From jon.rafkind at hp.com  Tue Oct  7 01:19:42 2014
From: jon.rafkind at hp.com (Rafkind, Jon)
Date: Tue, 7 Oct 2014 01:19:42 +0000
Subject: generated lambda names - lambda$null$0
Message-ID: <C39D17F71FB39E488EA35B99FB02744751D0590C@G9W0766.americas.hpqcorp.net>

Tools that work with bytecode will inevitably come across the generated
lambda method names, and I noticed that lambdas nested inside other
lambdas have strange 'null' names in them.

public class x{
    interface T{
        int g();
    }

    public void test(){
        T t1 = () -> {
            T t2 = () -> 2;
            return 1;
        };
    }
}

The bytecode contains these two desugared lambda methods:

.method synthetic static private lambda$test$1 : ()I
.method synthetic static private lambda$null$0 : ()I

Where lambda$test$1 is the 't1' lambda, and lambda$null$0 is the 't2'
lambda. It's not the end of the world to have 'null' there, but since an
attempt at putting some useful info there is made maybe something better
than 'null' could be chosen.

Tested on jdk8u20.

BTW, javap cannot dissassemble/show any of the generated lambda code.
Perhaps hiding the generated lambda name from the user is ok, but there
is no way to see the method bodies. I was about to write my own
dissassembler based on the ASM library, but I found this nice github
project that works just fine: https://github.com/Storyyeller/Krakatau

From jonathan.gibbons at oracle.com  Tue Oct  7 01:30:44 2014
From: jonathan.gibbons at oracle.com (Jonathan Gibbons)
Date: Mon, 06 Oct 2014 18:30:44 -0700
Subject: generated lambda names - lambda$null$0
In-Reply-To: <C39D17F71FB39E488EA35B99FB02744751D0590C@G9W0766.americas.hpqcorp.net>
References: <C39D17F71FB39E488EA35B99FB02744751D0590C@G9W0766.americas.hpqcorp.net>
Message-ID: <54334244.2060901@oracle.com>


On 10/06/2014 06:19 PM, Rafkind, Jon wrote:
> BTW, javap cannot dissassemble/show any of the generated lambda code.

That sounds like a bug. Can you give a specific example?

-- Jon

From jonathan.gibbons at oracle.com  Tue Oct  7 01:51:40 2014
From: jonathan.gibbons at oracle.com (Jonathan Gibbons)
Date: Mon, 06 Oct 2014 18:51:40 -0700
Subject: generated lambda names - lambda$null$0
In-Reply-To: <54334244.2060901@oracle.com>
References: <C39D17F71FB39E488EA35B99FB02744751D0590C@G9W0766.americas.hpqcorp.net>
	<54334244.2060901@oracle.com>
Message-ID: <5433472C.6020305@oracle.com>


On 10/06/2014 06:30 PM, Jonathan Gibbons wrote:
>
> On 10/06/2014 06:19 PM, Rafkind, Jon wrote:
>> BTW, javap cannot dissassemble/show any of the generated lambda code.
>
> That sounds like a bug. Can you give a specific example?
>
> -- Jon
>

Partially answering my own question, for the example given in the 
original post, javap does show pretty much everything. The lambda method 
bodies are there: don't forget to use the -private option.

Source:
$ more play/x.java
public class x{
     interface T{
         int g();
     }

     public void test(){
         T t1 = () -> {
             T t2 = () -> 2;
             return 1;
         };
     }
}


javap:
$ javap -v -private play/x.class
Classfile /w/jjg/work/play/x.class
   Last modified Oct 6, 2014; size 886 bytes
   MD5 checksum 411cf2b7dea73faaee670b25e3739753
   Compiled from "x.java"
public class x
   minor version: 0
   major version: 52
   flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
    #1 = Methodref          #5.#19         // java/lang/Object."<init>":()V
    #2 = InvokeDynamic      #0:#24         // #0:g:()Lx$T;
    #3 = InvokeDynamic      #1:#24         // #1:g:()Lx$T;
    #4 = Class              #26            // x
    #5 = Class              #27            // java/lang/Object
    #6 = Class              #28            // x$T
    #7 = Utf8               T
    #8 = Utf8               InnerClasses
    #9 = Utf8               <init>
   #10 = Utf8               ()V
   #11 = Utf8               Code
   #12 = Utf8               LineNumberTable
   #13 = Utf8               test
   #14 = Utf8               lambda$test$1
   #15 = Utf8               ()I
   #16 = Utf8               lambda$null$0
   #17 = Utf8               SourceFile
   #18 = Utf8               x.java
   #19 = NameAndType        #9:#10         // "<init>":()V
   #20 = Utf8               BootstrapMethods
   #21 = MethodHandle       #6:#29         // invokestatic 
java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
   #22 = MethodType         #15            //  ()I
   #23 = MethodHandle       #6:#30         // invokestatic 
x.lambda$test$1:()I
   #24 = NameAndType        #31:#32        // g:()Lx$T;
   #25 = MethodHandle       #6:#33         // invokestatic 
x.lambda$null$0:()I
   #26 = Utf8               x
   #27 = Utf8               java/lang/Object
   #28 = Utf8               x$T
   #29 = Methodref          #34.#35        // 
java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
   #30 = Methodref          #4.#36         // x.lambda$test$1:()I
   #31 = Utf8               g
   #32 = Utf8               ()Lx$T;
   #33 = Methodref          #4.#37         // x.lambda$null$0:()I
   #34 = Class              #38            // 
java/lang/invoke/LambdaMetafactory
   #35 = NameAndType        #39:#42        // 
metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
   #36 = NameAndType        #14:#15        // lambda$test$1:()I
   #37 = NameAndType        #16:#15        // lambda$null$0:()I
   #38 = Utf8 java/lang/invoke/LambdaMetafactory
   #39 = Utf8               metafactory
   #40 = Class              #44            // 
java/lang/invoke/MethodHandles$Lookup
   #41 = Utf8               Lookup
   #42 = Utf8 
(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
   #43 = Class              #45            // java/lang/invoke/MethodHandles
   #44 = Utf8 java/lang/invoke/MethodHandles$Lookup
   #45 = Utf8               java/lang/invoke/MethodHandles
{
   public x();
     descriptor: ()V
     flags: ACC_PUBLIC
     Code:
       stack=1, locals=1, args_size=1
          0: aload_0
          1: invokespecial #1                  // Method 
java/lang/Object."<init>":()V
          4: return
       LineNumberTable:
         line 1: 0
         line 2: 4

   public void test();
     descriptor: ()V
     flags: ACC_PUBLIC
     Code:
       stack=1, locals=2, args_size=1
          0: invokedynamic #2,  0              // InvokeDynamic #0:g:()Lx$T;
          5: astore_1
          6: return
       LineNumberTable:
         line 7: 0
         line 11: 6

   private static int lambda$test$1();
     descriptor: ()I
     flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
     Code:
       stack=1, locals=1, args_size=0
          0: invokedynamic #3,  0              // InvokeDynamic #1:g:()Lx$T;
          5: astore_0
          6: iconst_1
          7: ireturn
       LineNumberTable:
         line 8: 0
         line 9: 6

   private static int lambda$null$0();
     descriptor: ()I
     flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
     Code:
       stack=1, locals=0, args_size=0
          0: iconst_2
          1: ireturn
       LineNumberTable:
         line 8: 0
}
SourceFile: "x.java"
InnerClasses:
   static #7= #6 of #4;                    // T=class x$T of class x
   public static final #41= #40 of #43;    // Lookup=class 
java/lang/invoke/MethodHandles$Lookup of class 
java/lang/invoke/MethodHandles
BootstrapMethods:
   0: #21 invokestatic 
java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
     Method arguments:
       #22 ()I
       #23 invokestatic x.lambda$test$1:()I
       #22 ()I
   1: #21 invokestatic 
java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
     Method arguments:
       #22 ()I
       #25 invokestatic x.lambda$null$0:()I
       #22 ()I


From robert.field at oracle.com  Tue Oct  7 02:16:51 2014
From: robert.field at oracle.com (Robert Field)
Date: Mon, 06 Oct 2014 19:16:51 -0700
Subject: generated lambda names - lambda$null$0
In-Reply-To: <C39D17F71FB39E488EA35B99FB02744751D0590C@G9W0766.americas.hpqcorp.net>
References: <C39D17F71FB39E488EA35B99FB02744751D0590C@G9W0766.americas.hpqcorp.net>
Message-ID: <54334D13.2040206@oracle.com>

No attempt was made to make the name user friendly or descriptive -- 
they were designed to be unique and for javac debugging purposes remain 
generally constant over small changes.

The "null" in the name is NOT a bug.

-Robert

On 10/06/14 18:19, Rafkind, Jon wrote:
> Tools that work with bytecode will inevitably come across the generated
> lambda method names, and I noticed that lambdas nested inside other
> lambdas have strange 'null' names in them.
>
> public class x{
>      interface T{
>          int g();
>      }
>
>      public void test(){
>          T t1 = () -> {
>              T t2 = () -> 2;
>              return 1;
>          };
>      }
> }
>
> The bytecode contains these two desugared lambda methods:
>
> .method synthetic static private lambda$test$1 : ()I
> .method synthetic static private lambda$null$0 : ()I
>
> Where lambda$test$1 is the 't1' lambda, and lambda$null$0 is the 't2'
> lambda. It's not the end of the world to have 'null' there, but since an
> attempt at putting some useful info there is made maybe something better
> than 'null' could be chosen.
>
> Tested on jdk8u20.
>
> BTW, javap cannot dissassemble/show any of the generated lambda code.
> Perhaps hiding the generated lambda name from the user is ok, but there
> is no way to see the method bodies. I was about to write my own
> dissassembler based on the ASM library, but I found this nice github
> project that works just fine: https://github.com/Storyyeller/Krakatau
>


From jon.rafkind at hp.com  Tue Oct  7 04:43:10 2014
From: jon.rafkind at hp.com (Rafkind, Jon)
Date: Tue, 7 Oct 2014 04:43:10 +0000
Subject: generated lambda names - lambda$null$0
References: <C39D17F71FB39E488EA35B99FB02744751D0590C@G9W0766.americas.hpqcorp.net>
	<54334244.2060901@oracle.com> <5433472C.6020305@oracle.com>
Message-ID: <C39D17F71FB39E488EA35B99FB02744751D06B10@G9W0766.americas.hpqcorp.net>

On 10/06/2014 06:52 PM, Jonathan Gibbons wrote:
> On 10/06/2014 06:30 PM, Jonathan Gibbons wrote:
>> On 10/06/2014 06:19 PM, Rafkind, Jon wrote:
>>> BTW, javap cannot dissassemble/show any of the generated lambda code.
>> That sounds like a bug. Can you give a specific example?
>>
>> -- Jon
>>
> Partially answering my own question, for the example given in the 
> original post, javap does show pretty much everything. The lambda method 
> bodies are there: don't forget to use the -private option.

Aha, I didn't know about -private. Thanks!

> Source:
> $ more play/x.java
> public class x{
>      interface T{
>          int g();
>      }
>
>      public void test(){
>          T t1 = () -> {
>              T t2 = () -> 2;
>              return 1;
>          };
>      }
> }
>
>
> javap:
> $ javap -v -private play/x.class
> Classfile /w/jjg/work/play/x.class
>    Last modified Oct 6, 2014; size 886 bytes
>    MD5 checksum 411cf2b7dea73faaee670b25e3739753
>    Compiled from "x.java"
> public class x
>    minor version: 0
>    major version: 52
>    flags: ACC_PUBLIC, ACC_SUPER
> Constant pool:
>     #1 = Methodref          #5.#19         // java/lang/Object."<init>":()V
>     #2 = InvokeDynamic      #0:#24         // #0:g:()Lx$T;
>     #3 = InvokeDynamic      #1:#24         // #1:g:()Lx$T;
>     #4 = Class              #26            // x
>     #5 = Class              #27            // java/lang/Object
>     #6 = Class              #28            // x$T
>     #7 = Utf8               T
>     #8 = Utf8               InnerClasses
>     #9 = Utf8               <init>
>    #10 = Utf8               ()V
>    #11 = Utf8               Code
>    #12 = Utf8               LineNumberTable
>    #13 = Utf8               test
>    #14 = Utf8               lambda$test$1
>    #15 = Utf8               ()I
>    #16 = Utf8               lambda$null$0
>    #17 = Utf8               SourceFile
>    #18 = Utf8               x.java
>    #19 = NameAndType        #9:#10         // "<init>":()V
>    #20 = Utf8               BootstrapMethods
>    #21 = MethodHandle       #6:#29         // invokestatic 
> java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
>    #22 = MethodType         #15            //  ()I
>    #23 = MethodHandle       #6:#30         // invokestatic 
> x.lambda$test$1:()I
>    #24 = NameAndType        #31:#32        // g:()Lx$T;
>    #25 = MethodHandle       #6:#33         // invokestatic 
> x.lambda$null$0:()I
>    #26 = Utf8               x
>    #27 = Utf8               java/lang/Object
>    #28 = Utf8               x$T
>    #29 = Methodref          #34.#35        // 
> java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
>    #30 = Methodref          #4.#36         // x.lambda$test$1:()I
>    #31 = Utf8               g
>    #32 = Utf8               ()Lx$T;
>    #33 = Methodref          #4.#37         // x.lambda$null$0:()I
>    #34 = Class              #38            // 
> java/lang/invoke/LambdaMetafactory
>    #35 = NameAndType        #39:#42        // 
> metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
>    #36 = NameAndType        #14:#15        // lambda$test$1:()I
>    #37 = NameAndType        #16:#15        // lambda$null$0:()I
>    #38 = Utf8 java/lang/invoke/LambdaMetafactory
>    #39 = Utf8               metafactory
>    #40 = Class              #44            // 
> java/lang/invoke/MethodHandles$Lookup
>    #41 = Utf8               Lookup
>    #42 = Utf8 
> (Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
>    #43 = Class              #45            // java/lang/invoke/MethodHandles
>    #44 = Utf8 java/lang/invoke/MethodHandles$Lookup
>    #45 = Utf8               java/lang/invoke/MethodHandles
> {
>    public x();
>      descriptor: ()V
>      flags: ACC_PUBLIC
>      Code:
>        stack=1, locals=1, args_size=1
>           0: aload_0
>           1: invokespecial #1                  // Method 
> java/lang/Object."<init>":()V
>           4: return
>        LineNumberTable:
>          line 1: 0
>          line 2: 4
>
>    public void test();
>      descriptor: ()V
>      flags: ACC_PUBLIC
>      Code:
>        stack=1, locals=2, args_size=1
>           0: invokedynamic #2,  0              // InvokeDynamic #0:g:()Lx$T;
>           5: astore_1
>           6: return
>        LineNumberTable:
>          line 7: 0
>          line 11: 6
>
>    private static int lambda$test$1();
>      descriptor: ()I
>      flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
>      Code:
>        stack=1, locals=1, args_size=0
>           0: invokedynamic #3,  0              // InvokeDynamic #1:g:()Lx$T;
>           5: astore_0
>           6: iconst_1
>           7: ireturn
>        LineNumberTable:
>          line 8: 0
>          line 9: 6
>
>    private static int lambda$null$0();
>      descriptor: ()I
>      flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
>      Code:
>        stack=1, locals=0, args_size=0
>           0: iconst_2
>           1: ireturn
>        LineNumberTable:
>          line 8: 0
> }
> SourceFile: "x.java"
> InnerClasses:
>    static #7= #6 of #4;                    // T=class x$T of class x
>    public static final #41= #40 of #43;    // Lookup=class 
> java/lang/invoke/MethodHandles$Lookup of class 
> java/lang/invoke/MethodHandles
> BootstrapMethods:
>    0: #21 invokestatic 
> java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
>      Method arguments:
>        #22 ()I
>        #23 invokestatic x.lambda$test$1:()I
>        #22 ()I
>    1: #21 invokestatic 
> java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
>      Method arguments:
>        #22 ()I
>        #25 invokestatic x.lambda$null$0:()I
>        #22 ()I
>
>
>


From neal at gafter.com  Mon Oct 13 18:12:13 2014
From: neal at gafter.com (Neal Gafter)
Date: Mon, 13 Oct 2014 11:12:13 -0700
Subject: Allocation of Lambdas that capture "this"
In-Reply-To: <CACuKZqHEvkrr6n__vVzyTvxvWzS0pNbd9e6YDxaiE7zLfo5Kow@mail.gmail.com>
References: <CAMaYbvLsWiYqXMWy0n37PC2y_Gsp9s6_merD2n81zgSf6Zu+dA@mail.gmail.com>
	<CACuKZqHEvkrr6n__vVzyTvxvWzS0pNbd9e6YDxaiE7zLfo5Kow@mail.gmail.com>
Message-ID: <CAD=nd8f2ac+B7MdEKubi_PZbWhzBDfyARv24Zvg4XeZ_ZGbi6g@mail.gmail.com>

On Wed, Aug 20, 2014 at 4:58 PM, Zhong Yu <zhong.j.yu at gmail.com> wrote:

> Is there any reason not to initialize the field directly? like
>
> final Consumer<Msg> readHandler = (Msg obj)-> {
>     this.doSomethingWith(obj);
>     ...
> };
>

You are not allowed to access "this" in a field initializer.

From zhong.j.yu at gmail.com  Tue Oct 14 18:36:05 2014
From: zhong.j.yu at gmail.com (Zhong Yu)
Date: Tue, 14 Oct 2014 13:36:05 -0500
Subject: Allocation of Lambdas that capture "this"
In-Reply-To: <CAD=nd8f2ac+B7MdEKubi_PZbWhzBDfyARv24Zvg4XeZ_ZGbi6g@mail.gmail.com>
References: <CAMaYbvLsWiYqXMWy0n37PC2y_Gsp9s6_merD2n81zgSf6Zu+dA@mail.gmail.com>
	<CACuKZqHEvkrr6n__vVzyTvxvWzS0pNbd9e6YDxaiE7zLfo5Kow@mail.gmail.com>
	<CAD=nd8f2ac+B7MdEKubi_PZbWhzBDfyARv24Zvg4XeZ_ZGbi6g@mail.gmail.com>
Message-ID: <CACuKZqGe5+=AbyDGUJC-Pwt5fdPyciFAYMOo+8SsFpVyS3+Ehw@mail.gmail.com>

On Mon, Oct 13, 2014 at 1:12 PM, Neal Gafter <neal at gafter.com> wrote:
> On Wed, Aug 20, 2014 at 4:58 PM, Zhong Yu <zhong.j.yu at gmail.com> wrote:
>>
>> Is there any reason not to initialize the field directly? like
>>
>> final Consumer<Msg> readHandler = (Msg obj)-> {
>>     this.doSomethingWith(obj);
>>     ...
>> };
>
>
> You are not allowed to access "this" in a field initializer.

Apparently it is allowed, according to javac.

What's not allowed is to reference a final field that "might not have
been initialized" when the lambda is constructed; which I think is
unnecessarily strict and inconvenient for many legitimate use cases.

    final Runnable r = ()->{ this.o.toString(); }; // javac error

    final Object o; // assigned in constructor

It can be worked around by obfuscating `this`

    final Runnable r = ()->{ (this).o.toString(); }; // ok

Zhong Yu
bayou.io

From sam at sampullara.com  Tue Oct 14 19:40:57 2014
From: sam at sampullara.com (Sam Pullara)
Date: Tue, 14 Oct 2014 12:40:57 -0700
Subject: Allocation of Lambdas that capture "this"
In-Reply-To: <CACuKZqGe5+=AbyDGUJC-Pwt5fdPyciFAYMOo+8SsFpVyS3+Ehw@mail.gmail.com>
References: <CAMaYbvLsWiYqXMWy0n37PC2y_Gsp9s6_merD2n81zgSf6Zu+dA@mail.gmail.com>
	<CACuKZqHEvkrr6n__vVzyTvxvWzS0pNbd9e6YDxaiE7zLfo5Kow@mail.gmail.com>
	<CAD=nd8f2ac+B7MdEKubi_PZbWhzBDfyARv24Zvg4XeZ_ZGbi6g@mail.gmail.com>
	<CACuKZqGe5+=AbyDGUJC-Pwt5fdPyciFAYMOo+8SsFpVyS3+Ehw@mail.gmail.com>
Message-ID: <CAMUF1SnxKczF+zPSk5q3m2zHy_-Lq_fFiLuppBkwPTYuZpav9Q@mail.gmail.com>

Since you can do this ? even if wrong ? with anonymous inner classes I
think it probably should be generally allowed.

Sam

final Runnable r = ()->{ (this).o.toString(); }; // javac error
final Object o; // assigned in constructor
{
  r.run();
}
public ZhongTest() {
  this.o = "";
}

java.lang.NullPointerException
	at spullara.ZhongTest.lambda$new$0(ZhongTest.java:10)
	at spullara.ZhongTest$$Lambda$1/693632176.run(Unknown Source)
	at spullara.ZhongTest.<init>(ZhongTest.java:13)


On Tue, Oct 14, 2014 at 11:36 AM, Zhong Yu <zhong.j.yu at gmail.com> wrote:

> On Mon, Oct 13, 2014 at 1:12 PM, Neal Gafter <neal at gafter.com> wrote:
> > On Wed, Aug 20, 2014 at 4:58 PM, Zhong Yu <zhong.j.yu at gmail.com> wrote:
> >>
> >> Is there any reason not to initialize the field directly? like
> >>
> >> final Consumer<Msg> readHandler = (Msg obj)-> {
> >>     this.doSomethingWith(obj);
> >>     ...
> >> };
> >
> >
> > You are not allowed to access "this" in a field initializer.
>
> Apparently it is allowed, according to javac.
>
> What's not allowed is to reference a final field that "might not have
> been initialized" when the lambda is constructed; which I think is
> unnecessarily strict and inconvenient for many legitimate use cases.
>
>     final Runnable r = ()->{ this.o.toString(); }; // javac error
>
>     final Object o; // assigned in constructor
>
> It can be worked around by obfuscating `this`
>
>     final Runnable r = ()->{ (this).o.toString(); }; // ok
>
> Zhong Yu
> bayou.io
>
>