IntelliJ IDEA Guide — Setup, Shortcuts, Plugins, Refactoring, Debugging, Profiling

# Download IntelliJ IDEA (Ultimate or Community)
wget https://download.jetbrains.com/idea/ideaIU-2024.2.tar.gz

# Extract and run
tar xzf ideaIU-2024.2.tar.gz
cd idea-IU-242.*/bin
./idea.sh

# Create a new Java project
# File → New → Project → Java
# Choose JDK (File → Project Structure → SDK)

# Project SDK settings
# File → Project Structure (Ctrl+Alt+Shift+S)
# Project SDK: 21 (LTS)
# Language level: 21 (Preview)

# Install via Settings → Plugins (Ctrl+Alt+S)

# Essential plugins:
# 1. SonarLint — Real-time code quality checks
# 2. GitToolBox — Git status in editor, blame annotations
# 3. Key Promoter X — Shows shortcut for any action you click
# 4. Rainbow Brackets — Color-coded brackets
# 5. .env files — Environment file support
# 6. Spring Assistant — Spring Boot configuration completion
# 7. MyBatisX — MyBatis mapper navigation
# 8. Async Profiler — Built-in JVM profiling

// Before — hardcoded value
public class OrderService {
    private static final double TAX_RATE = 0.08;

    public double calculateTotal(double subtotal) {
        return subtotal + (subtotal * TAX_RATE);
    }
}

// Extract parameter refactoring (Ctrl+Alt+P)
public class OrderService {
    public double calculateTotal(double subtotal, double taxRate) {
        return subtotal + (subtotal * taxRate);
    }
}

// Rename refactoring (Shift+F6) — updates all references automatically
public class OrderService {
    public double calculateTotalWithTax(double subtotal, double taxRate) {
        return subtotal + (subtotal * taxRate);
    }
}

// Before
public void process() {
    List<Order> o = orderRepo.findAll();
    for (Order order : o) {
        // ...
    }
}

// After Shift+F6 on 'o' → rename to 'orders'
public void process() {
    List<Order> orders = orderRepo.findAll();
    for (Order order : orders) {
        // ...
    }
}

// Before — select the loop body, press Ctrl+Alt+M
public void processOrders(List<Order> orders) {
    for (Order order : orders) {
        if (order.getStatus() == OrderStatus.PENDING) {
            try {
                paymentService.process(order);
                order.setStatus(OrderStatus.PAID);
                notificationService.sendConfirmation(order);
            } catch (PaymentException e) {
                log.error("Payment failed for order {}", order.getId(), e);
                order.setStatus(OrderStatus.FAILED);
            }
        }
    }
}

// After extraction — new method with clear name
public void processOrders(List<Order> orders) {
    for (Order order : orders) {
        processSingleOrder(order);
    }
}

private void processSingleOrder(Order order) {
    if (order.getStatus() == OrderStatus.PENDING) {
        try {
            paymentService.process(order);
            order.setStatus(OrderStatus.PAID);
            notificationService.sendConfirmation(order);
        } catch (PaymentException e) {
            log.error("Payment failed for order {}", order.getId(), e);
            order.setStatus(OrderStatus.FAILED);
        }
    }
}

for (int i = 0; i < 10000; i++) {
    // Right-click breakpoint → set condition: i == 5678
    processItem(items[i]);
}

// At breakpoint, press Alt+F8 and type:
order.getTotal() > 1000
// Returns: true

// Modify a variable:
order.setStatus(OrderStatus.REFUNDED)

// Profile CPU — find hot methods
// Run → Profile → CPU Sample

// Profile allocations — find allocation hotspots
// Run → Profile → Allocation Sampling

// Example: Identify the slow method
public class ReportGenerator {
    // This method shows 80% CPU usage in profile
    public byte[] generatePdfReport(List<Transaction> transactions) {
        // Each PDF page regenerates styles — expensive
        for (Transaction t : transactions) {
            PdfPage page = new PdfPage();
            // ...
        }
    }

    // After optimization — reuse styles
    public byte[] generatePdfReportOptimized(List<Transaction> transactions) {
        PdfStyle style = new PdfStyle();  // Created once
        for (Transaction t : transactions) {
            PdfPage page = new PdfPage(style);  // Reuse style
            // ...
        }
    }
}

// LegacyOrderProcessor.java — Before refactoring
public class LegacyOrderProcessor {
    public void handle(Order o) throws Exception {
        // Validate
        if (o.getItems().isEmpty()) throw new Exception("No items");
        if (o.getTotal() <= 0) throw new Exception("Invalid total");

        // Process payment
        String chargeId = chargeCreditCard(o.getCardNumber(), o.getTotal());
        o.setChargeId(chargeId);

        // Send emails
        sendEmail(o.getCustomerEmail(), "Order Confirmed",
            "Your order #" + o.getId() + " has been confirmed.");

        // Update inventory
        for (Item item : o.getItems()) {
            item.setQuantity(item.getQuantity() - 1);
            inventoryRepo.save(item);
        }

        // Generate receipt
        String receipt = "Order #" + o.getId() + "\n";
        for (Item item : o.getItems()) {
            receipt += item.getName() + ": $" + item.getPrice() + "\n";
        }
        receipt += "Total: $" + o.getTotal();
        saveReceipt(o.getId(), receipt);
    }

    private String chargeCreditCard(String card, double amount) { return "ch_" + System.currentTimeMillis(); }
    private void sendEmail(String to, String subject, String body) { /* email logic */ }
    private void saveReceipt(long orderId, String receipt) { /* save logic */ }
}