TreeMap counting

import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.Random;
import java.util.stream.Stream;
import java.util.stream.IntStream;

class Main {
    public static void main(String[] args) {
        // Data generation
        Random rand = new Random();
        List<String> productNames = List.of("Mouse", "Keyboard", "Battery", "Laptop", "Pad Mouse", "Ethernet Cable")
            .stream()
            .flatMap(product -> Stream.generate(() -> product).limit(rand.nextInt(20 - 1) + 1))
            .toList();
            
        Map<String, Integer> productsByCategories = new TreeMap<>();
        // Categorization    
        for (String productName: productNames) {
            if (productsByCategories.containsKey(productName)) {
                var count = productsByCategories.get(productName) + 1;
                productsByCategories.put(productName, count);
            } else {
                productsByCategories.put(productName, 1);
            }
        }
        
        // Print output
        System.out.println("Product names: " + productNames);
        for (Map.Entry<String, Integer> productByCategory : productsByCategories.entrySet()) {
            System.out.println("Product: " + productByCategory.getKey() + " - " + productByCategory.getValue());
        }
        
        
    }
}