Changes between Version 2 and Version 3 of ExampleUsingOwnConceteTypes

Timestamp:

10/06/06 17:09:28 (19 years ago)

Author:

lauer

Comment:

--

ExampleUsingOwnConceteTypes

@@ -1 +1 @@
 == Using own concete types ==
 
-[|Special case: Using own types in Collections and Maps.] Java's type erasure in action!
+[http://delight.opendfki.de/wiki/ExampleUsingOwnConceteTypes#UsingowntypesinCollectionsandMaps Special case: Using own types in Collections and Maps.] Java's type erasure in action!
 
 === Server side ===
 
+We want to use the type {{{Param}}} in our API. Normally, this will cause an error message. See how we can make this type
+XML-RPC compliant with only a few lines of code:
 
 {{{
@@ -16 +18 @@
 public class Impl implements Api
 {
-    public Param returnParam() { return new ParamImpl( ... ); }
+    public Param returnParam() { return createParam( ... ); }
     
-    void passAsParameter( Param p ) {}
+    void passAsParameter( Param p ) { doSomethingWith( p ); }
 }
-
 }}}
 
@@ -69 +70 @@
 == Using own types in Collections and Maps ==
 
+When using generics in the API methods, java runs a so called type erasure on all generic types, reducing a Collection<Param> to a simple Collection. 
+The runtime system cannot determine the content type of this collection unless the user places an extra hint using the @Contains annotation.
+
+{{{
+// DOES NOT WORK: Map<String,Param> will be reduced to Map, Collection<Param> will be reduced to Collection
+public interface Api
+{
+    Map<String,Param> returnMyParamInMap();
+    
+    void passManyParams( Collection<Param> params );
+}
+}}}
+
+Place a @Contains in front of the method to annotate a return type. Place it before a formal parameter
+to annotate method parameters.
+{{{
+// WORKS!
+public interface Api
+{
+    @Contains(Param.class)
+    Map<String,Param> returnMyParamInMap();
+    
+    void passManyParams( @Contains(Param.class) 
+                         Collection<Param> params );
+}
+}}}
+
+== Client Side ==
+Now remote clients can also use Collections and Maps containing own types:
+{{{
+Api remote_api = XmlRpc.createClient( Api.class, "handlerId", host, port );
+
+Map<String,Param> map = remote_api.returnMyParamInMap();
+for( Param p : map.values() )
+{
+  ...
+}
+
+remote_api.passManyParams( Collections.asList( new Param[]{new Param()} ) );
+...
+}}}