Classes and Objects in Java

package io.thecodeforge.java.oop;

import java.util.UUID;

/**
 * Production-grade BankAccount implementation emphasizing encapsulation.
 */
public class BankAccount {

    private final String accountId;
    private String owner;
    private double balance;

    // Constructor: Essential for ensuring an object starts in a valid state
    public BankAccount(String owner, double initialBalance) {
        if (initialBalance < 0) {
            throw new IllegalArgumentException("Initial balance cannot be negative");
        }
        this.accountId = UUID.randomUUID().toString();
        this.owner = owner;
        this.balance = initialBalance;
    }

    public void deposit(double amount) {
        if (amount <= 0) throw new IllegalArgumentException("Deposit must be positive");
        this.balance += amount;
    }

    public boolean withdraw(double amount) {
        if (amount > this.balance) return false;
        this.balance -= amount;
        return true;
    }

    // Standard Getters
    public double getBalance() { return this.balance; }
    public String getOwner()   { return this.owner; }
    public String getAccountId() { return this.accountId; }

    @Override
    public String toString() {
        return String.format("BankAccount[ID=%s, owner=%s, balance=%.2f]",
                accountId, owner, balance);
    }
}

package io.thecodeforge.java.oop;

public class BankAccountDemo {
    public static void main(String[] args) {
        // Each 'new' call creates a unique identity in memory
        BankAccount accountA = new BankAccount("Senior Dev", 5000.00);
        BankAccount accountB = new BankAccount("Junior Dev", 1000.00);

        accountA.deposit(500.00);

        System.out.println(accountA);
        System.out.println(accountB);

        // Reference comparison vs Identity
        System.out.println("Different objects: " + (accountA != accountB));
    }
}

package io.thecodeforge.java.oop;

public class Product {
    private String sku;
    private double price;
    private int stock;

    // Primary Constructor
    public Product(String sku, double price, int stock) {
        this.sku = sku;
        this.price = price;
        this.stock = stock;
    }

    // Overloaded Constructor: Defaults stock to zero
    public Product(String sku, double price) {
        this(sku, price, 0); 
    }

    // Overloaded Constructor: Default/Placeholder values
    public Product() {
        this("PENDING-SKU", 0.0, 0);
    }

    @Override
    public String toString() {
        return String.format("Product[%s] - $%.2f (In Stock: %d)", sku, price, stock);
    }
}

package io.thecodeforge.java.oop;

public class Counter {
    private int count = 0;
    private final String label;

    public Counter(String label) {
        this.label = label; // 'this.label' refers to field; 'label' refers to parameter
    }

    // Method Chaining: Return 'this' to allow consecutive calls
    public Counter increment() {
        this.count++;
        return this;
    }

    public void display() {
        System.out.println(this.label + " status: " + this.count);
    }

    public static void main(String[] args) {
        new Counter("System-Metrics")
            .increment()
            .increment()
            .display();
    }
}