What are component dependencies in Dagger?

Component dependencies in Dagger 2 are relationships between components that allow one component to provide objects to another. This is achieved through the dependencies attribute in the @Component annotation.

When using dependencies:

• The child component gains access to objects provided by the parent component.
• The parent component does not have access to objects provided by the child component.

Example:

// Parent component
@Component(modules = ParentModule.class)
interface ParentComponent {
    SomeObject provideSomeObject();
}

// Child component depending on parent
@Component(dependencies = ParentComponent.class, modules = ChildModule.class)
interface ChildComponent {
    void inject(SomeActivity activity); // Can use SomeObject from ParentComponent
}

Here, ChildComponent depends on ParentComponent. This means ChildComponent can use objects exported by ParentComponent (in this case, SomeObject via provideSomeObject() method). For the child component to use parent objects, these objects must be explicitly provided in the parent component.

This differs from subcomponents, where the child subcomponent automatically has access to all objects of the parent component, and vice versa. Dependency relationships are more explicit and help control access to individual objects across your dependency graph.