Groups > comp.lang.java.programmer > #35484

Re: Java 8 Lambda with generic types

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From	Steven Simpson <ss@my.domain.invalid>
Newsgroups	comp.lang.java.programmer
Subject	Re: Java 8 Lambda with generic types
Date	Sun, 28 Aug 2016 08:19:26 +0100
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On 28/08/16 07:50, Stone Zhong wrote:

> However, if I have
>          checkToy(() -> {
>              return Arrays.<Integer>asList(10);
>          });
>
> I got compiling error: "List<Integer> cannot be converted to List<Object>", it seems compiler tried to create a instance of Toy<Object> instead of Toy<Integer> based on the lambda. Is there a wait to tell the compiler it is Toy<Integer> explicitly with the lambda expression?

Do you need the <Integer> qualification on asList?  It seems to work 
without:

import java.util.*;
import java.util.function.*;

public class Funk {
     interface Toy<E> {
         List<E> get();
     }
     
     static void checkToy(Toy<?> toy) { }

     public void test() {
         checkToy(new Toy<Integer>() {
                 @Override
                 public List<Integer> get() {
                     return Arrays.asList(10);
                 }
             });

         checkToy(() -> Arrays.asList(10));
         checkToy(() -> { return Arrays.asList(10); });
     }
}


-- 
ss at comp dot lancs dot ac dot uk

Thread

Java 8 Lambda with generic types Stone Zhong <stone.zhong@gmail.com> - 2016-08-27 23:50 -0700
  Re: Java 8 Lambda with generic types Stone Zhong <stone.zhong@gmail.com> - 2016-08-28 00:02 -0700
    Re: Java 8 Lambda with generic types Arne Vajhøj <arne@vajhoej.dk> - 2016-08-28 07:46 -0400
      Re: Java 8 Lambda with generic types Steven Simpson <ss@my.domain.invalid> - 2016-08-28 15:00 +0100
        Re: Java 8 Lambda with generic types Lew <lewbloch@gmail.com> - 2016-08-30 22:25 -0700
          Re: Java 8 Lambda with generic types Steven Simpson <ss@my.domain.invalid> - 2016-08-31 17:19 +0100
  Re: Java 8 Lambda with generic types Steven Simpson <ss@my.domain.invalid> - 2016-08-28 08:19 +0100
  Re: Java 8 Lambda with generic types Stone Zhong <stone.zhong@gmail.com> - 2016-08-28 03:26 -0700
  Re: Java 8 Lambda with generic types Stone Zhong <stone.zhong@gmail.com> - 2016-08-28 07:45 -0700
    Re: Java 8 Lambda with generic types Arne Vajhøj <arne@vajhoej.dk> - 2016-08-28 13:22 -0400
  Re: Java 8 Lambda with generic types Stone Zhong <stone.zhong@gmail.com> - 2016-08-28 07:57 -0700
  Re: Java 8 Lambda with generic types Stone Zhong <stone.zhong@gmail.com> - 2016-08-28 10:43 -0700
    Re: Java 8 Lambda with generic types Arne Vajhøj <arne@vajhoej.dk> - 2016-08-30 20:35 -0400
  Re: Java 8 Lambda with generic types Stone Zhong <stone.zhong@gmail.com> - 2016-09-02 15:18 -0700

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