Generic extending class AND implements interface

Question

This might sound like an odd question but how can on define a generic which has to extend a class AND to implement an interface? Im currently having a generic function with the following prototype:

public static <E extends Enum<E>> List<E> buildEnumList(Class<E> enumClass)

This works just as intented. My problem now is that I want to further restrict the passable classes to those which are enums and implement a specific interface Readable (not that in java.lang). Since a generic uses the same keyword extends to indicate that it should implement an interface, I dont see any way to get the following pseudo behaviour:

public static <E extends Enum<E> implements Readable> List<E> buildLexicographicalEnumList(Class<E> enumClass)

score 26 · Accepted Answer · answered Jul 26 '12 at 15:21

26

You can use & to indicate that E must also implement an interface:

public static <E extends Enum<E> & Readable> List<E> buildLexicographicalEnumList(Class<E> enumClass) {

answered Jul 26 '12 at 15:21

assylias

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A comma can also be used to separate them. – corsiKa Jul 26 '12 at 15:24
@corsiKa I thought so too but can't find it [in the JLS](http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.4). Although it does to compile. – assylias Jul 26 '12 at 15:25
Now I'm concerned they actually do two different things... :-( – corsiKa Jul 26 '12 at 15:27
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It defines a second/nth type parameter. – Ben Schulz Jul 26 '12 at 15:28
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@BenSchulz Indeed; A comma was my first try but it instead defined a second type parameter. This however works just fine – Sebastian Hoffmann Jul 26 '12 at 15:30
@corsiKa: Be carefull here: Comma does a different thing. The & is the correct way to specify what OP needs. – Mathias Bader Mar 02 '17 at 09:12

Generic extending class AND implements interface

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