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| <title>Adding new interfaces</title> |
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| <H2> Adding new interfaces</H2> |
| New types of objects can be passed into a part's constructor by registering them |
| with the the <span style="font-style: italic;">org.eclipse.core.component.types</span> |
| extension point. At this point, we should introduce the term <span |
| style="font-style: italic;">component</span>. A component is any sort of object |
| that is created from an extension point by injecting arguments into its constructor. |
| New-style parts are one sort of component, but there are other types of components |
| as well.<br> |
| <br> |
| The following example shows a sample types extension. This example specifies that |
| the INameable interface should be available from a part's site.<br> |
| <br> |
| <div style="margin-left: 40px;"><code><extension</code><br> |
| <code> point="org.eclipse.core.component.types"></code><br> |
| <code> <component<br> |
| </code><code> initializer="org.eclipse.ui.part.SiteInitializer"</code><br> |
| <code> interface="org.eclipse.ui.part.services.INameable"<br> |
| </code><code> implementation="org.eclipse.ui.internal.part.services.NullNameableService"</code><br> |
| <code> singleton="true"</code><br> |
| <code> /></code><br> |
| <code></extension></code><br> |
| </div> |
| <p>The <span style="font-style: italic;">initializer</span> attribute indicates |
| where the interface will be used. For example, the string "org.eclipse.ui.part.SiteInitializer" |
| means that the interface is used on a part's site. We could have also used "org.eclipse.ui.part.PartInitializer" |
| if the interface was intended for parts themselves to implement. <br> |
| <br> |
| The <span style="font-style: italic;">interface</span> attribute is the name |
| of the interface. This must exactly match the type that the component will receive |
| in its constructor. If we create an extension that supplies Strings and a component |
| asks for an Object, it will not use our extension even though it would have |
| been a compatible type. <br> |
| <br> |
| The <span style="font-style: italic;">implementation</span> attribute identifies |
| the default implementation of the interface. It either points to a component |
| class that implements the interface or a ComponentFactory that can create them, |
| for additional information, see the ComponentFactory section . This implementation |
| is used to satisfy a dependency whenever a component requests this interface |
| and it can't be found in its parent context. All interfaces must supply a default |
| implementation. This means that a correctly written component will always work |
| in a given scope, regardless of how many dependencies are supplied by its parent |
| context. The implementation cannot override or extend the interface attribute |
| by implementing additional interfaces. Other components can depend on this component |
| through its registered interface, but cannot depend on the implementation class |
| directly. <br> |
| <br> |
| The <span style="font-style: italic;">singleton</span> attribute indicates whether |
| the default implementation is a singleton. If true, then a single instance will |
| be created and shared between every other component that needs it. If false, |
| then a new instance will be created for each container that needs it. For example, |
| in the case of parts, singleton=:"false" would mean that one instance will be |
| created for every part.<br> |
| </p> |
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