FRQs

Question 2 - Writing Classes:

(a) Describe the different features needed to create a class and what their purpose is.

Class Name: identifies the class, use for constructor later
Instance Variables: store data in the object
Methods: define functions of class
Constructor: instantiate an object of the class
Encapsulation: public (anywhere), private (within class), protected (within class and subclass): (defines scope for the class/visibiltiy)
Inheritance: allows class to inherit data/methods from other classes
Polymorphism: allows objects of different classes to be treated as part of one superclass
Abstraction: hides implementation details of an object

(b) Code:

Create a Java class BankAccount to represent a simple bank account. This class should have the following attributes:

accountHolder (String): The name of the account holder.
balance (double): The current balance in the account.

Implement the following mutator (setter) methods for the BankAccount class:

setAccountHolder(String name): Sets the name of the account holder.
deposit(double amount): Deposits a given amount into the account.
withdraw(double amount): Withdraws a given amount from the account, but only if the withdrawal amount is less than or equal to the current balance. Ensure that the balance is never negative.

public class BankAccount {

    // Attributes
    private String accountHolder;
    private double balance;

    // Constructor
    public BankAccount(String accountHolder, double balance) {
        this.accountHolder = accountHolder;
        if (balance >= 0) {
            this.balance = balance;
        } else {
            System.out.println("Initial balance cannot be negative. Setting balance to 0.");
            this.balance = 0;
        }
    }

    // Setter name for account holder
    public void setAccountHolder(String name) {
        this.accountHolder = name;
    }

    // Deposit method
    public void deposit(double amount) {
        if (amount > 0) {
            this.balance += amount;
            System.out.println(amount + " deposited successfully.");
        } else {
            System.out.println("Invalid amount. Deposit amount should be greater than 0.");
        }
    }

    // Withdraw method
    public void withdraw(double amount) {
        if (amount > 0) {
            if (amount <= this.balance) {
                this.balance -= amount;
                System.out.println(amount + " withdrawn successfully.");
            } else {
                System.out.println("Insufficient balance. Withdrawal amount exceeds the current balance.");
            }
        } else {
            System.out.println("Invalid amount. Withdrawal amount should be greater than 0.");
        }
    }

    // Getter method for balance
    public double getBalance() {
        return this.balance;
    }

    // Main method to test the BankAccount class
    public static void main(String[] args) {
        // Creating a BankAccount object
        BankAccount account = new BankAccount("John Doe", 1000);

        // Display initial balance
        System.out.println("Initial balance: " + account.getBalance());

        // Depositing and withdrawing money
        account.deposit(500);
        account.withdraw(200);
        account.withdraw(1500);  // This withdrawal should fail due to insufficient balance

        // Display updated balance
        System.out.println("Updated balance: " + account.getBalance());
    }
}
BankAccount.main(null);

Initial balance: 1000.0
500.0 deposited successfully.
200.0 withdrawn successfully.
Insufficient balance. Withdrawal amount exceeds the current balance.
Updated balance: 1300.0

Question 3 - Instantiation of a Class

(a) Explain how a constructor works, including when it runs and what generally is done within a constructor.

Allows instantiation of a class to make an object of the class using new keyword
Can take in parameters to give initial values of the object
Use super to access superclass and this to access construtors in the class
Can be static or non-static to access these values without making an object of the class

(b) Create an example of an overloaded constructor within a class. You must use at least three variables. Include the correct initialization of variables and correct headers for the constructor. Then, run the constructor at least twice with different variables and demonstrate that these two objects called different constructors.

public class SchoolMember {

    // Instance variables
    private String memberName;
    private int memberAge;
    private String memberPosition;

    // Constructor with memberName parameter
    public SchoolMember(String memberName) {
        this.memberName = memberName;
        this.memberAge = 0; 
        this.memberPosition = "None"; 
        System.out.println("Constructor with memberName parameter called.");
    }

    // Constructor with memberName and memberAge parameters
    public SchoolMember(String memberName, int memberAge) {
        this.memberName = memberName;
        this.memberAge = memberAge;
        this.memberPosition = "None";   // Default memberPosition
        System.out.println("Constructor with memberName and memberAge parameters called.");
    }

    // Constructor with memberName, memberAge, and memberPosition parameters
    public SchoolMember(String memberName, int memberAge, String memberPosition) {
        this.memberName = memberName;
        this.memberAge = memberAge;
        this.memberPosition = memberPosition;
        System.out.println("Constructor with memberName, memberAge, and memberPosition parameters called.");
    }

    // Getter methods
    public String getMemberName() {
        return memberName;
    }

    public int getMemberAge() {
        return memberAge;
    }

    public String getMemberPosition() {
        return memberPosition;
    }

    // Main method to test the SchoolMember class
    public static void main(String[] args) {
        // Creating SchoolMember objects using different constructors
        SchoolMember member1 = new SchoolMember("John");
        SchoolMember member2 = new SchoolMember("Jane", 30);
        SchoolMember member3 = new SchoolMember("Doe", 25, "Teacher");

        // Displaying the details of the created SchoolMember objects
        System.out.println("Member1 details - Name: " + member1.getMemberName() + ", Age: " + member1.getMemberAge() + ", Position: " + member1.getMemberPosition());
        System.out.println("Member2 details - Name: " + member2.getMemberName() + ", Age: " + member2.getMemberAge() + ", Position: " + member2.getMemberPosition());
        System.out.println("Member3 details - Name: " + member3.getMemberName() + ", Age: " + member3.getMemberAge() + ", Position: " + member3.getMemberPosition());
    }
}
SchoolMember.main(null);

Constructor with memberName parameter called.
Constructor with memberName and memberAge parameters called.
Constructor with memberName, memberAge, and memberPosition parameters called.
Member1 details - Name: John, Age: 0, Position: None
Member2 details - Name: Jane, Age: 30, Position: None
Member3 details - Name: Doe, Age: 25, Position: Teacher

Workshop 2 Hacks • 14 min read

FRQs

Question 2 - Writing Classes:

Question 3 - Instantiation of a Class