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| <H2> |
| <FONT SIZE="-1"> |
| javax.inject</FONT> |
| <BR> |
| Annotation Type Inject</H2> |
| <HR> |
| <DL> |
| <DT><PRE><FONT SIZE="-1">@Target(value={METHOD,CONSTRUCTOR,FIELD}) |
| @Retention(value=RUNTIME) |
| @Documented |
| </FONT>public @interface <B>Inject</B></DL> |
| </PRE> |
| |
| <P> |
| Identifies injectable constructors, methods, and fields. Applies to static |
| as well as instance members. An injectable member may have any access |
| modifier (private, package-private, protected, public). Constructors are |
| injected first, followed by fields, and then methods. Fields and methods |
| in superclasses are injected before those in subclasses. Ordering of |
| injection among fields and among methods in the same class is not specified. |
| Which values are injected depends upon the injector implementation and its |
| configuration. |
| |
| <p>Injectable constructors are annotated with <code>@Inject</code> and accept |
| zero or more dependencies as arguments. <code>@Inject</code> can apply to at most |
| one constructor per class. |
| |
| <p><tt><blockquote style="padding-left: 2em; text-indent: -2em;">@Inject |
| <i>ConstructorModifiers<sub>opt</sub></i> |
| <i>SimpleTypeName</i>(<i>FormalParameterList<sub>opt</sub></i>) |
| <i>Throws<sub>opt</sub></i> |
| <i>ConstructorBody</i></blockquote></tt> |
| |
| <p><code>@Inject</code> is optional for public, no-argument constructors when no |
| other constructors are present. This enables injectors to invoke default |
| constructors. |
| |
| <p><tt><blockquote style="padding-left: 2em; text-indent: -2em;"> |
| @Inject<sub><i>opt</i></sub> |
| <i>Annotations<sub>opt</sub></i> |
| public |
| <i>SimpleTypeName</i>() |
| <i>Throws<sub>opt</sub></i> |
| <i>ConstructorBody</i></blockquote></tt> |
| |
| <p>Injectable fields: |
| <ul> |
| <li>are annotated with <code>@Inject</code>. |
| <li>are not final. |
| <li>may have any otherwise valid name.</li></ul> |
| |
| <p><tt><blockquote style="padding-left: 2em; text-indent: -2em;">@Inject |
| <i>FieldModifiers<sub>opt</sub></i> |
| <i>Type</i> |
| <i>VariableDeclarators</i>;</blockquote></tt> |
| |
| <p>Injectable methods: |
| <ul> |
| <li>are annotated with <code>@Inject</code>.</li> |
| <li>are not abstract.</li> |
| <li>do not declare type parameters of their own.</li> |
| <li>return <code>void</code>.</li> |
| <li>may have any otherwise valid name.</li> |
| <li>accept zero or more dependencies as arguments.</li></ul> |
| |
| <p><tt><blockquote style="padding-left: 2em; text-indent: -2em;">@Inject |
| <i>MethodModifiers<sub>opt</sub></i> |
| void |
| <i>Identifier</i>(<i>FormalParameterList<sub>opt</sub></i>) |
| <i>Throws<sub>opt</sub></i> |
| <i>MethodBody</i></blockquote></tt> |
| |
| <p>For example: |
| |
| <pre> |
| public class Car { |
| // Injectable constructor |
| @Inject public Car(Engine engine) { ... } |
| |
| // Injectable field |
| @Inject private Provider<Seat> seatProvider; |
| |
| // Injectable package-private method |
| @Inject void install(Windshield windshield, Trunk trunk) { ... } |
| }</pre> |
| |
| <p>A method annotated with <code>@Inject</code> that overrides another method |
| annotated with <code>@Inject</code> will only be injected once per injection |
| request per instance. A method with <i>no</i> <code>@Inject</code> annotation |
| that overrides a method annotated with <code>@Inject</code> will not be |
| injected. |
| |
| <p>Injection of members annotated with <code>@Inject</code> is required by |
| default. This behavior can be overridden by setting <A HREF="../../javax/inject/Inject.html#optional()"><CODE>optional</CODE></A> equal to <code>true</code>. |
| |
| <p>Detecting and resolving circular dependencies is left as an exercize for |
| the injector implementation. Circular dependencies between two constructors |
| is an obvious problem, but you can also have a circular dependency between |
| injectable fields or methods: |
| |
| <pre> |
| class A { |
| @Inject B b; |
| } |
| class B { |
| @Inject A a; |
| }</pre> |
| |
| <p>When constructing an instance of <code>A</code>, a naive injector |
| implementation might go into an infinite loop constructing an instance of |
| <code>B</code> to set on <code>A</code>, a second instance of <code>A</code> to set on |
| <code>B</code>, a second instance of <code>B</code> to set on the second instance of |
| <code>A</code>, and so on. |
| |
| <p>A conservative injector might detect the circular dependency at build |
| time and generate an error, at which point the programmer could break the |
| circular dependency by injecting <A HREF="../../javax/inject/Provider.html" title="interface in javax.inject"><CODE>Provider<A></CODE></A> or <code>Provider<B></code> instead of <code>A</code> or <code>B</code> respectively. Calling <A HREF="../../javax/inject/Provider.html#get()"><CODE>get()</CODE></A> on the provider directly from the constructor or |
| method it was injected into defeats the provider's ability to break up |
| circular dependencies. In the case of method or field injection, scoping |
| one of the dependencies (using <A HREF="../../javax/inject/Singleton.html" title="annotation in javax.inject">singleton scope</A>, for |
| example) may also enable a valid circular relationship. |
| <P> |
| |
| <P> |
| <DL> |
| <DT><B>See Also:</B><DD><A HREF="../../javax/inject/Qualifier.html" title="annotation in javax.inject"><CODE>@Qualifier</CODE></A>, |
| <A HREF="../../javax/inject/Provider.html" title="interface in javax.inject"><CODE>Provider</CODE></A></DL> |
| <HR> |
| |
| <P> |
| <!-- =========== ANNOTATION TYPE OPTIONAL MEMBER SUMMARY =========== --> |
| |
| <A NAME="annotation_type_optional_element_summary"><!-- --></A> |
| <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
| <TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"> |
| <TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"> |
| <B>Optional Element Summary</B></FONT></TH> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"> |
| <CODE> boolean</CODE></FONT></TD> |
| <TD><CODE><B><A HREF="../../javax/inject/Inject.html#optional()">optional</A></B></CODE> |
| |
| <BR> |
| Whether or not injection is optional.</TD> |
| </TR> |
| </TABLE> |
| |
| <P> |
| <A NAME="optional()"><!-- --></A><H3> |
| optional</H3> |
| <PRE> |
| public abstract boolean <B>optional</B></PRE> |
| <DL> |
| <DD>Whether or not injection is optional. If <code>true</code>, the injector's |
| behavior varies depending on the type of injection point: |
| |
| <p><ul> |
| <li><b>Constructors:</b> <i>Not allowed</i></li> |
| <li><b>Fields:</b> If a dependency matching the field can't |
| be found, the injector will not set the field.</li> |
| <li><b>Methods:</b> If a dependency matching a method parameter can't |
| be found, the injector will skip invoking the method entirely, even |
| if other arguments could be provided.</li> |
| </ul> |
| |
| <p>If an applicable dependency has been configured but the injector |
| encounters an error while resolving the dependency (a transitive |
| dependency could be missing, for example), the injector should generate |
| an error, not skip the injection. For example: |
| |
| <pre> |
| @Inject(optional=true) Gps gps;</pre> |
| |
| <p>If a Gps isn't available at all, the injector will simply not set the |
| <code>gps</code> field. If a Gps is available but an algorithm it depends |
| upon can't be found, the injector will generate an error. |
| <P> |
| <DD><DL> |
| </DL> |
| </DD> |
| <DD><DL> |
| </DL> |
| <DL> |
| <DT><B>Default:</B><DD>false</DD> |
| </DL> |
| </DL> |
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