Explain the differences in the init() method when using Singleton and Prototype beans in the context of their lifecycle and initialization.

In the Spring Framework, the init() method (for example, annotated with @PostConstruct or specified in init-method) is called after the bean is created and configured.

For Singleton:

• The bean is created once at container startup or upon first access.
• The init() method is called once during the entire lifecycle of the application.
• Initialization occurs only once, saving resources.

For Prototype:

• Each request to the container creates a new bean instance.
• The init() method is called when each new instance is created.
• Initialization occurs multiple times, once for each object.

Thus, the difference is that init() for Singleton is called once, while for Prototype it is called each time a new instance is created, affecting performance and resource management.