Java : How to get type of List [duplicate]



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0
















This question already has an answer here:



  • Get generic type of class at runtime

    23 answers



I'm working on reflection in java.
I know this is a common question and there are a lot of articles about it but I'm a bit confused and can't seem to find the right solution for what I'm trying to achieve.



I have :



public class ClassA 
private List<?> myList;
// getters, setters



"myList" will contain a list of objects (DTOs) :



List<?> myList; // could be List<DTO1> or List<DTO2> ...


I'm trying to get the type of the list from another class like this :



public class ClassB 
public void myMethod()
// get type of ClassA.getMyList()




I can only get "ArrayList" when I try using stuff like getClass(), getType()...
Trying to get the class of an element in the list results in "LinkedHashMap".



I really want to achieve this by using a wildcard type for the list.



So is there a way I can get the type of myList with minimal code ?




EDIT :



Thank you all for your answers.



Just one thing : myList contains elements of type LinkedHashMap, this wasn't very clear on my post.



It seems this really can't be done. Each LinkedHashMap represents an object but you can't know which one. They are just a list of keys + values.










share|improve this question















marked as duplicate by Matthieu Brucher, user6910411, Max Vollmer, KevinO, Zephyr Nov 19 '18 at 3:47


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.


















  • did you try ClassA.getMyList().get(0).getClass() ??

    – Paplusc
    Nov 16 '18 at 11:25







  • 4





    You can't. Type erasure. ClassA should probably be generic. class ClassA<T> private List<T> myList;

    – Michael
    Nov 16 '18 at 11:27












  • @Michael but if you do a getClass() from any element in the List you will get it, won't you?

    – Paplusc
    Nov 16 '18 at 11:34






  • 2





    @Paplusc What if it's a List<Object>? The first element could be a string, the second could be an integer, the third could be a HashMap. Getting the class of the first element doesn't tell you much.

    – Michael
    Nov 16 '18 at 11:35












  • @Michal True that, i didn't think in that possibility.

    – Paplusc
    Nov 16 '18 at 11:46

















0
















This question already has an answer here:



  • Get generic type of class at runtime

    23 answers



I'm working on reflection in java.
I know this is a common question and there are a lot of articles about it but I'm a bit confused and can't seem to find the right solution for what I'm trying to achieve.



I have :



public class ClassA 
private List<?> myList;
// getters, setters



"myList" will contain a list of objects (DTOs) :



List<?> myList; // could be List<DTO1> or List<DTO2> ...


I'm trying to get the type of the list from another class like this :



public class ClassB 
public void myMethod()
// get type of ClassA.getMyList()




I can only get "ArrayList" when I try using stuff like getClass(), getType()...
Trying to get the class of an element in the list results in "LinkedHashMap".



I really want to achieve this by using a wildcard type for the list.



So is there a way I can get the type of myList with minimal code ?




EDIT :



Thank you all for your answers.



Just one thing : myList contains elements of type LinkedHashMap, this wasn't very clear on my post.



It seems this really can't be done. Each LinkedHashMap represents an object but you can't know which one. They are just a list of keys + values.










share|improve this question















marked as duplicate by Matthieu Brucher, user6910411, Max Vollmer, KevinO, Zephyr Nov 19 '18 at 3:47


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.


















  • did you try ClassA.getMyList().get(0).getClass() ??

    – Paplusc
    Nov 16 '18 at 11:25







  • 4





    You can't. Type erasure. ClassA should probably be generic. class ClassA<T> private List<T> myList;

    – Michael
    Nov 16 '18 at 11:27












  • @Michael but if you do a getClass() from any element in the List you will get it, won't you?

    – Paplusc
    Nov 16 '18 at 11:34






  • 2





    @Paplusc What if it's a List<Object>? The first element could be a string, the second could be an integer, the third could be a HashMap. Getting the class of the first element doesn't tell you much.

    – Michael
    Nov 16 '18 at 11:35












  • @Michal True that, i didn't think in that possibility.

    – Paplusc
    Nov 16 '18 at 11:46













0












0








0









This question already has an answer here:



  • Get generic type of class at runtime

    23 answers



I'm working on reflection in java.
I know this is a common question and there are a lot of articles about it but I'm a bit confused and can't seem to find the right solution for what I'm trying to achieve.



I have :



public class ClassA 
private List<?> myList;
// getters, setters



"myList" will contain a list of objects (DTOs) :



List<?> myList; // could be List<DTO1> or List<DTO2> ...


I'm trying to get the type of the list from another class like this :



public class ClassB 
public void myMethod()
// get type of ClassA.getMyList()




I can only get "ArrayList" when I try using stuff like getClass(), getType()...
Trying to get the class of an element in the list results in "LinkedHashMap".



I really want to achieve this by using a wildcard type for the list.



So is there a way I can get the type of myList with minimal code ?




EDIT :



Thank you all for your answers.



Just one thing : myList contains elements of type LinkedHashMap, this wasn't very clear on my post.



It seems this really can't be done. Each LinkedHashMap represents an object but you can't know which one. They are just a list of keys + values.










share|improve this question

















This question already has an answer here:



  • Get generic type of class at runtime

    23 answers



I'm working on reflection in java.
I know this is a common question and there are a lot of articles about it but I'm a bit confused and can't seem to find the right solution for what I'm trying to achieve.



I have :



public class ClassA 
private List<?> myList;
// getters, setters



"myList" will contain a list of objects (DTOs) :



List<?> myList; // could be List<DTO1> or List<DTO2> ...


I'm trying to get the type of the list from another class like this :



public class ClassB 
public void myMethod()
// get type of ClassA.getMyList()




I can only get "ArrayList" when I try using stuff like getClass(), getType()...
Trying to get the class of an element in the list results in "LinkedHashMap".



I really want to achieve this by using a wildcard type for the list.



So is there a way I can get the type of myList with minimal code ?




EDIT :



Thank you all for your answers.



Just one thing : myList contains elements of type LinkedHashMap, this wasn't very clear on my post.



It seems this really can't be done. Each LinkedHashMap represents an object but you can't know which one. They are just a list of keys + values.





This question already has an answer here:



  • Get generic type of class at runtime

    23 answers







java generics reflection wildcard






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 16 '18 at 13:05







Mr.G

















asked Nov 16 '18 at 11:24









Mr.GMr.G

33




33




marked as duplicate by Matthieu Brucher, user6910411, Max Vollmer, KevinO, Zephyr Nov 19 '18 at 3:47


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.









marked as duplicate by Matthieu Brucher, user6910411, Max Vollmer, KevinO, Zephyr Nov 19 '18 at 3:47


This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.














  • did you try ClassA.getMyList().get(0).getClass() ??

    – Paplusc
    Nov 16 '18 at 11:25







  • 4





    You can't. Type erasure. ClassA should probably be generic. class ClassA<T> private List<T> myList;

    – Michael
    Nov 16 '18 at 11:27












  • @Michael but if you do a getClass() from any element in the List you will get it, won't you?

    – Paplusc
    Nov 16 '18 at 11:34






  • 2





    @Paplusc What if it's a List<Object>? The first element could be a string, the second could be an integer, the third could be a HashMap. Getting the class of the first element doesn't tell you much.

    – Michael
    Nov 16 '18 at 11:35












  • @Michal True that, i didn't think in that possibility.

    – Paplusc
    Nov 16 '18 at 11:46

















  • did you try ClassA.getMyList().get(0).getClass() ??

    – Paplusc
    Nov 16 '18 at 11:25







  • 4





    You can't. Type erasure. ClassA should probably be generic. class ClassA<T> private List<T> myList;

    – Michael
    Nov 16 '18 at 11:27












  • @Michael but if you do a getClass() from any element in the List you will get it, won't you?

    – Paplusc
    Nov 16 '18 at 11:34






  • 2





    @Paplusc What if it's a List<Object>? The first element could be a string, the second could be an integer, the third could be a HashMap. Getting the class of the first element doesn't tell you much.

    – Michael
    Nov 16 '18 at 11:35












  • @Michal True that, i didn't think in that possibility.

    – Paplusc
    Nov 16 '18 at 11:46
















did you try ClassA.getMyList().get(0).getClass() ??

– Paplusc
Nov 16 '18 at 11:25






did you try ClassA.getMyList().get(0).getClass() ??

– Paplusc
Nov 16 '18 at 11:25





4




4





You can't. Type erasure. ClassA should probably be generic. class ClassA<T> private List<T> myList;

– Michael
Nov 16 '18 at 11:27






You can't. Type erasure. ClassA should probably be generic. class ClassA<T> private List<T> myList;

– Michael
Nov 16 '18 at 11:27














@Michael but if you do a getClass() from any element in the List you will get it, won't you?

– Paplusc
Nov 16 '18 at 11:34





@Michael but if you do a getClass() from any element in the List you will get it, won't you?

– Paplusc
Nov 16 '18 at 11:34




2




2





@Paplusc What if it's a List<Object>? The first element could be a string, the second could be an integer, the third could be a HashMap. Getting the class of the first element doesn't tell you much.

– Michael
Nov 16 '18 at 11:35






@Paplusc What if it's a List<Object>? The first element could be a string, the second could be an integer, the third could be a HashMap. Getting the class of the first element doesn't tell you much.

– Michael
Nov 16 '18 at 11:35














@Michal True that, i didn't think in that possibility.

– Paplusc
Nov 16 '18 at 11:46





@Michal True that, i didn't think in that possibility.

– Paplusc
Nov 16 '18 at 11:46












2 Answers
2






active

oldest

votes


















0














You can try this. I dont know it will solve your purpose or not but may be help.



 import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;

public class App
public static void main(String args)
ClassA classA = new ClassA();

List<String> strs = new ArrayList<>();

strs.add("A");
strs.add("B");

classA.setRepos(strs);

String typeOfList = classA.getRepos().getClass().getTypeName();
System.out.println("Type of variable in classA : "+typeOfList);

String typeOfListData = classA.getRepos().get(0).getClass().getTypeName();
System.out.println("Type of data inside the list : "+typeOfListData);

for (String s: (List<String>)classA.getRepos())

System.out.println(s);






ClassA will be like this



import java.util.List;

public class ClassA
private List<?> repos;

public List<?> getRepos()
return repos;


public void setRepos(List<?> repos)
this.repos = repos;




Output will be like this :



Type of variable in classA : java.util.ArrayList
Type of data inside the list : java.lang.String
A
B





share|improve this answer
































    0















    Duplicates:
    Get generic type of class at runtime




    That example demonstrates that any list can hold objects of any classes:



     List<String> stringList = new ArrayList<>();
    List list = stringList;
    list.add(new Object());
    for (String s : stringList)
    System.out.println(s);



    Only thing that you can do - is to test classes of elements if the list contains any.






    share|improve this answer





























      2 Answers
      2






      active

      oldest

      votes








      2 Answers
      2






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      0














      You can try this. I dont know it will solve your purpose or not but may be help.



       import java.lang.reflect.Type;
      import java.util.ArrayList;
      import java.util.List;

      public class App
      public static void main(String args)
      ClassA classA = new ClassA();

      List<String> strs = new ArrayList<>();

      strs.add("A");
      strs.add("B");

      classA.setRepos(strs);

      String typeOfList = classA.getRepos().getClass().getTypeName();
      System.out.println("Type of variable in classA : "+typeOfList);

      String typeOfListData = classA.getRepos().get(0).getClass().getTypeName();
      System.out.println("Type of data inside the list : "+typeOfListData);

      for (String s: (List<String>)classA.getRepos())

      System.out.println(s);






      ClassA will be like this



      import java.util.List;

      public class ClassA
      private List<?> repos;

      public List<?> getRepos()
      return repos;


      public void setRepos(List<?> repos)
      this.repos = repos;




      Output will be like this :



      Type of variable in classA : java.util.ArrayList
      Type of data inside the list : java.lang.String
      A
      B





      share|improve this answer





























        0














        You can try this. I dont know it will solve your purpose or not but may be help.



         import java.lang.reflect.Type;
        import java.util.ArrayList;
        import java.util.List;

        public class App
        public static void main(String args)
        ClassA classA = new ClassA();

        List<String> strs = new ArrayList<>();

        strs.add("A");
        strs.add("B");

        classA.setRepos(strs);

        String typeOfList = classA.getRepos().getClass().getTypeName();
        System.out.println("Type of variable in classA : "+typeOfList);

        String typeOfListData = classA.getRepos().get(0).getClass().getTypeName();
        System.out.println("Type of data inside the list : "+typeOfListData);

        for (String s: (List<String>)classA.getRepos())

        System.out.println(s);






        ClassA will be like this



        import java.util.List;

        public class ClassA
        private List<?> repos;

        public List<?> getRepos()
        return repos;


        public void setRepos(List<?> repos)
        this.repos = repos;




        Output will be like this :



        Type of variable in classA : java.util.ArrayList
        Type of data inside the list : java.lang.String
        A
        B





        share|improve this answer



























          0












          0








          0







          You can try this. I dont know it will solve your purpose or not but may be help.



           import java.lang.reflect.Type;
          import java.util.ArrayList;
          import java.util.List;

          public class App
          public static void main(String args)
          ClassA classA = new ClassA();

          List<String> strs = new ArrayList<>();

          strs.add("A");
          strs.add("B");

          classA.setRepos(strs);

          String typeOfList = classA.getRepos().getClass().getTypeName();
          System.out.println("Type of variable in classA : "+typeOfList);

          String typeOfListData = classA.getRepos().get(0).getClass().getTypeName();
          System.out.println("Type of data inside the list : "+typeOfListData);

          for (String s: (List<String>)classA.getRepos())

          System.out.println(s);






          ClassA will be like this



          import java.util.List;

          public class ClassA
          private List<?> repos;

          public List<?> getRepos()
          return repos;


          public void setRepos(List<?> repos)
          this.repos = repos;




          Output will be like this :



          Type of variable in classA : java.util.ArrayList
          Type of data inside the list : java.lang.String
          A
          B





          share|improve this answer















          You can try this. I dont know it will solve your purpose or not but may be help.



           import java.lang.reflect.Type;
          import java.util.ArrayList;
          import java.util.List;

          public class App
          public static void main(String args)
          ClassA classA = new ClassA();

          List<String> strs = new ArrayList<>();

          strs.add("A");
          strs.add("B");

          classA.setRepos(strs);

          String typeOfList = classA.getRepos().getClass().getTypeName();
          System.out.println("Type of variable in classA : "+typeOfList);

          String typeOfListData = classA.getRepos().get(0).getClass().getTypeName();
          System.out.println("Type of data inside the list : "+typeOfListData);

          for (String s: (List<String>)classA.getRepos())

          System.out.println(s);






          ClassA will be like this



          import java.util.List;

          public class ClassA
          private List<?> repos;

          public List<?> getRepos()
          return repos;


          public void setRepos(List<?> repos)
          this.repos = repos;




          Output will be like this :



          Type of variable in classA : java.util.ArrayList
          Type of data inside the list : java.lang.String
          A
          B






          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Nov 16 '18 at 11:39

























          answered Nov 16 '18 at 11:34









          flopcoderflopcoder

          777513




          777513























              0















              Duplicates:
              Get generic type of class at runtime




              That example demonstrates that any list can hold objects of any classes:



               List<String> stringList = new ArrayList<>();
              List list = stringList;
              list.add(new Object());
              for (String s : stringList)
              System.out.println(s);



              Only thing that you can do - is to test classes of elements if the list contains any.






              share|improve this answer



























                0















                Duplicates:
                Get generic type of class at runtime




                That example demonstrates that any list can hold objects of any classes:



                 List<String> stringList = new ArrayList<>();
                List list = stringList;
                list.add(new Object());
                for (String s : stringList)
                System.out.println(s);



                Only thing that you can do - is to test classes of elements if the list contains any.






                share|improve this answer

























                  0












                  0








                  0








                  Duplicates:
                  Get generic type of class at runtime




                  That example demonstrates that any list can hold objects of any classes:



                   List<String> stringList = new ArrayList<>();
                  List list = stringList;
                  list.add(new Object());
                  for (String s : stringList)
                  System.out.println(s);



                  Only thing that you can do - is to test classes of elements if the list contains any.






                  share|improve this answer














                  Duplicates:
                  Get generic type of class at runtime




                  That example demonstrates that any list can hold objects of any classes:



                   List<String> stringList = new ArrayList<>();
                  List list = stringList;
                  list.add(new Object());
                  for (String s : stringList)
                  System.out.println(s);



                  Only thing that you can do - is to test classes of elements if the list contains any.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Nov 16 '18 at 11:47









                  Aleksandr SemyannikovAleksandr Semyannikov

                  593217




                  593217













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