Who creates and connects collaborators?

Goal & mental model verified

Inversion of control means the container constructs and connects collaborators. Dependency injection exposes what an object needs. Component scanning and @Bean methods are two ways to register bean definitions.

Worked example · illustrative, not executed synthesis

class QuoteService {
  private final PricingPort pricing;
  QuoteService(PricingPort pricing) { this.pricing = pricing; }
}
// Register QuoteService and a PricingPort implementation as beans.

Engineering decision synthesis

Use constructor injection for required collaborators. Use @Bean for third-party objects or explicit assembly; use qualifiers when multiple candidates represent meaningful alternatives.

Pitfall & diagnosis synthesis

Field injection hides required dependencies and complicates plain construction. Circular dependencies often signal tangled responsibilities; adding lazy references can conceal the design problem.

Improve & validate synthesis

Construct business services directly in unit tests. Inspect candidate ambiguity and configuration boundaries before widening component scans.