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Every annotation of the Covalent component model on one page. For each one, the table gives where it goes and what it means; follow the link for the full explanation. For a plain-language definition of the underlying concept, see the Glossary.

Component Structure

Annotation	Placed on	Meaning	Reference
`@Component`	interface	declares a component type (an empty tag interface)	Component Type
`@Implementation`	class; field of a composite	declares the implementation class of a component, or a sub-component field in a composite	Implementation, Composition
`@Item`	class; field	declares a component item class, or the field that holds it	Items
`@ComponentItem`	see Items	alternative to `@Item` on the field that aggregates an item	Items
`@ComposedComponent`	field	alternative to `@Implementation` on the field that owns a sub-component	Composition

Services, Parameters And Events

Annotation	Placed on	Meaning	Reference
`@Services`	interface; field	declares a services interface; on a field, same as `@UsedServices`	Services
`@UsedServices`	field	the component uses these services; the container injects the provider	Using Services
`@Parameters`	interface; field	declares a parameters interface; on a field, same as `@AccessedParameters`	Parameters
`@AccessedParameters`	field	the component accesses these parameters; the container injects them	Accessing Parameters
`@Events`	interface; field	declares an events interface; on a field, same as `@ProducedEvents`	Events
`@ProducedEvents`	field	the component produces these events	Producing Events
`@EventsSubscribe`	interface nested in an events interface	declares the subscribe interface of the events	Event Subscription
`@UsedEventsSubscribe`	field	the component subscribes manually, through a subscribe interface	Event Subscription
`@EventsFilter`	interface nested in an events interface	declares the filter interface of the events	Event Filters
`@Cloned`	events interface; event method; event method argument	clones the event arguments before delivery	Event Data Cloning

Lifecycle Callbacks

These annotations go on a method of the implementation, which must take no argument. Each one is equivalent to implementing the interface in the second column.

Annotation	Equivalent interface	Called	Reference
`@Initialization`	`Initializable`	once, when the component is initialized	Lifecycle Callbacks
`@Activation`	`Activable`	each time the component is activated	Lifecycle Callbacks
`@Passivation`	`Passivatable`	each time the component is passivated	Lifecycle Callbacks
`@Removal`	`Removable`	once, when the component is removed	Lifecycle Callbacks

ComponentLifecycleTransition declares the four callbacks in a single interface.

Infrastructure

Annotation	Placed on	Meaning	Reference
`@Internal`	class	marks a component of the container itself, as opposed to an application component; reserved to Covalent, refused on application components	Starting a Covalent Application

Where Each Annotation Lives

The component model annotations are in the package org.opales.covalent.container.component.annotations.
The lifecycle annotations and interfaces are in org.opales.covalent.container.lifecycle.
@Internal is in org.opales.covalent.container.component.internals.

Naming Conventions

Covalent recommends naming conventions for the elements it injects and calls. They are optional, unless structural rule verification is set to its strictest level; each kind can also be disabled individually. See Verification Level.

Element	Convention	Example
services interface	ends with `Services`	`PricingServices`
used services field	`use` + services interface name	`usePricingServices`
parameters interface	ends with `Parameters`	`PricingParameters`
accessed parameters field	`access` + parameters interface name	`accessPricingParameters`
events interface	ends with `Events`	`OrderEvents`
event method	`on` + past-tense verb	`onOrderPlaced`
produced events field	`produce` + events interface name	`produceOrderEvents`
events subscribe interface	ends with `Subscribe` (mandatory)	`OrderEventsSubscribe`
used events subscribe field	`use` + subscribe interface name	`useOrderEventsSubscribe`
filter interface	events interface name + `Filter` (mandatory for managed components)	`OrderEventsFilter`
filter method	event method name with `on` replaced by `filter` (mandatory)	`filterOrderPlaced`
subscribe and unsubscribe methods	prefixed with `subscribe` and `unsubscribe` (mandatory)	`subscribe(observer)`