Java bytecode lies at the foundation of the the entire Java ecosystem. Regardless of what language and tools you use, if you run on the JVM, you’re using Java bytecode. Although understanding bytecode is not a requirement for all developers, a deeper understanding of how your code runs on the JVM can make understanding and resolving certain types of issues much easier. Understanding bytecode also opens the door to more-advanced techniques such as bytecode instrumentation via JVMTI and writing your own Java agent. This session starts at the very beginning and covers all the basics, with a heavy emphasis on examples.

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and Oracle undertakes no duty to update any statement in light of new information or future events.
Safe Harbor
Copyright © 2019 Oracle and/or its affiliates.

2. Java Bytecode Crash Course [DEV4312]
Principal Member of Technical Staff
Java Platform Group
September 16, 2019
David Buck
Copyright © 2019 Oracle and/or its affiliates.

3. JVM Sustaining Engineer
OpenJDK 8 Update Project
Maintainer
JavaOne Rock Star
Co-author of Oracle WebLogic
Server 11g 構築・運用ガイド
@DavidBuckJP
https://blogs.oracle.com/buck/
Who am I? David Buck (left)

4. Agenda
Introduction
Foundational Concepts
Examples

5. Introduction

6. Why?

7. Why?
lingua franca of Java platform

8. Why?
lingua franca of Java platform
javap output

9. Why?
lingua franca of Java platform
javap output
foundation for future study
bridge methods
type eraser
debugging

10. javap
-v option to “disassemble” bytecode
-p option to see private methods
use latest version

11. Disclaimer

12. Foundational Concepts

13. What is bytecode?
byte-sized opcodes
Only 256 possible opcodes
operands can be 8 or 16 bit

14. stack machine

15. stack machine
push 1
1

16. stack machine
push 2
1
2

17. stack machine
add
3

18. stack machine
Convenient
abstract away CPU register details
free liveness analysis

19. stack machine
Not that rare
RPN notation

20. stack machine
Not that rare
RPN notation
PostScript

21. stack machine
Not that rare
RPN notation
PostScript
Forth

22. local variables
store / load commands
used to access method arguments

23. Examples

24. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}

25. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return

26. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return

27. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return

28. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
?

29. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
?
0

30. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
0

31. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
0
0

32. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
0
0
100

33. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
0

34. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
1

35. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
1

36. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
2

37. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
3

38. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
100

39. Let’s go for a spin!
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
100

40. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}

41. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}

42. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}
void dspin();
stack=4, locals=3,
args_size=1
0: dconst_0
1: dstore_1
2: dload_1
3: ldc2_w #2
// double 100.0d
6: dcmpg
7: ifge 17
10: dload_1
11: dconst_1
12: dadd
13: dstore_1
14: goto 2
17: return

43. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}
void dspin();
stack=4, locals=3,
args_size=1
0: dconst_0
1: dstore_1
2: dload_1
3: ldc2_w #2
// double 100.0d
6: dcmpg
7: ifge 17
10: dload_1
11: dconst_1
12: dadd
13: dstore_1
14: goto 2
17: return

44. data “categories”
Size 1
boolean
byte
char
short
int
float
reference
returnAddress
Size 2
long
double

45. int spin
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
i
int 1
int 0

46. Double Spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}
void dspin();
stack=4, locals=3,
args_size=1
0: dconst_0
1: dstore_1
2: dload_1
3: ldc2_w #2
// double 100.0d
6: dcmpg
7: ifge 17
10: dload_1
11: dconst_1
12: dadd
13: dstore_1
14: goto 2
17: returnStackLocals
this
i (1 of 2)
d1 (2 of 2)
d1 (1 of 2)
i (2 of 2)
d0 (2 of 2)
d0 (1 of 2)

47. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}
void dspin();
stack=4, locals=3,
args_size=1
0: dconst_0
1: dstore_1
2: dload_1
3: ldc2_w #2
// double 100.0d
6: dcmpg
7: ifge 17
10: dload_1
11: dconst_1
12: dadd
13: dstore_1
14: goto 2
17: returnStackLocals
this
i (1 of 2)
d1 (2 of 2)
d1 (1 of 2)
i (2 of 2)
d0 (2 of 2)
d0 (1 of 2)

48. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}
void dspin();
stack=4, locals=3,
args_size=1
0: dconst_0
1: dstore_1
2: dload_1
3: ldc2_w #2
// double 100.0d
6: dcmpg
7: ifge 17
10: dload_1
11: dconst_1
12: dadd
13: dstore_1
14: goto 2
17: returnStackLocals
this
i (1 of 2)
d1 (2 of 2)
d1 (1 of 2)
i (2 of 2)
d0 (2 of 2)
d0 (1 of 2)

49. constant pool loads

50. constant pool loads
Category 1
ldc
ldc_w
Category 2
ldc2_w

51. constant pool loads
Category 1
ldc
ldc_w
Category 2
ldc2_w

52. constant pool loads
Category 1
ldc
ldc_w
Category 2
ldc2_w

53. constant pool loads
Category 1
ldc
ldc_w
Category 2
ldc2_w

54. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}
void dspin();
stack=4, locals=3,
args_size=1
0: dconst_0
1: dstore_1
2: dload_1
3: ldc2_w #2
// double 100.0d
6: dcmpg
7: ifge 17
10: dload_1
11: dconst_1
12: dadd
13: dstore_1
14: goto 2
17: returnStackLocals
this
i (1 of 2)
d1 (2 of 2)
d1 (1 of 2)
i (2 of 2)
d0 (2 of 2)
d0 (1 of 2)

55. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}
void dspin();
stack=4, locals=3,
args_size=1
0: dconst_0
1: dstore_1
2: dload_1
3: ldc2_w #2
// double 100.0d
6: dcmpg
7: ifge 17
10: dload_1
11: dconst_1
12: dadd
13: dstore_1
14: goto 2
17: returnStackLocals
this
i (1 of 2)
d1 (2 of 2)
d1 (1 of 2)
i (2 of 2)
d0 (2 of 2)
d0 (1 of 2)

56. but some types are more equal than
others…opcode byte short int long float double char reference
Tipush bipush sipush
Tconst iconst lconst fconst dconst aconst
Tload iload lload fload dload aload
Tstore istore lstore fstore dstore astore
Tinc iinc
Taload baload saload iaload laload faload daload caload aaload
Tastore bastore sastore iastore lastore fastore dastore castore aastore
Tadd iadd ladd fadd dadd
Tsub isub lsub fsub dsub
Tmul imul lmul fmul dmul
Tdiv idiv ldiv fdiv ddiv
Trem irem lrem frem drem
Tneg ineg lneg fneg dneg
Tshl ishl lshl
Tshr ishr lshr
Tushr iushr lushr
Tand iand land
Tor ior lor
Txor ixor lxor
i2T i2b i2s i2l i2f i2d
l2T l2i l2f l2d
f2T f2i f2l f2d
d2T d2i d2l d2f
Tcmp lcmp
Tcmpl fcmpl dcmpl
Tcmpg fcmpg dcmpg
if_TcmpOP if_icmpOP if_acmpOP
Treturn ireturn lreturn freturn dreturn areturn

57. but some types are more equal than
others…
opcode byte short int long float double char reference
Tipush bipush sipush
Tconst iconst lconst fconst dconst aconst
Tload iload lload fload dload aload
Tstore istore lstore fstore dstore astore
Tinc iinc
Taload baload saload iaload laload faload daload caload aaload
Tastore bastore sastore iastore lastore fastore dastore castore aastore
Tadd iadd ladd fadd dadd
Tsub isub lsub fsub dsub
Tmul imul lmul fmul dmul
Tdiv idiv ldiv fdiv ddiv
Trem irem lrem frem drem
Tneg ineg lneg fneg dneg
Tshl ishl lshl
Tshr ishr lshr
Tushr iushr lushr
Tand iand land
Tor ior lor
Txor ixor lxor
i2T i2b i2s i2l i2f i2d
l2T l2i l2f l2d
f2T f2i f2l f2d
d2T d2i d2l d2f
Tcmp lcmp
Tcmpl fcmpl dcmpl
Tcmpg fcmpg dcmpg
if_TcmpOP if_icmpOP if_acmpOP
Treturn ireturn lreturn freturn dreturn areturn

58. but some types are more equal than
others…
Actual type
Computational
type
Category
Boolean int 1
byte int 1
char int 1
short int 1
int int 1
float float 1
reference reference 1
returnAddress returnAddress 1
long long 2
double double 2

59. int spin
void spin() {
int i;
for (i = 0; i < 100; i++) {
;// empty
}
}
void spin();
Code:
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 14
8: iinc 1, 1
11: goto 2
14: return
StackLocals
this
i
int 1
int 0

60. double spin
void dspin() {
double i;
for (i = 0.0; i < 100.0; i++) {
; //empty
}
}
void dspin();
stack=4, locals=3,
args_size=1
0: dconst_0
1: dstore_1
2: dload_1
3: ldc2_w #2
// double 100.0d
6: dcmpg
7: ifge 17
10: dload_1
11: dconst_1
12: dadd
13: dstore_1
14: goto 2
17: returnStackLocals
this
i (1 of 2)
d1 (2 of 2)
d1 (1 of 2)
i (2 of 2)
d0 (2 of 2)
d0 (1 of 2)

61. short spin
void sspin() {
short i;
for (i = 0; i < 100; i++) {
; //empty
}
}

62. short spin
void sspin() {
short i;
for (i = 0; i < 100; i++) {
; //empty
}
}

63. short spin
void sspin() {
short i;
for (i = 0; i < 100; i++) {
; //empty
}
}
void sspin();
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 16
8: iload_1
9: iconst_1
10: iadd
11: i2s
12: istore_1
13: goto 2
16: returnStackLocals
this
i
int 1
int 0

64. short spin
void sspin() {
short i;
for (i = 0; i < 100; i++) {
; //empty
}
}
void sspin();
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 16
8: iload_1
9: iconst_1
10: iadd
11: i2s
12: istore_1
13: goto 2
16: returnStackLocals
this
i
int 1
int 0

65. short spin
void sspin() {
short i;
for (i = 0; i < 100; i++) {
; //empty
}
}
void sspin();
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 16
8: iload_1
9: iconst_1
10: iadd
11: i2s
12: istore_1
13: goto 2
16: returnStackLocals
this
i
int 1
int 0

66. short spin
void sspin() {
short i;
for (i = 0; i < 100; i++) {
; //empty
}
}
void sspin();
stack=2, locals=2,
args_size=1
0: iconst_0
1: istore_1
2: iload_1
3: bipush 100
5: if_icmpge 16
8: iload_1
9: iconst_1
10: iadd
11: i2s
12: istore_1
13: goto 2
16: returnStackLocals
this
i
int 1
int 0

67. constant pool fun
void useManyNumeric() {
int i = 100;
int j = 1000000;
long l1 = 1;
long l2 = 0xffffffff;
double d = 2.2;
// ...do some calculations...
}
void useManyNumeric();
0: bipush 100
2: istore_1
3: ldc #2
// int 1000000
5: istore_2
6: lconst_1
7: lstore_3
8: ldc2_w #3
// long -1l
11: lstore 5
13: ldc2_w #5
// double 2.2d
16: dstore 7
18: return

68. constant pool fun
void useManyNumeric() {
int i = 100;
int j = 1000000;
long l1 = 1;
long l2 = 0xffffffff;
double d = 2.2;
// ...do some calculations...
}
void useManyNumeric();
0: bipush 100
2: istore_1
3: ldc #2
// int 1000000
5: istore_2
6: lconst_1
7: lstore_3
8: ldc2_w #3
// long -1l
11: lstore 5
13: ldc2_w #5
// double 2.2d
16: dstore 7
18: return

69. constant pool fun
void useManyNumeric() {
int i = 100;
int j = 1000000;
long l1 = 1;
long l2 = 0xffffffff;
double d = 2.2;
// ...do some calculations...
}
void useManyNumeric();
0: bipush 100
2: istore_1
3: ldc #2
// int 1000000
5: istore_2
6: lconst_1
7: lstore_3
8: ldc2_w #3
// long -1l
11: lstore 5
13: ldc2_w #5
// double 2.2d
16: dstore 7
18: return

70. constant pool fun
void useManyNumeric() {
int i = 100;
int j = 1000000;
long l1 = 1;
long l2 = 0xffffffff;
double d = 2.2;
// ...do some calculations...
}
void useManyNumeric();
0: bipush 100
2: istore_1
3: ldc #2
// int 1000000
5: istore_2
6: lconst_1
7: lstore_3
8: ldc2_w #3
// long -1l
11: lstore 5
13: ldc2_w #5
// double 2.2d
16: dstore 7
18: return

71. constant pool fun
void useManyNumeric() {
int i = 100;
int j = 1000000;
long l1 = 1;
long l2 = 0xffffffff;
double d = 2.2;
// ...do some calculations...
}
void useManyNumeric();
0: bipush 100
2: istore_1
3: ldc #2
// int 1000000
5: istore_2
6: lconst_1
7: lstore_3
8: ldc2_w #3
// long -1l
11: lstore 5
13: ldc2_w #5
// double 2.2d
16: dstore 7
18: return

72. Constant Pool Fun
void useManyNumeric() {
int i = 100;
int j = 1000000;
long l1 = 1;
long l2 = 0xffffffff;
double d = 2.2;
// ...do some calculations...
}
void useManyNumeric();
0: bipush 100
2: istore_1
3: ldc #2
// int 1000000
5: istore_2
6: lconst_1
7: lstore_3
8: ldc2_w #3
// long -1l
11: lstore 5
13: ldc2_w #5
// double 2.2d
16: dstore 7
18: return

73. argument passing (virtual)
int addTwo(int i, int j) {
return i + j;
}

74. argument passing (virtual)
int addTwo(int i, int j) {
return i + j;
}
int addTwo(int, int);
stack=2, locals=3,
args_size=3
0: iload_1
1: iload_2
2: iadd
3: ireturn

75. argument passing (virtual)
int addTwo(int i, int j) {
return i + j;
}
int addTwo(int, int);
stack=2, locals=3,
args_size=3
0: iload_1
1: iload_2
2: iadd
3: ireturn

76. argument passing (virtual)
int addTwo(int i, int j) {
return i + j;
}
int addTwo(int, int);
stack=2, locals=3,
args_size=3
0: iload_1
1: iload_2
2: iadd
3: ireturn
StackLocals
this
i
j

77. argument passing (virtual)
int addTwo(int i, int j) {
return i + j;
}
int addTwo(int, int);
stack=2, locals=3,
args_size=3
0: iload_1
1: iload_2
2: iadd
3: ireturn
StackLocals
this
i
i
j

78. argument passing (virtual)
int addTwo(int i, int j) {
return i + j;
}
int addTwo(int, int);
stack=2, locals=3,
args_size=3
0: iload_1
1: iload_2
2: iadd
3: ireturn
StackLocals
this
i
i
j j

79. argument passing (virtual)
int addTwo(int i, int j) {
return i + j;
}
int addTwo(int, int);
stack=2, locals=3,
args_size=3
0: iload_1
1: iload_2
2: iadd
3: ireturn
StackLocals
this
i
i+j
j

80. argument passing (static)
static int addTwoStatic(int i, int j)
{
return i + j;
}

81. argument passing (static)
static int addTwoStatic(int i, int j)
{
return i + j;
}
static int
addTwoStatic(int, int);
flags: ACC_STATIC
Code:
stack=2, locals=2,
args_size=2
0: iload_0
1: iload_1
2: iadd
3: ireturn

82. argument passing (static)
static int addTwoStatic(int i, int j)
{
return i + j;
}
static int
addTwoStatic(int, int);
flags: ACC_STATIC
Code:
stack=2, locals=2,
args_size=2
0: iload_0
1: iload_1
2: iadd
3: ireturn

83. argument passing (static)
static int addTwoStatic(int i, int j)
{
return i + j;
}
static int
addTwoStatic(int, int);
flags: ACC_STATIC
Code:
stack=2, locals=2,
args_size=2
0: iload_0
1: iload_1
2: iadd
3: ireturn

84. argument passing (static)
static int addTwoStatic(int i, int j)
{
return i + j;
}
static int
addTwoStatic(int, int);
flags: ACC_STATIC
Code:
stack=2, locals=2,
args_size=2
0: iload_0
1: iload_1
2: iadd
3: ireturn
StackLocals
i
j
int 1
int 0

85. method call (virtual)
int add12and13() {
return addTwo(12, 13);
}
int add12and13();
Code:
stack=3, locals=1,
args_size=1
0: aload_0
1: bipush 12
3: bipush 13
5: invokevirtual #2
// Method addTwo:(II)I
8: ireturn
StackLocals
this

86. method call (virtual)
int add12and13() {
return addTwo(12, 13);
}
int add12and13();
Code:
stack=3, locals=1,
args_size=1
0: aload_0
1: bipush 12
3: bipush 13
5: invokevirtual #2
// Method addTwo:(II)I
8: ireturn
StackLocals
this this

87. method call (virtual)
int add12and13() {
return addTwo(12, 13);
}
int add12and13();
Code:
stack=3, locals=1,
args_size=1
0: aload_0
1: bipush 12
3: bipush 13
5: invokevirtual #2
// Method addTwo:(II)I
8: ireturn
StackLocals
this this
12

88. method call (virtual)
int add12and13() {
return addTwo(12, 13);
}
int add12and13();
Code:
stack=3, locals=1,
args_size=1
0: aload_0
1: bipush 12
3: bipush 13
5: invokevirtual #2
// Method addTwo:(II)I
8: ireturn
StackLocals
this this
12
13

89. method call (virtual)
int add12and13() {
return addTwo(12, 13);
}
int add12and13();
Code:
stack=3, locals=1,
args_size=1
0: aload_0
1: bipush 12
3: bipush 13
5: invokevirtual #2
// Method addTwo:(II)I
8: ireturn
StackLocals
this 25

90. method call (static)
int add12and13_static() {
return addTwoStatic(12, 13);
}
int add12and13_static();
Code:
stack=2, locals=1,
args_size=1
0: bipush 12
2: bipush 13
4: invokestatic #3
// Method
addTwoStatic:(II)I
7: ireturn
StackLocals
25

91. method call (static)
int add12and13_static() {
return addTwoStatic(12, 13);
}
int add12and13_static();
Code:
stack=2, locals=1,
args_size=1
0: bipush 12
2: bipush 13
4: invokestatic #3
// Method
addTwoStatic:(II)I
7: ireturn
StackLocals
12

92. method call (static)
int add12and13_static() {
return addTwoStatic(12, 13);
}
int add12and13_static();
Code:
stack=2, locals=1,
args_size=1
0: bipush 12
2: bipush 13
4: invokestatic #3
// Method
addTwoStatic:(II)I
7: ireturn
StackLocals
12
13

93. method call (static)
int add12and13_static() {
return addTwoStatic(12, 13);
}
int add12and13_static();
Code:
stack=2, locals=1,
args_size=1
0: bipush 12
2: bipush 13
4: invokestatic #3
// Method
addTwoStatic:(II)I
7: ireturn
StackLocals
25

94. method call (private)
class Near {
int it;
public int getItNear() {
return getIt();
}
private int getIt() {
return it;
}
}

95. method call (private)
class Near {
int it;
public int getItNear() {
return getIt();
}
private int getIt() {
return it;
}
}
public int getItNear();
stack=1, locals=1,
args_size=1
0: aload_0
1: invokespecial #3
// Method getIt:()I
4: ireturn

96. method call (super class)
class Far extends Near {
int getItFar() {
return super.getItNear();
}
}

97. method call (private)
class Far extends Near {
int getItFar() {
return super.getItNear();
}
}
int getItFar();
Code:
stack=1, locals=1,
args_size=1
0: aload_0
1: invokespecial #3
// Method
Examples3_7$Near.getItNaer:
()I
4: ireturn

98. types of calls
invokevirtual
invokestatic
invokeinterface
invokespecial
invokedynamic

99. types of calls
invokevirtual
invokestatic
invokeinterface
invokespecial
invokedynamic

100. types of calls

101. types of calls
invokevirtual
instance method
this pointer
virtual lookup

102. types of calls
invokevirtual
instance method
this pointer
virtual lookup
invokestatic
class method
no this pointer
static linking

103. types of calls
invokevirtual
instance method
this pointer
virtual lookup
invokestatic
class method
no this pointer
static linking
invokeinterface
interface method
this pointer
virtual lookup

104. types of calls
invokevirtual
instance method
this pointer
virtual lookup
invokestatic
class method
no this pointer
static linking
invokeinterface
interface method
this pointer
virtual lookup
invokespecial
Everything else
constructors
super class
private
this pointer
static linking

105. When two Objects love each other very
much…
Object create() {
return new Object();
}
StackLocals

106. When two Objects love each other very
much…
Object create() {
return new Object();
}
java.lang.Object create();
stack=2, locals=1,
args_size=1
0: new #2
// class java/lang/Object
3: dup
4: invokespecial #1
// Method
java/lang/Object."<init>":(
)V
7: areturn
StackLocals

107. When two Objects love each other very
much…
Object create() {
return new Object();
}
java.lang.Object create();
stack=2, locals=1,
args_size=1
0: new #2
// class java/lang/Object
3: dup
4: invokespecial #1
// Method
java/lang/Object."<init>":(
)V
7: areturn
StackLocals
baby

108. When two Objects love each other very
much…
Object create() {
return new Object();
}
java.lang.Object create();
stack=2, locals=1,
args_size=1
0: new #2
// class java/lang/Object
3: dup
4: invokespecial #1
// Method
java/lang/Object."<init>":(
)V
7: areturn
StackLocals
baby
baby

109. When two Objects love each other very
much…
Object create() {
return new Object();
}
java.lang.Object create();
stack=2, locals=1,
args_size=1
0: new #2
// class java/lang/Object
3: dup
4: invokespecial #1
// Method
java/lang/Object."<init>":(
)V
7: areturn
StackLocals
baby

110. field access
int i
void setIt(int value) {
i = value;
}
int getIt() {
return i;
}
StackLocals

111. field access (set)
int i
void setIt(int value) {
i = value;
}
int getIt() {
return i;
}
void setIt(int);
stack=2, locals=2,
args_size=2
0: aload_0
1: iload_1
2: putfield #6
// Field i:I
5: return
StackLocals

112. field access (set)
int i
void setIt(int value) {
i = value;
}
int getIt() {
return i;
}
void setIt(int);
stack=2, locals=2,
args_size=2
0: aload_0
1: iload_1
2: putfield #6
// Field i:I
5: return
StackLocals
this

113. field access (set)
int i
void setIt(int value) {
i = value;
}
int getIt() {
return i;
}
void setIt(int);
stack=2, locals=2,
args_size=2
0: aload_0
1: iload_1
2: putfield #6
// Field i:I
5: return
StackLocals
this
value

114. field access (set)
int i
void setIt(int value) {
i = value;
}
int getIt() {
return i;
}
void setIt(int);
stack=2, locals=2,
args_size=2
0: aload_0
1: iload_1
2: putfield #6
// Field i:I
5: return
StackLocals

115. field access (get)
int i
void setIt(int value) {
i = value;
}
int getIt() {
return i;
}
int getIt();
stack=1, locals=1,
args_size=1
0: aload_0
1: getfield #6
// Field i:I
4: ireturn
StackLocals

116. array opcodes
newarray (primitive type)
anewarray
multianewarray
Tastore (e.g. iastore)
Taload (e.g. faload)

117. switch statement (table)
int chooseNear(int i) {
switch (i) {
case 0: return 0;
case 1: return 1;
case 2: return 2;
default: return -1;
}
}

118. switch statement (table)
int chooseNear(int i) {
switch (i) {
case 0: return 0;
case 1: return 1;
case 2: return 2;
default: return -1;
}
}
int chooseNear(int);
0: iload_1
1: tableswitch { // 0 to 2
0: 28
1: 30
2: 32
default: 34
}
28: iconst_0
29: ireturn
30: iconst_1
31: ireturn
32: iconst_2
33: ireturn
34: iconst_m1
35: ireturn

119. switch statement (sparse)
int chooseFar(int i) {
switch (i) {
case -100: return -1;
case 0: return 0;
case 100: return 1;
default: return -1;
}
}

120. switch statement (sparse)
int chooseFar(int i) {
switch (i) {
case -100: return -1;
case 0: return 0;
case 100: return 1;
default: return -1;
}
}
int chooseFar(int);
0: iload_1
1: lookupswitch { // 3
-100: 36
0: 38
100: 40
default: 42
}
36: iconst_m1
37: ireturn
38: iconst_0
39: ireturn
40: iconst_1
41: ireturn
42: iconst_m1
43: ireturn

121. untyped stack operations
pop
pop2
dup
dup2
dup_x1
dup2_x1
dup_x2
dup2_x2
swap

122. Exceptions
void catchOne();
stack=2, locals=2, args_size=1
0: aload_0
1: invokevirtual #4 // Method tryItOut:()V
4: goto 13
7: astore_1
8: aload_0
9: aload_1
10: invokevirtual #5
// Method handleExc:(Ljava/lang/Exception;)V
13: return
Exception table:
from to target type
0 4 7 Class TestExc

123. Exceptions
void catchOne() {
try {
tryItOut();
} catch (TestExc e) {
handleExc(e);
}
}

124. Exceptions
void catchOne();
stack=2, locals=2, args_size=1
0: aload_0
1: invokevirtual #4 // Method tryItOut:()V
4: goto 13
7: astore_1
8: aload_0
9: aload_1
10: invokevirtual #5
// Method handleExc:(Ljava/lang/Exception;)V
13: return
Exception table:
from to target type
0 4 7 Class TestExc

125. Exceptions
void catchOne();
stack=2, locals=2, args_size=1
0: aload_0
1: invokevirtual #4 // Method tryItOut:()V
4: goto 13
7: astore_1
8: aload_0
9: aload_1
10: invokevirtual #5
// Method handleExc:(Ljava/lang/Exception;)V
13: return
Exception table:
from to target type
0 4 7 Class TestExc

126. Exceptions
void catchOne();
stack=2, locals=2, args_size=1
0: aload_0
1: invokevirtual #4 // Method tryItOut:()V
4: goto 13
7: astore_1
8: aload_0
9: aload_1
10: invokevirtual #5
// Method handleExc:(Ljava/lang/Exception;)V
13: return
Exception table:
from to target type
0 4 7 Class TestExc

127. about finally
jsr / ret removed in jdk7 (cass file ver. 51)
now finally block code is just copied to each possible exit point

128. Q&A

129. Thank You!!!

130. Session Survey
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131. The preceding is intended to outline our general product direction. It is intended for information purposes
only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code,
or functionality, and should not be relied upon in making purchasing decisions. The development,
release, timing, and pricing of any features or functionality described for Oracle’s products may change
and remains at the sole discretion of Oracle Corporation.
Statements in this presentation relating to Oracle’s future plans, expectations, beliefs, intentions and
prospects are “forward-looking statements” and are subject to material risks and uncertainties. A detailed
discussion of these factors and other risks that affect our business is contained in Oracle’s Securities and
Exchange Commission (SEC) filings, including our most recent reports on Form 10-K and Form 10-Q
under the heading “Risk Factors.” These filings are available on the SEC’s website or on Oracle’s website
at http://www.oracle.com/investor. All information in this presentation is current as of September 2019
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