When should you prefer custom collectors and when should you avoid it?

When adding custom collectors to your Java Stream API usage, it’s important to weigh the benefits against potential downsides. Custom collectors can be very powerful, enabling you to create tailored collection mechanisms suiting your specific needs. However, there are scenarios where using them may not be the best choice.

When to Prefer Custom Collectors

• Complex Collection Needs: If you have complex data gathering requirements, custom collectors can help you efficiently process and accumulate results.
• Performance Optimization: In some cases, a custom collector can provide better performance than existing collectors, especially when handling large datasets.
• Enhanced Readability: Custom collectors can encapsulate business logic, making your stream operations more readable and maintainable.

When to Avoid Custom Collectors

• Simple Use Cases: If your collection needs are straightforward, it’s usually better to use built-in collectors (e.g., Collectors.toList(), Collectors.toSet()).
• Increased Complexity: Adding custom collectors can add unnecessary complexity to your codebase, especially if not documented properly.
• Overhead: If performance is not a concern, the custom implementation could add more overhead than using standard collectors.

Example of a Custom Collector

import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.List;
import java.util.Map;

public class CustomCollectorExample {
    public static void main(String[] args) {
        List names = List.of("Alice", "Bob", "Charlie", "Diana");

        // Custom collector to group names by their length
        Collector>> groupingByLength = Collectors.groupingBy(String::length);
        
        Map> groupedNames = names.stream().collect(groupingByLength);
        
        System.out.println(groupedNames);
    }
}