1. Mastering Java Bytecode
Anton Arhipov | ZeroTurnaround

2. whoami
• Anton Arhipov
• Java Dev / Product Lead
• ZeroTurnaround, JRebel
• @antonarhipov @javarebel

3. Today – Java Core
• Mastering Java Bytecode
• The Future of Java on Multi-
Core, Lambdas, Spliterators and
Methods
• OpenJDK JVM Internals
• Invokedynamic Deep Dive

5. Why Bytecode?
• Know your platform!
• Create your own compiler?
• Programming model (AOP, ORM)
• Awesome tools (JRebel )
• … just bored?

6. THE INTRO

7. 1+2

8. 1+2
12+

9. 1+2
12+

10. 1+2
12+ PUSH 1
1

11. 1+2
12+ PUSH 1
PUSH 2
2
1

12. 1+2
12+ PUSH 1
PUSH 2
3
ADD

13. 1+2
12+ ICONST_1
ICONST_2
3
IADD

14. ?=1+2

15. TAXONOMY

16. Bytecode
• One-byte instructions
• 256 possible opcodes
• 200+ in use

17. TYPE OPERATION

18. TYPE OPERATION
• <TYPE> ::= b, s, c, i, l, f, d, a

19. TYPE OPERATION
• <TYPE> ::= b, s, c, i, l, f, d, a
• constant values (ldc, iconst_1)

20. TYPE OPERATION
• <TYPE> ::= b, s, c, i, l, f, d, a
• constant values (ldc, iconst_1)
• Local variables and stack interaction (load/store)
• Array operations (aload, astore)
• Math (add, sub, mul, div)
• Boolean/bitwise operations (iand, ixor)
• Comparisons (cmpg, cmpl, ifne, ifeq)
• Conversions (l2d, i2l)

21. Bytecode Taxonomy

22. Bytecode Taxonomy
Stack
Manipulation

23. Bytecode Taxonomy
Stack Flow
Manipulation Control

24. Bytecode Taxonomy
Stack Flow
Manipulation Control
Object
Model

25. Bytecode Taxonomy
Stack Flow
Manipulation Control
Object
Arithmetics
Model

26. Bytecode Taxonomy
Stack Flow
Manipulation Control
monitorenter
monitorexit
Object
Arithmetics
Model

27. TOOLING

28. javap
• Java class file disassembler
• Used with no options shows class structure
only
– Methods, superclass, interfaces, etc
• -c shows the bytecode
• -private shows all methods and members
• -s prints internal signatures
• -l prints line numbers and local variable
tables

29. HELLO WORLD!

31. C:workgeeconclasses>javap Hello -c

32. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return

33. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code: the default constructor
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return

34. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code: push this to stack
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return

35. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
invoke <init> on this

36. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return

37. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String Hello, World!
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

38. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
get static field
public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String Hello, World!
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

39. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String Hello, World!
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
load string to the stack

40. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String Hello, World!
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
invoke method with parameter

41. C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String Hello, World!
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

42. What’s #1,#2, etc ?
C:workgeeconclasses>javap Hello -c
Compiled from "Hello.java"
public class Hello extends java.lang.Object{
public Hello();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String Hello, World!
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V

43. C:workgeeconclasses>javap Hello -c -verbose

44. C:workgeeconclasses>javap Hello -c -verbose

45. C:workgeeconclasses>javap Hello -c -verbose
Compiled from "Hello.java“
public class Hello extends java.lang.Object
SourceFile: "Hello.java"
minor version: 0
major version: 50
Constant pool:
const #1 = Method #6.#20; // java/lang/Object."<init>":()V
const #2 = Field #21.#22; // java/lang/System.out:Ljava/io/PrintStream;
const #3 = String #23; // Hello, World!
const #4 = Method #24.#25; // java/io/PrintStream.println:(Ljava/lang/String;)V
const #5 = class #26; // Hello
const #6 = class #27; // java/lang/Object
const #7 = Asciz <init>;
const #8 = Asciz ()V;

46. C:workgeeconclasses>javap Hello -c -verbose
Compiled from "Hello.java“
public class Hello extends java.lang.Object
SourceFile: "Hello.java"
minor version: 0
major version: 50
Constant pool:
const #1 = Method #6.#20; // java/lang/Object."<init>":()V
const #2 = Field #21.#22; // java/lang/System.out:Ljava/io/PrintStream;
const #3 = String #23; // Hello, World!
const #4 = Method #24.#25; // java/io/PrintStream.println:(Ljava/lang/String;)V
const #5 = class #26; // Hello
const #6 = class #27; // java/lang/Object
const #7 = Asciz <init>;
const #8 = Asciz ()V;

47. C:workgeeconclasses>javap Hello -c -verbose
…
public Hello();
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
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LHello;

48. C:workgeeconclasses>javap Hello -c -verbose
…
public Hello();
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
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LHello;

49. C:workgeeconclasses>javap Hello -c -verbose
…
public Hello();
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
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LHello;

50. C:workgeeconclasses>javap Hello -c -verbose
…
public static void main(java.lang.String[]);
Code:
Stack=2, Locals=1, Args_size=1
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String Hello, World!
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
8: return
LineNumberTable:
line 4: 0
line 5: 8
LocalVariableTable:
Start Length Slot Name Signature
0 9 0 args [Ljava/lang/String;

51. MODEL OF
COMPUTATION

52. Stack Machine

53. Stack Machine
• JVM is a stack-based machine

54. Stack Machine
• JVM is a stack-based machine
• Each thread has a stack

55. Stack Machine
• JVM is a stack-based machine
• Each thread has a stack
• Stack stores frames

56. Stack Machine
• JVM is a stack-based machine
• Each thread has a stack
• Stack stores frames
• Frame is created on method invocation

57. Stack Machine
• JVM is a stack-based machine
• Each thread has a stack
• Stack stores frames
• Frame is created on method invocation
• Frame consists of:
– Operand stack
– Array of local variables

58. The Frame
Local variables
0 1 2 … N
Operand stack
#1
Constant
Pool

59. public java.lang.String getName();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: getfield #2; //Field name:Ljava/lang/String;
4: areturn
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LGet;

60. 0 1 2 3 4
aload_0 getfield 00 02 areturn
public java.lang.String getName();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: getfield #2; //Field name:Ljava/lang/String;
4: areturn
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LGet;

61. 0 1 2 3 4
2A B4 00 02 B0
public java.lang.String getName();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: getfield #2; //Field name:Ljava/lang/String;
4: areturn
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LGet;

62. public java.lang.String getName();
Code:
Stack=1, Locals=1, Args_size=1
0: aload_0
1: getfield #2; //Field name:Ljava/lang/String;
4: areturn
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LGet;

63. STACK CRUNCHING

64. dup A
pop B
swap
dup_x1
dup2_x1

65. dup A
pop A
swap B
dup_x1
dup2_x1

66. dup A
pop B
swap
dup_x1
dup2_x1

67. dup B
pop A
swap
dup_x1
dup2_x1

68. dup B
pop A
swap B
dup_x1
dup2_x1

69. dup B
pop A
swap B
dup_x1 B
dup2_x1 A

70. dup2_x2
How do you
swap doubles?

71. dup2_x2

72. dup2_x2
dconst_0
0.0

73. dup2_x2
dconst_0
dconst_1 1.0
0.0

74. dup2_x2
dconst_0
dconst_1 1.0
swap
0.0

75. dup2_x2
dconst_0
dconst_1 1.0
swap not allowed!
0.0

76. dup2_x2
dconst_0
dconst_1 1.0
swap2
0.0

77. dup2_x2
dconst_0
dconst_1 1.0
doesn’t
swap2 exist
0.0

78. dup2_x2
dconst_0
dconst_1 1.0
dup2_x2
0.0
1.0

79. dup2_x2
dconst_0
dconst_1 0.0
dup2_x2
pop2 1.0

80. dup2_x2
dconst_0
dconst_1 0.0
dup2_x2
pop2 1.0
profit! 

81. LOCAL VARIABLES

82. Local Variables

83. Local Variables
public int calculate(int);
Code:
Stack=2, Locals=2, Args_size=2
…
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LLocalVariables;
0 5 1 value I

84. Local Variables
public int calculate(int);
Code:
Stack=2, Locals=2, Args_size=2
…
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LLocalVariables;
0 5 1 value I

85. Local Variables
public int calculate(int);
Code:
Stack=2, Locals=2, Args_size=2
…
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LLocalVariables;
0 5 1 value I

86. Local Variables
The table
public int calculate(int);
Code: maps
Stack=2, Locals=2, Args_size=2 numbers to
…
names
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LLocalVariables;
0 5 1 value I

87. Local Variables
public int calculate(int);
Code:
Stack=2, Locals=2, Args_size=2 Sized explicitly
…
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this LLocalVariables;
0 5 1 value I

88. Local Variables Stack
var value depth value
ldc "Hello"
0 0
astore_0
1 iconst_1 1
astore_1
2 aload_0 2
3 3
4 4

89. Local Variables Stack
var value depth value
ldc "Hello"
0 0 "Hello"
astore_0
1 iconst_1 1
astore_1
2 aload_0 2
3 3
4 4

90. Local Variables Stack
var value depth value
ldc "Hello"
0 "Hello" 0
astore_0
1 iconst_1 1
astore_1
2 aload_0 2
3 3
4 4

91. Local Variables Stack
var value depth value
ldc "Hello"
0 "Hello" 0 1
astore_0
1 iconst_1 1
astore_1
2 aload_0 2
3 3
4 4

92. Local Variables Stack
var value depth value
ldc "Hello"
0 "Hello" 0
astore_0
1 1 iconst_1 1
astore_1
2 aload_0 2
3 3
4 4

93. Local Variables Stack
var value depth value
ldc "Hello"
0 "Hello" 0 "Hello"
astore_0
1 1 iconst_1 1
astore_1
2 aload_0 2
3 3
4 4

94. load
Local
Variables Stack
Table
store

95. OBJECTS

96. Object Initialization
new
0xBB
<init>
Instance initialization method
<clinit>
Class and interface
initialization method

97. Object Initialization: static {}
static {};
Code:
0: iconst_1
1: putstatic #2; //Field a:I
4: iconst_2
5: putstatic #3; //Field b:I
8: return

98. Object Initialization: static {}
<clinit>
static {};
Code:
0: iconst_1
1: putstatic #2; //Field a:I
4: iconst_2
5: putstatic #3; //Field b:I
8: return

99. Object Initialization: new

100. Object Initialization: new

101. Object Initialization: new
public Initializer();
Code:

102. Object Initialization: new
public Initializer();
Code:
0: aload_0

103. Object Initialization: new
public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V

104. Object Initialization: new
public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: aload_0

105. Object Initialization: new
public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: aload_0
5: new #2; //class java/lang/Object
8: dup

106. Object Initialization: new
public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: aload_0
5: new #2; //class java/lang/Object
8: dup
9: invokespecial #1; //Method java/lang/Object."<init>":()V
12: putfield #3; //Field o:Ljava/lang/Object;

107. Object Initialization: new
public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: aload_0
5: new #2; //class java/lang/Object
8: dup
9: invokespecial #1; //Method java/lang/Object."<init>":()V
12: putfield #3; //Field o:Ljava/lang/Object;
15: return

108. Object Initialization: new
public Initializer();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: aload_0
5: new #2; //class java/lang/Object
8: dup
9: invokespecial #1; //Method java/lang/Object."<init>":()V
12: putfield #3; //Field o:Ljava/lang/Object;
15: return

109. Object Initialization: {}

110. Object Initialization: {}

111. Object Initialization: {}
public Initializer(int);
Code:
0:aload_0
1:invokespecial #1; // ..<init>
4:aload_0
5:iconst_1
6:putfield #2; //Field a:I
9:aload_0
10:iconst_2
11: putfield #3; //Field c:I
14:aload_0
15:iload_1
16:putfield #4; //Field b:I
19:return

113. There’s no initializer

114. METHOD
INVOCATION

115. invokeXXX
• invokestatic
• invokespecial
• invokevirtual
• invokeinterface
• invokedynamic

116. invokestatic
• invokestatic
• invokespecial
• invokevirtual Integer.valueOf(“42”)
• invokeinterface
• invokedynamic

117. invokespecial
• invokestatic <init>
• invokespecial
• invokevirtual private void foo();
• invokeinterface
• invokedynamic super.method();

118. invokevirtual
class A
• invokestatic A/method1
A/method2
• invokespecial
• invokevirtual
• invokeinterface
• invokedynamic

119. invokevirtual
class A
• invokestatic A/method1
A/method2
• invokespecial
class B
• invokevirtual
• invokeinterface
• invokedynamic

120. invokevirtual
class A
• invokestatic A/method1
A/method2
• invokespecial
class B
• invokevirtual A/method1
B/method2
• invokeinterface B/method3
• invokedynamic

121. invokeinterface
class A
• invokestatic A/method1
A/method2
• invokespecial
class B impl X
• invokevirtual A/method1
B/method2
• invokeinterface B/method3
X/methodX
• invokedynamic

122. invokeinterface
class A
• invokestatic A/method1
A/method2
• invokespecial
class B impl X
• invokevirtual A/method1
• invokeinterface
B/method2
B/method3
D impl X
X/methodX D/method1
• invokedynamic X/methodX

123. invokeinterface
class A
• invokestatic A/method1
A/method2
• invokespecial
class B impl X
• invokevirtual A/method1
• invokeinterface
B/method2
B/method3
D impl X
X/methodX D/method1
• invokedynamic X/methodX

124. invokeinterface
class A
• invokestatic A/method1
A/method2
• invokespecial
class B impl X
• invokevirtual A/method1
• invokeinterface
B/method2
B/method3
D impl X
X/methodX D/method1
• invokedynamic X/methodX
Efficient Implementation of Java Interfaces: Invokeinterface Considered
Harmless, Bowen Alpern, Anthony Cocchi, Stephen Fink, David Grove, and
Derek Lieber, OOPSLA’01

125. Method Invocation

126. Method Invocation
obj.method(param1, param2);

127. Method Invocation
obj.method(param1, param2);

128. Method Invocation
obj.method(param1, param2);
push obj
push param1
push param2
call method

129. Method Invocation
obj.method(param1, param2);
obj
push obj
push param1
push param2
call method

130. Method Invocation
obj.method(param1, param2);
param1
push obj
obj
push param1
push param2
call method

131. Method Invocation
obj.method(param1, param2);
param2
push obj param1
push param1
push param2 obj
call method

132. Method Invocation
obj.method(param1, param2);
obj?
push obj
push param1
push param2
call method

133. Method Invocation
this.add(1, 2);
0: aload_0
1: iconst_1
2: iconst_2
3: invokevirtual #2; //Method add:(II)I

134. INNER CLASSES

135. Inner Classes

136. Inner Classes

137. Inner Classes
class Car$Engine extends j.l.Object{
final Car this$0;
Car$Engine(Car);
public void start();
Code:
0: aload_0
1: getfield #1; //Field this$0:LCar;
4: invokestatic #3; // Car.access$000:(LCar;)V
7: return
}

138. Inner Classes
public class Car extends j.l.Object{
public Car();
private void move();
class Car$Engine extends j.l.Object{
final Car this$0; static void access$000(Car);
Code:
Car$Engine(Car); 0: aload_0
1: invokespecial #1; // move: ()V;
public void start(); 4: return
Code: }
0: aload_0
1: getfield #1; //Field this$0:LCar;
4: invokestatic #3; // Car.access$000:(LCar;)V
7: return
}

139. Inner Classes
public class Car extends j.l.Object{
public Car();
private void move();
class Car$Engine extends j.l.Object{
final Car this$0; static void access$000(Car);
Code:
Car$Engine(Car); 0: aload_0
1: invokespecial #1; // move: ()V;
public void start(); 4: return
Code: }
0: aload_0
1: getfield #1; //Field this$0:LCar;
4: invokestatic #3; // Car.access$000:(LCar;)V
7: return
}

140. “HOW DO THEY DO THAT?”

141. object Singleton {
def test={}
}

142. object Singleton {
def test={}
}
$> scalac Singleton.scala
Singleton.class Singleton$.class

143. public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$;
3: invokevirtual #13; //Method Singleton$.test:()V
6: return
}

144. public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$;
3: invokevirtual #13; //Method Singleton$.test:()V
6: return
}

145. public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$;
3: invokevirtual #13; //Method Singleton$.test:()V
6: return
}

146. public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$;
3: invokevirtual #13; //Method Singleton$.test:()V
6: return
}
public final class Singleton$ extends java.lang.Object implements
scala.ScalaObject {
public static final Singleton$ MODULE$;
public static {};
Code:
0: new #9; //class Singleton$
3: invokespecial #12; //Method "<init>":()V
6: return
public void test();
private Singleton$();
}

147. public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$;
3: invokevirtual #13; //Method Singleton$.test:()V
6: return
}
public final class Singleton$ extends java.lang.Object implements
scala.ScalaObject {
public static final Singleton$ MODULE$;
public static {};
Code:
0: new #9; //class Singleton$
3: invokespecial #12; //Method "<init>":()V
6: return
public void test();
private Singleton$();
}

148. public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$;
3: invokevirtual #13; //Method Singleton$.test:()V
6: return
}
public final class Singleton$ extends java.lang.Object implements
scala.ScalaObject {
public static final Singleton$ MODULE$;
public static {};
Code:
0: new #9; //class Singleton$
3: invokespecial #12; //Method "<init>":()V
6: return
public void test();
private Singleton$();
}

149. public final class Singleton extends java.lang.Object {
public static final void test();
Code:
0: getstatic #11; //Field Singleton$.MODULE$:LSingleton$;
3: invokevirtual #13; //Method Singleton$.test:()V
6: return
}
public final class Singleton$ extends java.lang.Object implements
scala.ScalaObject {
public static final Singleton$ MODULE$;
public static {};
public void test();
private Singleton$();
Code:
0: aload_0
1: invokespecial #17; //Method java/lang/Object."<init>":()V
4: aload_0
5: putstatic #19; //Field MODULE$:LSingleton$;
8: return

150. object Singleton {
def test={}
}

151. public class Singleton {
public void test(){
Singleton$.MODULE$.test();
}
}
object Singleton {
def test={}
}

152. public class Singleton {
public void test(){
Singleton$.MODULE$.test();
}
}
public final class Singleton$
object Singleton { implements scala.ScalaObject {
def test={} public static final Singleton$ MODULE$;
} static { new Singleton$(); }
private Singleton$(){
MODULE$ = this;
}
public void test() {
}
}

153. class Groovy { }

154. class Groovy { }
$> groovyc Groovy.groovy
$> javap –c –p Groovy

155. class Groovy { }
$> groovyc Groovy.groovy
$> javap –c –p Groovy
public class Test extends java.lang.Object implements groovy.lang.GroovyObject{
private static org.codehaus.groovy.reflection.ClassInfo $staticClassInfo;
private transient groovy.lang.MetaClass metaClass;
public static java.lang.Long __timeStamp;
public static java.lang.Long __timeStamp__239_neverHappen1304807931117;
private static java.lang.ref.SoftReference $callSiteArray;
private static java.lang.Class $class$groovy$lang$MetaClass;
private static java.lang.Class $class$Test;
private static java.lang.Class $class$java$lang$String;
public java.lang.Object this$dist$invoke$2(java.lang.String, java.lang.Object);
public void this$dist$set$2(java.lang.String, java.lang.Object);
public java.lang.Object this$dist$get$2(java.lang.String);
protected groovy.lang.MetaClass $getStaticMetaClass();
public groovy.lang.MetaClass getMetaClass();
public void setMetaClass(groovy.lang.MetaClass);
public java.lang.Object invokeMethod(java.lang.String, java.lang.Object);
public java.lang.Object getProperty(java.lang.String);
public void setProperty(java.lang.String, java.lang.Object);

156. OBJECTWEB ASM

157. SLIDES
GOTO IDE
SLIDES
IDE: DEMO

158. https://github.com/antonarhipov

159. @antonarhipov
anton@zeroturnaround.com