Lesson 31 of 31

8 mins read

Capstone Mini Projects

In Plain English

Congratulations on reaching the capstone module! In this final lesson, you will put everything you've learned into practice—variables, operators, branching, loops, arrays, OOP, and methods—by exploring complete, production-grade Java mini-projects.

The Mental Model

"You have gathered all the individual Lego bricks: types, loops, logic, and classes. Now you get to assemble them into a working spaceship."

Deep Dive: How It Works

Project 1: Bank Account Simulator (OOP, encapsulation, deposit/withdraw methods, balance checks).

Project 2: Student Grade Analytics (Arrays, loops, averages, letter grade mapping).

Project 3: Number Guessing Simulation (Conditionals, loops, counters).

Syntax Blueprint

class BankAccount {
    private double balance;
    void deposit(double amount) { balance += amount; }
}

Combine state encapsulation, methods, and control flow in complete programs.

Core Rules to Remember

Architectural Thinking: Separate data representation (classes) from application flow (main).

Edge Case Handling: Validate balances, zero checks, and boundary conditions.

Ready for Next Steps: You now possess the foundational skills to build real Java applications.

Common Beginner Traps & How to Fix Them

Mistake:Putting all code in a single monolithic main method

Why it happens: Quick prototyping can lead to messy code.

How to fix: Decompose code into classes and methods with clear responsibilities.

Pro Tip: Experiment by modifying the code directly in ZenCompiler and hitting Run Code!

Live Interactive Example

Hit Run Code to see it live

Full Bank Account Simulator

Java 13

class BankAccount {
    String accountHolder;
    double balance;

BankAccount(String holder, double initialDeposit) {
        this.accountHolder = holder;
        this.balance = initialDeposit;
    }

void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
            System.out.println("Deposited $" + amount + " | New Balance: $" + balance);
        }
    }

void withdraw(double amount) {
        if (amount > balance) {
            System.out.println("Declined: Insufficient funds for $" + amount);
        } else {
            balance -= amount;
            System.out.println("Withdrew $" + amount + " | Remaining: $" + balance);
        }
    }
}

public class Main {
    public static void main(String[] args) {
        BankAccount account = new BankAccount("Alex Rivera", 500.0);

System.out.println("=== ZenBank System ===");
        System.out.println("Account: " + account.accountHolder);
        System.out.println("Starting Balance: $" + account.balance);

account.deposit(150.0);
        account.withdraw(200.0);
        account.withdraw(600.0); // Should decline
    }
}

Output Console

Click "Run Code" to view the rendered output.

How it works: Encapsulates account logic, handles balance validation, and provides clean terminal output.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Build a student grade calculator

Given scores = {85, 90, 95}, calculate the average score.
If average >= 90, print "Grade: A". Otherwise print "Grade: B".

Sandbox Output

Click "Run & Check" to test your solution.

Finished reading and practicing?

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