@Bean inside class with @Configuration and without it

The difference is that with @Configuration you can call one @Bean method from another and get a fully initialized instance, as follows:

public class Foo {
    @Value("Hello, world!")
    public String value;
}

@Configuration
public class Config {
    @Bean
    public Foo createFoo() {
        Foo foo = new Foo();
        System.out.println(foo.value); // Prints null - foo not initialized yet
        return foo;
    }

    @Bean
    public Bar createBar() {
        Foo foo = createFoo();
        System.out.println(foo.value); // Prints Hello, world! - foo have been initialized by the interceptor
        return new Bar(foo);
    }
}

@Bean [instance method] inside @Component - One method with @Bean instance call other method @Bean instance , then it would be simple java semantics call i.e. Object won't returned by Spring container , It would be normal return from java instance factory method,because Component class don't extends CGLIB.

@Bean [instance method] inside @Configuration - In this case , spring container would be returning reference to exisiting object. It won't be normal java sematic call.

@Bean on static method inside Configuration & Component Class - In this case , @Bean method would never be intercepted by the container neither in Configuration class nor in Component Sterotype class.