[jboss-user] [JBoss Seam] - does seam ignore generics in lists?
hi all,
following _very_ strange behaviour:
in a SFSB i have 3 lists defined as follows:
| [...]
| @Out (required=false)
| private List<TimetableItem> bscLectures;
| @Out (required=false)
| private List<TimetableItem> bscPracticals;
| private List<TimetableItem> selectedBscLectures;
| [...]
|
in a .xhtml file:
| <h:selectManyCheckbox id="lectureBscList"
| value="#{timetable.selectedBscLectures}"
layout="pageDirection">
| <s:selectItems value="#{timetable.bscLectures}"
var="lecture"
| label="#{lecture.title} (#{lecture.type}): #{lecture.times}" />
| </h:selectManyCheckbox>
| [...]
| <h:dataTable id="bscPracticalList" var="bscPr"
| value="#{timetable.bscPracticals}"
| rendered="#{not empty timetable.bscPracticals}">
| <h:column>
| #{bscPr.title}
| </h:column>
| <h:column>
| <h:selectOneMenu value="#{bscPr.selected}">
| <s:selectItems value="#{bscPr.times}" var="n"
| label="#{n.toShortString()}"
| noSelectionLabel="Please select..."/>
| </h:selectOneMenu>
| </h:column>
| </h:dataTable>
|
TimetableItem is not an Entity Bean, it's a helper class i've mashed together,
with the following fields:
| private String title;
| private String type;
| private List<TimetableItemTime> times;
| private Object selected; // this should be a TimetableItem as well
|
i realised that i've got some problems somewhere when i tried the following:
| for (TimetableItem t : this.selectedBscLectures)
| System.out.println(t.toString())); // changed for ease of reading
|
and it was giving me ClassCastExceptions. The SelectOneMenu's were doing the same
thing on TimetableItem.selected, which is why i changed that to an Object. After
investigating further, i found out that my List selectedBscLectures is actually populated
with Strings.
2 questions:
1.) why strings?
2.) why isn't the JVM screaming loudly about violations of the Generics?
[i may have an answer for 2.):]
constructs like this aren't caught by the java compiler, but do cause
ClassCastExceptions at runtime.
| import java.util.*;
|
| public class Test {
| public static void main(String args[]) {
| ArrayList<Integer> integerList = new ArrayList<Integer>();
| integerList.add(1);
| Object o = new String("Simon!");
| integerList.add((Integer)o);
| }
| }
|
now the interesting question is, where are the ClassCastExceptions which should be
happening going? they're not in my server log...
[possible answer to 1.): i'm assuming because my beans aren't @Entity's, they
have no @Id, which means that the JVM is using the toString() to identify them (the value
of checkbox is a string representation of the object), and passing this into the Lists.
but how do i avoid this?]
regards,
sb
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