age, int jerseyNumber, String position) {
        this.name = name;
        this.age = age;
        this.jerseyNumber = jerseyNumber;
        this.position = position;
    }

    public void train() {
        System.out.println(name + " is training.");
    }

    public void displayInfo() {
        System.out.println("Athlete Info:");
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Jersey Number: " + jerseyNumber);
        System.out.println("Position: " + position);
    }
}

Athlete athlete = new Athlete("John Mortensen", 19, 4, "Teacher");
athlete.train();
athlete.displayInfo();

John Mortensen is training.
Athlete Info:
Name: John Mortensen
Age: 19
Jersey Number: 4
Position: Teacher

class FootballPlayer extends Athlete {
    public FootballPlayer(String name, int age, int jerseyNumber, String position) {
        super(name, age, jerseyNumber, position);
    }

    @Override
    public void train() {
        System.out.println(name + " is practicing football drills.");
    }

    @Override
    public void displayInfo() {
        super.displayInfo();
    }
}

class BasketballPlayer extends Athlete {
    public BasketballPlayer(String name, int age, int jerseyNumber, String position) {
        super(name, age, jerseyNumber, position);
    }

    @Override
    public void train() {
        System.out.println(name + " is shooting 3s on the court.");
    }

    @Override
    public void displayInfo() {
        super.displayInfo();
    }
}

class SoccerPlayer extends Athlete {
    public SoccerPlayer(String name, int age, int jerseyNumber, String position) {
        super(name, age, jerseyNumber, position);
    }

    @Override
    public void train() {
        System.out.println(name + " is practicing taking free kicks.");
    }

    @Override
    public void displayInfo() {
        super.displayInfo();
    }
}

FootballPlayer footballPlayer = new FootballPlayer("Tyreek Hill", 28, 10, "Wide Receiver");
BasketballPlayer basketballPlayer = new BasketballPlayer("Jimmy Butler", 32, 22, "Small Forward");
SoccerPlayer soccerPlayer = new SoccerPlayer("Neymar Jr", 31, 10, "Left Winger");

footballPlayer.train();
footballPlayer.displayInfo();
System.out.println();

basketballPlayer.train();
basketballPlayer.displayInfo();
System.out.println();

soccerPlayer.train();
soccerPlayer.displayInfo();
System.out.println();

Tyreek Hill is practicing football drills.
Athlete Info:
Name: Tyreek Hill
Age: 28
Jersey Number: 10
Position: Wide Receiver



Jimmy Butler is shooting 3s on the court.
Athlete Info:
Name: Jimmy Butler
Age: 32
Jersey Number: 22
Position: Small Forward

Neymar Jr is practicing taking free kicks.
Athlete Info:
Name: Neymar Jr
Age: 31
Jersey Number: 10
Position: Left Winger

Explanation:

In this Java code, you have a basic “Athlete” class with information and actions that all athletes share. Then, there are specific types of athletes (football, basketball, and soccer players) that inherit these common traits but also have their unique behaviors, like training routines. Method overriding lets them have their own way of training while keeping the shared information, making the code easy to manage and reuse for different types of athletes.

Popcorn Hack:

Why is it helpful to have a common base class like ‘Athlete’ for all these different types of athletes? How does it make the code more organized?

It enhances the structure and clarity of the code, allowing for more flexibility and better data protection within the program.

9.4 Using Super keyword for Methods

Why only use super for constructors when you can use them for methods too?
With the super key word, not only can you store variables, but also store methods

class Animal{
    public void Introduction(String name){
        System.out.println("I am a " + name);
    }
}
class Dog extends Animal{ 
    public void Woof(){
        super.Introduction("Dog");//Inherits the introduction method in the Animal Class, then introduces itself as a dog
        System.out.println("Woof!"); //Does its own thing
    }
}
class Cow extends Animal{
    public void Moo(){
        super.Introduction("Cow");//Inherits the introduction method in the Animal Class, then introduces itself as a cow
        System.out.println("MOOOO!");//Does its own thing
    }
}
class Test{
    public static void main(String[] args){
        Dog dog = new Dog();
        Cow cow = new Cow();
        dog.Woof();
        cow.Moo();
    }
}
Test.main(null);

I am a Dog
Woof!
I am a Cow
MOOOO!

9.4 Hack

Finish up the code with this criteria: All subclasses must say their origin, the origin can be from SchoolSupply class, and it must run through main.

class SchoolSupply {
    public void BasicInfo(String name, String brand, String owner, int age) {
        System.out.println("I am a " + name);
        System.out.println("I am " + age + " years old");
        System.out.println("My owner is " + owner);
        System.out.println("My brand is " + brand);
    }
}

class Pencil extends SchoolSupply {
    public void Information(String brand, String owner, int age) {
        super.BasicInfo("Eraser", brand, owner, age);
    }
}

class Eraser extends SchoolSupply {
    public void Information(String brand, String owner, int age) {
        super.BasicInfo("Sharpener", brand, owner, age);
    }
}

public class Test {
    public static void main(String[] args) {
        Pencil pencil1 = new Pencil();
        pencil1.Information("Ticonderoga", "Askaht", 5);

        System.out.println();

        Eraser eraser1 = new Eraser();
        eraser1.Information("1995", "Vardaan", 2);
    }
}
Test.main(null);

I am a Eraser
I am 5 years old
My owner is Askaht
My brand is Ticonderoga

I am a Sharpener
I am 2 years old
My owner is Vardaan
My brand is 1995

9.5 Creating References Using Inheritance Hierarchies

Inheritance can be thought as an upside down tree with the root on the top and the leaves on the bottom. The root is the superclass while the leaves are the subclasses of this superclass. A visual representation of this tree is called a type diagram or hierarchy tree.

A sample structure would be like:

public class A
public class B extends A
public class C extends B
public class D extends C
public class E extends I
public class F extends I
public class G extends H
public class H extends A
public class I extends H

Popcorn Hack

Draw a hierarchy tree for the above structure and add the picture here

This structure works as C not only inherits properties from B, but it also inherits properties from A. B is like C’s parent and A is like C’s grandparent. Think about it like real life, all families inherit something from their ancestors.

In addition, you could also create objects like this:

C c = new C();
B c = new C();
A c = new C();

// This is the above example in code form

class A {}
class B extends A {}
class C extends B {}

public class Main {
    public static void main(String[] args) {
        C c = new C(); // variable c is of type C
        B b = new C(); // variable b is of type B, but refers to an instance of C
        A a = new C(); // variable a is of type A, but refers to an instance of C
    }
}

9.6 Polymorphism

A reference variable is polymorphic when it can refer to objects from different classes at different points in time

A reference variable can store a reference to its declared class or any subclass of it’s declared class

A method or operator are considered polymorphic when they are overwritten in at least one subclass

Polymorphism is the act of executing an overridden non-static method from the correct class at runtime based on the actual object type

Polymorphism allows code for a method call to be executed based on the class of the object referenced instead of the declared class

Example 1

Java polymorphism is mainly split into 2 types

Runtime Polymorphism

Process in which a function call to the overridden method is resolved at Runtime. This type of polymorphism is achieved by Method Overriding.

Compile Polymorphism

Also known as static polymorphism. This type is achieved by function overloading or operater overloading
Note: But java doesnt support Operator Overloading
When there are multiple functions with the same name but different parameters then these functions are said to be overloaded. Functions can be overloaded by changes in the number of arguments or/and a change in the type of arguments.

Here is an example of compile polymorphism

// Class 1
// Helper class
class Helper {
 
    // Method 1
    // Multiplication of 2 numbers
    static int Multiply(int a, int b)
    {
 
        // Return product
        return a * b;
    }
 
    // Method 2
    // // Multiplication of 3 numbers
    static int Multiply(int a, int b, int c)
    {
 
        // Return product
        return a * b * c;
    }
}
 
// Class 2
// Main class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
 
        // Calling method by passing
        // input as in arguments
        System.out.println(Helper.Multiply(2, 4));
        System.out.println(Helper.Multiply(2, 7, 3));
    }
}
GFG.main(null)

8
42

Example 2 & Popcorn Hack

Before executing cell, look at the example below. Think about which methods compiles? Which methods execute?

import java.util.Random;

public class Entertainer{
    private String talent;
    public Entertainer (String t){
        talent = t;
    }
    public String getTalent(){
        return talent;
    }
}

public class Comedian extends Entertainer{
    private ArrayList<String> jokes;
    public Comedian(String t, ArrayList<String> jks){
        super(t);
        jokes = jks;
    }
    public String getTalent(){
        return "Comedy style: " + super.getTalent();
    }
    public String tellJoke(){
        return jokes.get((int)(Math.random()*jokes.size()));
    }
}

// Which one of these will run? Which one of these will not? Comment out the line that isn't working and explain why
Entertainer kevin = new Entertainer("Musician");
System.out.println(kevin.getTalent());
//System.out.println(kevin.tellJoke());
// This line will not work because the tellJoke() method is not available in the Entertainer class

ArrayList<String> oneLiners = new ArrayList<String>(); 
// Add jokes to the list
oneLiners.add("Why did the programmer quit his job? Because he didn't get arrays."); 
oneLiners.add("Why did the developer go broke? Because he used up all his cache."); 

Entertainer soham = new Comedian("satire", oneLiners); 
System.out.println(soham.getTalent()); 
System.out.println(((Comedian)soham).tellJoke());

Musician
Comedy style: satire
Why did the developer go broke? Because he used up all his cache.

Example 3

Here is an example of runtime polymorphism

// Class 1
// Helper class
class Parent {
 
    // Method of parent class
    void Print()
    {
 
        // Print statement
        System.out.println("parent class");
    }
}
// Class 2
// Helper class
class subclass1 extends Parent {
 
    // Method
    void Print() { System.out.println("subclass1"); }
}
// Class 3
// Helper class
class subclass2 extends Parent {
 
    // Method
    void Print()
    {
 
        // Print statement
        System.out.println("subclass2");
    }
}
// Class 4
// Main class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
 
        // Creating object of class 1
        Parent a;
 
        // Now we will be calling print methods
        // inside main() method
 
        a = new subclass1();
        a.Print();
 
        a = new subclass2();
        a.Print();
    }
}
GFG.main(null)

subclass1
subclass2

9.7 Object Superclass

Now that we have learned about inheritance, what even allows our classes and objects that we have created to work the way they do? Where do the general characteristics of all objects come from? The answer lies in the object class.

The object class is the superclass of all other classes as well as arrays and other data types. The Object class is part of the java.lang package.

When we call a constructor to a “top-level class” that the coder hasn’t declared a superclass for, the Object constructor is implicitly called. In other words, the Object constructor is implicitly called when we call a constructor in a class that doesn’t explicitly extend another class. This will give the object some properties and methods that are common to all classes.

Example 1

public class Person {
    String name;
    int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public static void main(String[] args) {
        Person person1 = new Person("Jane Doe", 30);
        Person person2 = new Person("Jane Doe", 30);

        System.out.println(person1.equals(person1)); // Since person1 and person1 are the same object, the equals() method will return true
        System.out.println(person1.equals(person2)); // Since person1 and person2 are different objects, the equals() method will return false even though they have the same contents
    }
}

Person.main(null);

// The equals() method is inherited from the Object class
// By default, the equals() method in the Object class checks for object identity, which means it compares memory addresses to see if two references point to the exact same object
// In the code, person1 and person2 are distinct objects, so they have different memory addresses
// When we call person1.equals(person2), it checks if the memory addresses are the same (which they are not), so it returns false.

true
false

Example 2

public class Book {
    String title;
    String author;

    public Book(String title, String author) {
        this.title = title;
        this.author = author;
    }

    public static void main(String[] args) {
        Book book = new Book("The Catcher in the Rye", "J.D. Salinger");
        int hashCode = book.hashCode();
        System.out.println("HashCode: " + hashCode); // The output will be a unique integer value representing the object's hash code. The integer value will be different every time you run it
    }
}

Book.main(null);

// The hashCode() method in the Object class returns a unique integer value for each object
// This value is typically based on the object's memory address.
// In the code, when we call book.hashCode(), it generates a unique integer value representing the book object
// This value can be useful for various purposes, such as organizing objects in collections like HashMaps or HashSet where it helps in efficient retrieval of objects.

HashCode: 2094718255

Hacks

Popcorn Hacks (0.2): Participate in the discussion and fill in all of the blanks.
MC Questions (0.1): Answer the 10 MC questions below with short explanations
FRQ Hacks (0.5): Make a complex FRQ that involves everything we taught. Be sure to have a sample solution along with scoring guidlines and how the solution is scored.
Challenge (0.1): Make an example that uses everything we taught and it must run through main and uses input and output. Points will be awarded for complexity and creativity

MC Questions

Question 1 Question 2 Question 3 Question 4 Question 5 Question 6 Question 7 Question 8 Question 9 Question 10

The Car object will be successfully assigned to the reference variable vehicle of type Vehicle. Explanation: Java’s polymorphic capabilities ensure that a Car object can be referenced by a Vehicle type variable without any issues.

B c = new C(); Explanation: A C type object cannot be assigned to a B type variable because C is not a subclass of B.

The objects of class G can be treated as objects of class H and class J. Explanation: Due to Java’s polymorphism, objects of class G can be considered as instances of class H and class J because G inherits from both, directly or indirectly.

B is a subclass of C. Explanation: B is in the inheritance chain below C, meaning B inherits from C and thus, C type references can point to B objects.

There will be a compile time error. Explanation: A compile-time error occurs because Penguin is a more specific type than Bird, and Java does not allow a subclass type to be automatically treated as its superclass without explicit casting.

J j = new J(); options are all valid. Explanation: Any object of class K or L can be assigned to a variable of type J because they are both subclasses of J, which is in line with Java’s inheritance principles.

Polymorphism Explanation: Polymorphism in Java allows objects of subclasses to be referenced by variables of their superclass type.

H is an indirect superclass of G Explanation: H is an ancestor class to G in the class hierarchy, making it an indirect superclass.

The root is the superclass and the branches are the subclasses. Explanation: The superclass is the base from which subclasses diverge, similar to a tree’s root and branches.

The object will be successfully assigned to the reference variable Explanation: Subclass objects can be assigned to superclass reference variables due to Java’s polymorphic behavior.

FRQ (Free Response Question):

You are tasked with creating a simple simulation of a zoo that demonstrates the concepts of inheritance, polymorphism, method overriding, and the use of the super keyword. Your simulation should include the following:

A base class named Animal with:

A private field name of type String. A constructor that accepts a String to initialize the name field. A method makeSound() that prints out a generic sound. A method getName() that returns the name of the animal.

Two subclasses of Animal named Lion and Elephant that:

Override the makeSound() method to print out appropriate sounds for each animal. Have additional private fields unique to each animal (e.g., isAlpha for Lion, trunkLength for Elephant). Have constructors that call the superclass constructor with super() and initialize the unique fields. Include a displayInfo() method that prints out the animal’s name along with its unique properties.

A Zoo class that contains:

An ArrayList to hold Animal objects. A method addAnimal(Animal animal) to add new animals to the zoo. A method soundOff() that makes each animal in the zoo make its sound.

In your main method:

Create instances of Lion and Elephant. Add these instances to the Zoo. Call the soundOff() method to display the sounds of all animals in the zoo.

import java.util.ArrayList;

class Animal {
    private String name;

    public Animal(String name) {
        this.name = name;
    }

    public void makeSound() {
        System.out.println(this.name + " makes a sound.");
    }

    public String getName() {
        return this.name;
    }
}

class Lion extends Animal {
    private boolean isAlpha;

    public Lion(String name, boolean isAlpha) {
        super(name);
        this.isAlpha = isAlpha;
    }

    @Override
    public void makeSound() {
        System.out.println(getName() + " roars.");
    }

    public void displayInfo() {
        System.out.println(getName() + " is an alpha: " + this.isAlpha);
    }
}

class Elephant extends Animal {
    private double trunkLength;

    public Elephant(String name, double trunkLength) {
        super(name);
        this.trunkLength = trunkLength;
    }

    @Override
    public void makeSound() {
        System.out.println(getName() + " trumpets.");
    }

    public void displayInfo() {
        System.out.println(getName() + " has a trunk that is " + this.trunkLength + " feet long.");
    }
}

class Zoo {
    private ArrayList<Animal> animals = new ArrayList<>();

    public void addAnimal(Animal animal) {
        animals.add(animal);
    }

    public void soundOff() {
        for (Animal animal : animals) {
            animal.makeSound();
        }
    }
}

public class ZooSimulation {
    public static void main(String[] args) {
        Zoo zoo = new Zoo();
        
        Lion lion = new Lion("Leo", true);
        Elephant elephant = new Elephant("Ellie", 6.5);
        
        zoo.addAnimal(lion);
        zoo.addAnimal(elephant);
        
        zoo.soundOff();
    }
}

ZooSimulation.main(null);

Leo roars.
Ellie trumpets.

Scoring Guidelines:

1 point for creating the base class Animal with the correct field, constructor, and methods. 1 point for each subclass (Lion and Elephant) correctly extending Animal, overriding the makeSound() method, and adding unique fields with appropriate constructors. 1 point for the correct implementation of the displayInfo() method in subclasses. 1 point for creating the Zoo class with an ArrayList to store Animal objects and correctly implementing the addAnimal() and soundOff() methods. 1 point for the correct instantiation and use of Lion and Elephant objects in the main method, and adding them to the Zoo. Total: 6 points

How the Solution is Scored:

Full credit is given for a complete and correct implementation of each requirement. Partial credit may be awarded for incomplete implementations that demonstrate understanding of key concepts. No credit is given for sections that are incorrect or demonstrate a lack of understanding of the lesson’s concepts.

/**
 * This is a simple text-based Banking System.
 * It allows users to create accounts, deposit money, and withdraw money.
 * It demonstrates inheritance, polymorphism, method overriding, and the use of `super`.
 * Users can create either a Savings Account or a Checking Account.
 * The program outputs the account details and processes transactions.
 */

 import java.util.Scanner;

 // Base class for all bank accounts
 abstract class BankAccount {
     private String accountHolder;
     protected double balance;
 
     public BankAccount(String accountHolder, double initialBalance) {
         this.accountHolder = accountHolder;
         this.balance = initialBalance;
     }
 
     public abstract void deposit(double amount);
     public abstract void withdraw(double amount);
 
     public String getAccountHolder() {
         return accountHolder;
     }
 
     public double getBalance() {
         return balance;
     }
 
     protected void transactionSuccess(String transactionType, double amount) {
         System.out.println(transactionType + " of $" + amount + " was successful. Current balance: $" + balance);
     }
 }
 
 // Savings account with interest
 class SavingsAccount extends BankAccount {
     private double interestRate;
 
     public SavingsAccount(String accountHolder, double initialBalance, double interestRate) {
         super(accountHolder, initialBalance);
         this.interestRate = interestRate;
     }
 
     @Override
     public void deposit(double amount) {
         balance += amount;
         transactionSuccess("Deposit", amount);
     }
 
     @Override
     public void withdraw(double amount) {
         if (amount <= balance) {
             balance -= amount;
             transactionSuccess("Withdrawal", amount);
         } else {
             System.out.println("Insufficient funds for withdrawal.");
         }
     }
 
     public void addInterest() {
         double interest = balance * interestRate / 100;
         deposit(interest);
         System.out.println("Interest of $" + interest + " added.");
     }
 }
 
 // Checking account with overdraft
 class CheckingAccount extends BankAccount {
     private double overdraftLimit;
 
     public CheckingAccount(String accountHolder, double initialBalance, double overdraftLimit) {
         super(accountHolder, initialBalance);
         this.overdraftLimit = overdraftLimit;
     }
 
     @Override
     public void deposit(double amount) {
         balance += amount;
         transactionSuccess("Deposit", amount);
     }
 
     @Override
     public void withdraw(double amount) {
         if (balance + overdraftLimit >= amount) {
             balance -= amount;
             transactionSuccess("Withdrawal", amount);
         } else {
             System.out.println("Withdrawal amount exceeds overdraft limit.");
         }
     }
 }
 
 public class SimpleBankingSystem {
     public static void main(String[] args) {
         Scanner scanner = new Scanner(System.in);
         BankAccount account = null;
 
         System.out.println("Welcome to the Simple Banking System!");
         System.out.println("Would you like to create a 'savings' or 'checking' account?");
         String accountType = scanner.nextLine();
 
         System.out.println("Enter the name of the account holder:");
         String holderName = scanner.nextLine();
 
         System.out.println("Enter the initial balance:");
         double initialBalance = scanner.nextDouble();
 
         if ("savings".equalsIgnoreCase(accountType)) {
             System.out.println("Enter the interest rate (as a percentage):");
             double interestRate = scanner.nextDouble();
             account = new SavingsAccount(holderName, initialBalance, interestRate);
         } else if ("checking".equalsIgnoreCase(accountType)) {
             System.out.println("Enter the overdraft limit:");
             double overdraftLimit = scanner.nextDouble();
             account = new CheckingAccount(holderName, initialBalance, overdraftLimit);
         }
 
         if (account != null) {
             System.out.println("Account created successfully for " + account.getAccountHolder());
             System.out.println("Current Balance: $" + account.getBalance());
 
             // Perform transactions
             System.out.println("Would you like to 'deposit', 'withdraw', or 'exit'?");
             scanner.nextLine(); // Consume the leftover newline
             String action = scanner.nextLine();
 
             while (!"exit".equalsIgnoreCase(action)) {
                 System.out.println("Enter the amount:");
                 double amount = scanner.nextDouble();
 
                 if ("deposit".equalsIgnoreCase(action)) {
                     account.deposit(amount);
                 } else if ("withdraw".equalsIgnoreCase(action)) { 

Unit 9 Lesson • 74 min read

Description

9.1 What is inheritance?

9.2 Using the Super keyword for Constructors

Popcorn Hack:

9.3 Overriding Methods

Why Override Methods:

In this example:

Another Example:

Explanation:

Popcorn Hack:

9.4 Using Super keyword for Methods

9.4 Hack

9.5 Creating References Using Inheritance Hierarchies

Popcorn Hack

9.6 Polymorphism

Example 1

Example 2 & Popcorn Hack

Example 3

9.7 Object Superclass

Example 1

Example 2

Hacks

MC Questions