Path: csiph.com!news.swapon.de!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
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
Organization: A noiseless patient Spider
Lines: 39
Message-ID: <usfa9d-k75.ln1@s.simpson148.btinternet.com>
References: <df44fc1a-9d48-4ba8-890e-a687d24062a9@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Info: mx02.eternal-september.org; posting-host="aeef5e178076fda4998e4379bb1adbab"; logging-data="23304"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX18n1cHEGaD447ysOBbvIhNt8SrqE/iYieg="
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0
In-Reply-To: <df44fc1a-9d48-4ba8-890e-a687d24062a9@googlegroups.com>
Cancel-Lock: sha1:m8upiglZolN33tUTsxZC9at8dD0=
Xref: csiph.com comp.lang.java.programmer:35484

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