Bean lifecycle ke MAIN steps: 1) INSTANTIATION — Spring constructor call karके object banata hai. 2) POPULATE PROPERTIES — dependencies inject hoti hain. 3) INITIALIZATION — @PostConstruct method (ya InitializingBean.afterPropertiesSet()) call hota hai, agar define ho. 4) READY TO USE — bean ab application mein use ke liye available hai. 5) DESTRUCTION — container shutdown hone par, @PreDestroy method (ya DisposableBean.destroy()) call hota hai.

@PostConstruct useful hai jab bean ko dependencies mil jaने ke BAAD kuch setup karna ho (jaise cache warm-up, connection pool initialize karna) — constructor mein ye karna risky hai kyunki dependencies abhi fully inject nahi hui hoti.

@Service
public class CacheService {
    @Autowired
    private DataRepository repository;

    @PostConstruct
    public void init() {
        // Dependencies inject ho chuki hain, ab safe hai:
        System.out.println("Cache warming up...");
        loadInitialData();
    }

    @PreDestroy
    public void cleanup() {
        System.out.println("Closing connections...");
        // resource cleanup, jaise DB connections close karna
    }
}