Java generics - get class

Question

I got a list  programmed like this  public class MyList lt T gt   Is there any way to use the T variable to get the name of class  so I can  from within MyList  know if T is String  Socket  etc     EDIT  Nevermind  found the answer here

User · Answer

I m able to get the Class of the generic type this way   class MyList lt T gt      Class lt T gt  clazz    Class lt T gt   DAOUtil getTypeArguments MyList class  this getClass    get 0       You need two functions from this file  http   code google com p hibernate-generic-dao source browse trunk dao src main java com googlecode genericdao dao DAOUtil java  For more explanation  http   www artima com weblogs viewpost jsp thread 208860

User · Answer

Short answer  You can t   Long answer   Due to the way generics is implemented in Java  the generic type T is not kept at runtime  Still  you can use a private data member   public class Foo lt T gt         private Class lt T gt  type       public Foo Class lt T gt  type    this type   type         Usage example   Foo lt Integer gt  test   new Foo lt Integer gt  Integer class

User · Answer

You are seeing the result of Type Erasure  From that page        When a generic type is instantiated    the compiler translates those types by   a technique called type erasure     a   process where the compiler removes all   information related to type parameters   and type arguments within a class or   method  Type erasure enables Java   applications that use generics to   maintain binary compatibility with   Java libraries and applications that   were created before generics       For instance  Box lt String gt  is   translated to type Box  which is   called the raw type     a raw type is a   generic class or interface name   without any type arguments  This means   that you can t find out what type of   Object a generic class is using at   runtime    This also looks like this question which has a pretty good answer as well

User · Answer

I like the solution from  http   www nautsch net 2008 10 28 class-von-type-parameter-java-generics   public class Dada lt T gt         private Class lt T gt  typeOfT        SuppressWarnings  unchecked       public Dada             this typeOfT    Class lt T gt                     ParameterizedType getClass                    getGenericSuperclass                     getActualTypeArguments   0

User · Answer

I m not 100  sure if this works in all cases  needs at least Java 1 5    import java lang reflect Field  import java lang reflect ParameterizedType  import java lang reflect Type  import java util HashMap  import java util Map   public class Main        public class A                     public class B extends A                          public Map lt A  B gt  map   new HashMap lt Main A  Main B gt          public static void main String   args                  try                       Field field   Main class getField  map                           System out println  Field     field getName       is of type     field getType   getSimpleName                  Type genericType   field getGenericType                 if genericType instanceof ParameterizedType                                ParameterizedType type    ParameterizedType  genericType                                 Type   typeArguments   type getActualTypeArguments                     for Type typeArgument   typeArguments                                            Class lt   gt  classType     Class lt   gt  typeArgument                                         System out println  Field     field getName       has a parameterized type of     classType getSimpleName                                                       catch Exception e                        e printStackTrace                            This will output      Field map is of type Map   Field map has a parameterized type of A   Field map has a parameterized type of B

[java] Java generics - get class?

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