ScalaMatsuri 2016 1/30(土) 14:30 - 14:45 「ScalaコードはJVMでどのように表現されているのか」で使用したスライドです。

1. Koichi
Sakata （阪田 浩一）
@jyukutyo
How
Scala
code
is
expressed
in
the
JVM
-­‐
ScalaMatsuri
2016
-­‐

2. 関ジャバです！
2
@jyukutyo
produced three Java framework books
one was translated into Korean
JUG Leader (KansaiJUG)
blog：Fight the Future
http://jyukutyo.hatenablog.com/
FURYU CORPORATION
age: 36
Koichi Sakata (阪田 浩一)
フリューの阪田です 関ジャバの会長です

3. I
♥
JVM

4. this
session
is
for
beginners
about
JVM
byte
codes
このセッションは
JVMのバイトコード初心者向けです

5. Do
you
know
what
happens
when
we
compile
Scala
code?
Scalaコードをコンパイルする時
何が起こるかご存じでしょうか？

6. Java
Scala
JRuby
Groovy
C
o
m
p
i
l
e
r
Class
file
cafe babe
0000 0032
0017 0100
JVM
Class
file
Class
file
Class
file
Class
file
Class
file § Runs
§ Interprets
§ Translates
bytecode
into
Native
Machine
Code

7. Have
you
ever
opened
a
class
file?
クラスファイルを開いたことはありますか

8. First,
let's
try
opening
a
class
file
from
a
simple
Java
code
Javaのクラスファイルを開いてみましょう

9. Hello
World
(Java)
public
class
HelloWorld
{
public
static
void
main(String[]
args)
{
System.out.println("Hello,
world!");
}
}
§ Compiled
into...
§ HelloWorld.class

10. open
HelloWorld.class
file
with
binary
editor
e.g.)
hexl-­‐find-­‐file
(Emacs)
クラスファイルをバイナリエディタで開く

11. cafe
babe
0000
0032
0017
0100
0a48
656c
6c6f
576f
726c
6407
0001
0100
106a
6176
612f
6c61
6e67
2f4f
626a
6563
7407
0003
0100
1048
656c
6c6f
576f
726c
642e
7363
616c
6101
001e
4c73
6361
6c61
2f72
6566
6c65
6374
2f53
6361
6c61
5369
676e
6174
7572
653b
0100
0562
7974
6573
0100
ef06
0115
3a51
2101
0209
0215
0921
0253
336d
593e
3c76
4e1d
3765
1505
1911
6102
1f66
5b42
2418
5050
0201
2109
3171
2144
0103
0d15
4121
0123
010a
0529
4155
0d1c
3770
2f3e
1448
0e5a
0a03
0f29
0122
6103
080e
0331
5111
2144
0106
670e
0c47
2e59
0503
1f31
1161
2111
387a
2516
3407
2242
0908

12. you
will
close
the
editor
right
away
すぐにエディタを閉じるでしょう

13. class
file
has
a
format
クラスファイルには
フォーマットがあります

14. ClassFile
{
u4
magic;
u2
minor_version;
u2
major_version;
u2
constant_pool_count;
cp_info
constant_pool[constant_pool_count-­‐1];
u2
access_flags;
u2
this_class;
u2
super_class;
u2
interfaces_count;
u2
interfaces[interfaces_count];
...
-­‐-­‐
u1
represents
one-­‐byte
quantity,
Hexadecimal
2
digit.

15. ...
u2
fields_count;
field_info
fields[fields_count];
u2
methods_count;
method_info
methods[methods_count];
u2
attributes_count;
attribute_info
attributes[attributes_count];
}
-­‐-­‐
u1
represents
one-­‐byte
quantity,
Hexadecimal
2
digit.
u1が1バイト
16進数では2桁になります

16. Let's
try
again

17. cafe
babe
0000
0032
0017
0100
0a48
656c
6c6f
576f
726c
6407
0001
0100
106a
6176
612f
6c61
6e67
2f4f
626a
6563
7407
0003
0100
1048
656c
6c6f
576f
726c
642e
7363
616c
6101
001e
4c73
6361
6c61
2f72
6566
6c65
6374
2f53
6361
6c61
5369
676e
6174
7572
653b
0100
0562
7974
6573
0100
ef06
0115
3a51
2101
0209
0215
0921
0253
336d
593e
3c76
4e1d
3765
1505
1911
6102
1f66
5b42
2418
5050
0201
2109
3171
2144
0103
0d15
4121
0123
010a
0529
4155
0d1c
3770
2f3e
1448
0e5a
0a03
0f29
0122
6103
080e
0331
5111
2144
0106
670e
0c47
2e59
0503
1f31
1161
2111
387a
2516
3407
2242
0908

18. cafe
babe
0000
0032
ClassFile
{
u4
magic;
u2
minor_version;
u2
major_version;

19. "magic"
is
always
"0xCAFEBABE"

20. major:
0x0032
=
50
minor:
0x0000
=
0
50.0
means
Java
SE
6
51.0
is
7,
52.0
is
8...

21. Yes!

22. but,
this
is
purgatory
でもこれは苦行です

23. Never
mind!
We
have
a
handy
tool!
便利なツールがあります！

24. javap
command
The
Java
Class
File
Disassembler
§ included
in
JDK
§ `javap
-­‐v
[FQCN]`
§ Scala
REPL
§ scala>
:javap
[FQCN]
§ equivalent
to
`javap
-­‐v`
http://docs.oracle.com/javase/7/docs/technotes/tools/windows/javap.html
javap - Java クラスファイル逆アセンブラ

25. so,
a
class
file
can
be
disassembled
to
Java
Classes
クラスファイルはJavaのクラスに
逆アセンブルできるのです

26. javap
-­‐v
HelloWorld

27. public
class
HelloWorld
minor
version:
0
major
version:
52
Constant
pool:
#1
=
Methodref
#6.#15
//
java/lang/Object."<init>":()V
#2
=
Fieldref
#16.#17
//
java/lang/System.out:Ljava/io/
PrintStream;
#3
=
String
#18
//
Hello,
world!
#4
=
Methodref
#19.#20
//
java/io/PrintStream.println:(Ljava/
lang/String;)V

28. Constant
pool
is
a
table
of
symbolic
information
コンスタントプールは
シンボル情報のテーブル

29. public
static
void
main(java.lang.String[]);
Code:
0:
getstatic
#2
3:
ldc
#3
5:
invokevirtual
#4
8:
return

30. JVM
instructions
aaload aastore aconst_null aload
anewarray areturn arraylength astore
athrow baload bastore bipush
caload castore checkcast d2f
d2i d2l dadd daload
dastore dcmp<op> dconst_<d> ddiv
dload dmul dneg ...

31. about
200
instructions

32. Since
first
release
of
Java,
added
instruction
is
...
Javaが最初にリリースされてから
追加されたJVM命令は...

33. only
ONE!

34. Initial
design
of
JVM
is
excellent!
JVMは初期設計から優秀だった！

35. instructions
of
method
call
invokevirtual
invoke
instance
method;
dispatched
based
on
class
invokeinterface invoke
interface
method
invokestatic invoke
static
method
invokespecial
invoke
method;
superclass,
private,
constructor...
invokedynamic invoke
dynamic
method

36. public
static
void
main(java.lang.String[]);
Code:
0:
getstatic
#2
3:
ldc
#3
5:
invokevirtual
#4
8:
return
-­‐-­‐
#0
=
index
of
Constant
pool

37. public
class
HelloWorld
Constant
pool:
#1
=
Methodref
#6.#15
//
java/lang/Object."<init>":()V
#2
=
Fieldref
#16.#17
//
java/lang/System.out:Ljava/io/
PrintStream;
#3
=
String
#18
//
Hello,
world!
#4
=
Methodref
#19.#20
//
java/io/PrintStream.println:(Ljava/
lang/String;)V
...

38. OK!
It's
Scala's
turn!

39. Hello
world

40. Hello
World
(Scala)
object
HelloWorld
{
def
main(args:
Array[String])
{
println("Hello,
world!")
}
}
§ Compiled
into...
§ HelloWorld.class
§ HelloWorld$.class

41. public
final
class
HelloWorld
Constant
pool:
#15
=
NameAndType
#13:#14
//
MODULE$:LHelloWorld$;
#16
=
Fieldref
#12.#15
//
HelloWorld$.MODULE$:LHelloWorld$;
#17
=
NameAndType
#9:#10
//
main:([Ljava/lang/String;)V
#18
=
Methodref
#12.#17
//
HelloWorld$.main:
([Ljava/lang/String;)V
...

42. public
static
void
main(java.lang.String[]);
0:
getstatic
#16
//
Field
HelloWorld$.
MODULE$:LHelloWorld$;
3:
aload_0
4:
invokevirtual
#18
//
Method
HelloWorld$.main:
([Ljava/lang/String;)V
7:
return
-­‐-­‐
4:
in
Java
HelloWorld$.MODULE$.main(arg);

43. public
final
class
HelloWorld$
-­‐-­‐
omit
Constant
pool
public
static
{};
0:
new
#2
//
class
HelloWorld$
3:
invokespecial
#12
//
Method
"<init>":()V
6:
return
-­‐-­‐
<init>
means
constructor

44.
public
void
main(java.lang.String[]);
0:
getstatic
#19
//
Field
scala/Predef$.MODULE$:
Lscala/Predef$;
3:
ldc
#21
//
String
Hello,
world!
5:
invokevirtual
#25
//
Method
scala/Predef$.println:
(Ljava/lang/Object;)V
8:
return

45. you
can
read
it!

46. The
following
samples
are
quoted
from
tutorials
in
Scala
official
site
http://docs.scala-­‐lang.org/tutorials/
これ以降で使用するサンプルは
Scalaの公式サイトのチュートリアルです

47. Traits

48. trait
Similarity
{
def
isSimilar(x:
Any):
Boolean
def
isNotSimilar(x:
Any):
Boolean
=
!isSimilar(x)
}
class
Point(xc:
Int,
yc:
Int)
extends
Similarity
{
var
x:
Int
=
xc
var
y:
Int
=
yc
def
isSimilar(obj:
Any)
=
obj.isInstanceOf[Point]
&&
obj.asInstanceOf[Point].x
==
x
}

49. § Compiled
into...
§ Similarity.class
§ Similarity$class.class
§ Point.class

50. javap
-­‐v

51. public
interface
Similarity
public
abstract
boolean
isSimilar(java.lang.Object);
public
abstract
boolean
isNotSimilar(java.lang.Object);

52. public
abstract
class
Similarity$class
public
static
boolean
isNotSimilar(Similarity,j.l.Object);
0:
aload_0
1:
aload_1
2:
invokeinterface
#13,
2
//
InterfaceMethod
Similarity.isSimilar:
(Ljava/lang/Object;)Z
7:
ifeq
14
10:
iconst_0
11:
goto
15
14:
iconst_1
15:
ireturn

53. a
trait
is
divided
into
an
interface
and
an
abstract
class
トレイトはインタフェースと
抽象クラスに分かれます

54. Case
Classes

55. abstract
class
Term
case
class
Var(name:
String)
extends
Term
case
class
Fun(arg:
String,
body:
Term)
extends
Term
case
class
App(f:
Term,
v:
Term)
extends
Term

56. § Compiled
into...
§ Term.class
§ App.class
§ App$.class
§ Fun.class
§ Fun$.class
§ Var.class
§ Var$.class

57. javap
-­‐v

58. public
class
App
extends
Term
implements
s.Product,s.Serializable
public
static
s.Option<scala.Tuple2<Term,
Term>>
unapply(App);
public
static
App
apply(Term,
Term);
public
...
tupled();
public
...
curried();
public
Term
f();
public
Term
v();
public
App
copy(Term,
Term);
public
j.l.String
productPrefix();
public
boolean
equals(j.l.Object);
...

59. public
final
class
App$
extends
s.r.AbstractFunction2<Term,
Term,
App>
implements
scala.Serializable
public
App
apply(Term,
Term);
0:
new
#23
//
class
App
3:
dup
4:
aload_1
5:
aload_2
6:
invokespecial
#26
//
Method
App."<init>":(LTerm;LTerm;)V
9:
areturn

60. Fun
and
Var
looks
the
same
as
App
FunとVarも同様の内容です

61. Scala
compiler
generates
many
functions
from
few
snippets
of
code
Scalaコンパイラは少ないコードから
多くの機能を生成しています

62. Pattern
Matching

63. object
MatchTest2
extends
App
{
def
matchTest(x:
Any):
Any
=
x
match
{
case
1
=>
"one"
case
"two"
=>
2
case
y:
Int
=>
"scala.Int"
}
println(matchTest("two"))
}

64. § Compiled
into...
§ MatchTest2.class
§ MatchTest2$.class
§ MatchTest2$delayedInit$body.class

65. javap
-­‐v

66. public
final
class
MatchTest2$
implements
scala.App
7:
invokestatic
#67
//
Method
BoxesRunTime.equals:..
10:
ifeq
19
13:
ldc
#69
//
String
one
15:
astore_3
16:
goto
46
19:
ldc
#71
//
String
two
21:
aload_2
22:
invokevirtual
#74
//
Method
java/lang/Object.equals:

67.
19:
ldc
#71
//
String
two
21:
aload_2
22:
invokevirtual
#74
//
Method
java/lang/Object.equals:
(Ljava/lang/Object;)Z
25:
ifeq
36
28:
iconst_2
32:
astore_3
33:
goto
46

68.
36:
aload_2
37:
instanceof
#76
//
class
java/lang/Integer
40:
ifeq
48
43:
ldc
#78
//
String
scala.Int
45:
astore_3
46:
aload_3
47:
areturn
...

69. Compiled
into
if
statements
if文へコンパイルしています

70. in
case
of
another
Pattern
Matching...
違うパターンマッチの場合

71. object
MatchTest1
{
def
matchTest(x:
Int):
String
=
x
match
{
case
1
=>
"one"
case
2
=>
"two"
case
_
=>
"many"
}
def
main(args:
Array[String])
{
println(matchTest(3))
}
}

72. javap
-­‐v

73.
3:
tableswitch
{
//
1
to
2
1:
34
2:
29
default:
24
}
24:
ldc
#16
//
String
many
26:
goto
36
29:
ldc
#18
//
String
two
31:
goto
36
34:
ldc
#20
//
String
one
36:
areturn

74. Compiled
into
a
switch
statement
switch文にコンパイルしています

75. Currying

76. object
CurryTest
{
def
filter(xs:
List[Int],
p:
Int
=>
Boolean):
List[Int]
=
if
(xs.isEmpty)
xs
else
if
(p(xs.head))
xs.head
::
filter(xs.tail,
p)
else
filter(xs.tail,
p)
def
modN(n:
Int)(x:
Int)
=
((x
%
n)
==
0)

77.
def
main(args:
Array[String])
{
val
nums
=
List(1,
2,
3,
4,
5,
6,
7,
8)
println(filter(nums,
modN(2)))
println(filter(nums,
modN(3)))
}
}

78. § Compiled
into...
§ CurryTest.class
§ CurryTest$.class
§ CurryTest$$anonfun$main$1.class
§ CurryTest$$anonfun$main$2.class

79. javap
-­‐v

80. public
final
class
CurryTest$$anonfun$main$1
extends
scala.runtime.AbstractFunction1$mcZI$sp
implements
scala.Serializable
public
boolean
apply$mcZI$sp(int);
3:
iconst_2
4:
iload_1
5:
invokevirtual
#33
//
Method
CurryTest$.modN:(II)Z
8:
ireturn

81. public
final
class
CurryTest$$anonfun$main$2
extends
scala.runtime.AbstractFunction1$mcZI$sp
implements
scala.Serializable
public
boolean
apply$mcZI$sp(int);
3:
iconst_3
4:
iload_1
5:
invokevirtual
#33
//
Method
CurryTest$.modN:(II)Z
8:
ireturn

82.
def
main(args:
Array[String])
{
val
nums
=
List(1,
2,
3,
4,
5,
6,
7,
8)
println(filter(nums,
modN(2)))
println(filter(nums,
modN(3)))
}
}

83. each
partial
application
creates
a
new
class
部分適用の箇所ごとに
クラスを生成しています

84. public
final
class
CurryTest$
...
public
void
main(java.lang.String[]);
63:
invokespecial
#82
//
Method
CurryTest$$anonfun$main$1.
"<init>":()V
66:
invokevirtual
#41
//
Method
filter:(Lscala/collection/
immutable/List;Lscala/Function1;)
Lscala/collection/immutable/List;
69:
invokevirtual
#86
//
Method
scala/Predef$.println:
(Ljava/lang/Object;)V

85. public
final
class
CurryTest$$anonfun$main$1
extends
scala.runtime.AbstractFunction1$mcZI$sp
implements
scala.Serializable

86. CurryTest$$anonfun
$main$2
is
same
$2も同様です

87.
81:
invokespecial
#89
//
Method
CurryTest$$anonfun$main$2.
"<init>":()V
84:
invokevirtual
#41
//
Method
filter:(Lscala/collection/
immutable/List;Lscala/Function1;)
Lscala/collection/immutable/List;
87:
invokevirtual
#86
//
Method
scala/Predef$.println:
(Ljava/lang/Object;)V

88. § Summary
§ JVM
is
excellent!
§ class
file
has
a
format
§ javap
is
useful
to
understand
Scala
at
the
bytecode
level
Try
typing
"javap"
after
you
compile
Scala
code

89. Thank
you!