Field Injection (Not Recommend)

You can also directly inject dependencies into fields using @Autowired. However, this approach is generally discouraged for a few reasons (it can make testing harder and can lead to circular dependencies that are harder to detect).

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
 
@Service
public class ReportService {
 
    @Autowired
    private DataFetcher dataFetcher;
 
    public String generateReport() {
        List<String> data = dataFetcher.fetchData();
        return "Report generated with " + data.size() + " items.";
    }
}
 
@Component
public class DataFetcher {
    public List<String> fetchData() {
        return List.of("Data 1", "Data 2", "Data 3");
    }
}

Here, Spring directly injects an instance of DataFetcher into the dataFetcher field of ReportService.