Java程序辅导

J. Xue✬
✫
✩
✪
COMP3131/9102: Programming Languages and Compilers
Jingling Xue
School of Computer Science and Engineering
The University of New South Wales
Sydney, NSW 2052, Australia
http://www.cse.unsw.edu.au/~cs3131
http://www.cse.unsw.edu.au/~cs9102
Copyright @2018, Jingling Xue
COMP3131/9102 Page 577 May 20, 2018
J. Xue✬
✫
✩
✪
Bonus Assignment
• Deadline: 3 June 2018
• Worth: 5 marks
COMP3131/9102 Page 578 May 20, 2018
J. Xue✬
✫
✩
✪
Timetable
• Lectures:
Week 12: this lecture
Week 13: no lecture (Working on Assn 5)
• Tutorials:
Week 12: on
Week 13: no tutorial
COMP3131/9102 Page 579 May 20, 2018
J. Xue✬
✫
✩
✪
Lecture 11: Java Class File Format & Runtime Areas
1. Timetable
2. Class file format (Sun’s JVM Spec Book)
3. Runtime areas (JVM Spec & Bill Venners’ Inside the JVM book)
4. Java bytecode verification
5. Revision
6. PhD topics
7. Final exam
COMP3131/9102 Page 580 May 20, 2018
J. Xue✬
✫
✩
✪
Lvalue v.s. Rvalue
• Question: are the following legal in C, Java and C++?
++i = 1; i++ = 1; (i=j) = 1;
• Consider
int i = 5;
i = i + 1;
add the rvalue 5 and 1 and
store 6 into lvalue 2000
2000
memory
5
rvalue
lvalue
(address)
COMP3131/9102 Page 581 May 20, 2018
J. Xue✬
✫
✩
✪
Example 1: Test.java
class Test {
public static void main(String argv[]) { }
}
COMP3131/9102 Page 582 May 20, 2018
J. Xue✬
✫
✩
✪
Example 1: Java Class File (Output of od -An -tx1 Test.class)
ca fe ba be 00 03 00 2d 00 0f 07 00 0b 07 00 0d
0a 00 02 00 04 0c 00 07 00 05 01 00 03 28 29 56
01 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f
53 74 72 69 6e 67 3b 29 56 01 00 06 3c 69 6e 69
74 3e 01 00 04 43 6f 64 65 01 00 0f 4c 69 6e 65
4e 75 6d 62 65 72 54 61 62 6c 65 01 00 0a 53 6f
75 72 63 65 46 69 6c 65 01 00 04 54 65 73 74 01
00 09 54 65 73 74 2e 6a 61 76 61 01 00 10 6a 61
76 61 2f 6c 61 6e 67 2f 4f 62 6a 65 63 74 01 00
04 6d 61 69 6e 00 20 00 01 00 02 00 00 00 00 00
02 00 00 00 07 00 05 00 01 00 08 00 00 00 1d 00
01 00 01 00 00 00 05 2a b7 00 03 b1 00 00 00 01
00 09 00 00 00 06 00 01 00 00 00 01 00 09 00 0e
00 06 00 01 00 08 00 00 00 19 00 00 00 01 00 00
00 01 b1 00 00 00 01 00 09 00 00 00 06 00 01 00
00 00 03 00 01 00 0a 00 00 00 02 00 0c
• The classfile format defined in the Sun’s JVM spec book
• BCEL’s listclass useful for understanding the constant pool
• Generated using Java 45.3
COMP3131/9102 Page 583 May 20, 2018
J. Xue✬
✫
✩
✪
Example 1: Test.class Annotated
ca fe ba be magic
00 03 minor version
00 2d major version
00 0f constant pool count
-------------------- constant pool table --------------------------
07 00 0b
07 00 0d
0a 00 02 00 04
0c 00 07 00 05
01 00 03 28 29 56
01 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 74 72 69 6e 67 3b 29 56
01 00 06 3c 69 6e 69 74 3e
01 00 04 43 6f 64 65
01 00 0f 4c 69 6e 65 4e 75 6d 62 65 72 54 61 62 6c 65
01 00 0a 53 6f 75 72 63 65 46 69 6c 65
01 00 04 54 65 73 74
01 00 09 54 65 73 74 2e 6a 61 76 61
01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 4f 62 6a 65 63 74
01 00 04 6d 61 69 6e
-------------------- end of constant pool table --------------------------
00 20 access_flags
00 01 this_class
00 02 super_class
00 00 interfaces_count
COMP3131/9102 Page 584 May 20, 2018
J. Xue✬
✫
✩
✪
00 00 fields_count
00 02 methods_count
------------------  ---------------------------------------
00 00 access_flags
00 07 name_index
00 05 desc_index
00 01 attr_count
00 08 attr_name_index
00 00 00 1d attr_length
00 01 max_stack
00 01 max_locals
00 00 00 05 code_length
2a b7 00 03 b1 code
00 00 exception_table_length
00 01 attr_count
00 09 LineNumberTable
00 00 00 06 attr_length
00 01 line_number_table_length
00 00 start_pc
00 01 line_number
------------------ end of  ---------------------------------
------------------------------ main -----------------------------
00 09 access_flags
00 0e name_index
00 06 desc_index
00 01 attr_count
00 08 attr_name_index
00 00 00 19 attr_length
00 00 max_stack
00 01 max_locals
00 00 00 01 code_length
COMP3131/9102 Page 585 May 20, 2018
J. Xue✬
✫
✩
✪
b1 code
00 00 exception_table_length
00 01 attr_count
00 09 attr_name_index
00 00 00 06 attr_length
00 01 line_number_table_length
00 00 start_pc
00 03 line_number
------------------------------ end of main ------------------------
00 01 attr_count
00 0a attr_name_index
00 00 00 02 attr_length
00 0c sourcefile_index
COMP3131/9102 Page 586 May 20, 2018
J. Xue✬
✫
✩
✪
Example 1: Test.class Annotated (java listclass -code
-constants Test.class, where listclass is from BCEL)
class Test extends java.lang.Object
filename Test.class
compiled from Test.java
compiler version 45.3
access flags 32
constant pool 15 entries
ACC_SUPER flag true
Attribute(s):
SourceFile(Test.java)
2 methods:
void ()
public static void main(String[])
1)CONSTANT_Class[7](name_index = 11)
2)CONSTANT_Class[7](name_index = 13)
3)CONSTANT_Methodref[10](class_index = 2, name_and_type_index = 4)
4)CONSTANT_NameAndType[12](name_index = 7, signature_index = 5)
5)CONSTANT_utf8[1]("()V")
6)CONSTANT_Utf8[1]("([Ljava/lang/String;)V")
7)CONSTANT_Utf8[1]("")
8)CONSTANT_Utf8[1]("Code")
9)CONSTANT_Utf8[1]("LineNumberTable")
10)CONSTANT_Utf8[1]("SourceFile")
COMP3131/9102 Page 587 May 20, 2018
J. Xue✬
✫
✩
✪
11)CONSTANT_Utf8[1]("Test")
12)CONSTANT_Utf8[1]("Test.java")
13)CONSTANT_Utf8[1]("java/lang/Object")
14)CONSTANT_Utf8[1]("main")
void ()
Code(max_stack = 1, max_locals = 1, code_length = 5)
0: aload_0
1: invokespecial java.lang.Object. ()V (3)
4: return
Attribute(s) =
LineNumber(0, 1)
public static void main(String[])
Code(max_stack = 0, max_locals = 1, code_length = 1)
0: return
Attribute(s) =
LineNumber(0, 3)
COMP3131/9102 Page 588 May 20, 2018
J. Xue✬
✫
✩
✪
Java Runtime Areas
1. pc registers
2. Java stacks (due to multi-threading)
• Local variables
• Operand stack
• Frame data
– pointer to constant pool
– information about method return
– · · ·
3. Method Area
4. Heap
All JVM diagrams are from Bill Venner’s Inside the JVM book
COMP3131/9102 Page 589 May 20, 2018
J. Xue✬
✫
✩
✪
Internal Architecture of JVM
COMP3131/9102 Page 590 May 20, 2018
J. Xue✬
✫
✩
✪
Method Area and Heap
• Arrays are objects
COMP3131/9102 Page 591 May 20, 2018
J. Xue✬
✫
✩
✪
Java Stacks – One Per Thread
COMP3131/9102 Page 592 May 20, 2018
J. Xue✬
✫
✩
✪
Stack Frame
• A new stack frame is created for every method invocation
• Stack frame consists of:
– Local variables (lectures 9 & 10)
– Frame data
– Operand stack (lectures 9 & 10)
COMP3131/9102 Page 593 May 20, 2018
J. Xue✬
✫
✩
✪
One Possible Implementation of a Java Frame
Local
Variables
Frame
Data
Operand
Stack
COMP3131/9102 Page 594 May 20, 2018
J. Xue✬
✫
✩
✪
Example 2: gcd.vc
int i = 5;
int j = 2;
// find the greatest common divisor of two integers
int gcd(int a, int b) {
if (b == 0)
return a;
else
return gcd(b, a - (a/b) *b);
}
int main() {
putIntLn(gcd(i, j));
}
COMP3131/9102 Page 595 May 20, 2018
J. Xue✬
✫
✩
✪
Example 2: gcd.java
import VC.lang.System;
public class gcd {
static int i = 5;
static int j = 2;
public gcd() { }
int gcd(int a, int b) {
if (b == 0)
return a;
else
return gcd(b, a - (a/b) *b);
}
public static void main(String argv[]) {
gcd vc$;
vc$ = new gcd();
System.putIntLn(vc$.gcd(i, j));
}
}
COMP3131/9102 Page 596 May 20, 2018
J. Xue✬
✫
✩
✪
Example 2: gcd.j
.class public gcd
.super java/lang/Object
.field static i I
.field static j I
; standard class static initializer
.method static ()V
iconst_5
putstatic gcd/i I
iconst_2
putstatic gcd/j I
; set limits used by this method
.limit locals 0
.limit stack 1
return
.end method
; standard constructor initializer
.method public ()V
.limit stack 1
.limit locals 1
aload_0
invokespecial java/lang/Object/()V
return
.end method
.method gcd(II)I
.limit stack 5
.limit locals 3
.var 0 is this Lgcd; from Label1 to Label2
.var 1 is a I from Label1 to Label2
.var 2 is b I from Label1 to Label2
COMP3131/9102 Page 597 May 20, 2018
J. Xue✬
✫
✩
✪
Label1:
.line 10
iload_2
ifne Label0
.line 11
iload_1
ireturn
Label0:
.line 13
aload_0
iload_2
iload_1
iload_1
iload_2
idiv
iload_2
imul
isub
invokevirtual gcd/gcd(II)I
Label2:
ireturn
.end method
.method public static main([Ljava/lang/String;)V
L0:
.var 0 is argv [Ljava/lang/String; from L0 to L1
.var 1 is vc$ Lgcd; from L0 to L1
new gcd
dup
invokenonvirtual gcd/()V
astore_1
aload_1
getstatic gcd/i I
getstatic gcd/j I
invokevirtual gcd/gcd(II)I
invokestatic VC/lang/System/putIntLn(I)V
L1:
COMP3131/9102 Page 598 May 20, 2018
J. Xue✬
✫
✩
✪
; The following return inserted by the VC compiler
return
; set limits used by this method
.limit locals 2
.limit stack 3
.end method
COMP3131/9102 Page 599 May 20, 2018
J. Xue✬
✫
✩
✪
Reading
• Class file format (Sun’s JVM Spec Book)
• Runtime areas (JVM Spec & Bill Venners’ Inside the JVM
book)
COMP3131/9102 Page 600 May 20, 2018
J. Xue✬
✫
✩
✪
Lecture 11: Java Class File Format & Runtime Areas
1. Timetable
√
2. Class file format (Sun’s JVM Spec Book)
√
3. Runtime areas (JVM Spec & Bill Venners’ Inside the JVM book)
√
4. Java bytecode verification
5. Revision
6. PhD topics
7. Final exam
COMP3131/9102 Page 601 May 20, 2018
J. Xue✬
✫
✩
✪
ByteCode Verification
• Loop
while (true) 1;
• Bytecode:
iconst_1
pop
• Removing pop causes a Java.VerifyError:
Exception in thread "main" java.lang.VerifyError: (class: x,
method: foo signature: (V) Inconsistent stack height 1 != 0)
• JVM Spec:
If an instruction can be executed along several different execution paths, the
operand stack must have the same depth (2.6.2) prior to the execution of the
instruction, regardless of the path taken.
https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#
jvms-4.10.1.4
COMP3131/9102 Page 602 May 20, 2018
J. Xue✬
✫
✩
✪
The VC Compiler
Source Code (Test.vc)
Assignment 1: Scanner
Assignment 2a & 2b: Parser
Assignment 3: Semantic Analyser
Assignment 4: Code Generator
Jasmin Assembly Code (Test.j)
Jasmin Assembler
Java Virtual Machine
Results
V
C
.
l
a
n
g
.
S
y
s
t
e
m
.
c
l
a
s
s
Tokens
AST
Decorated AST
Java Byte Code (Test.class)
COMP3131/9102 Page 603 May 20, 2018
J. Xue✬
✫
✩
✪
Scanning
• Theory:
– Regular expressions (i.e., regular grammars)
– Finite automata (DFAs and NFAs)
• Writing a scanner
– Hand coding
– Scanner generator (JLex and JavaCC)
COMP3131/9102 Page 604 May 20, 2018
J. Xue✬
✫
✩
✪
Thompson’s Construction (Cont’d): Slide 79
N(r)
N(s)
S A
ǫ
ǫ
ǫ
ǫ
RE r|s : start
S N(r) AN(s)
start
RE rs :
N(r)S A
ǫ ǫ
ǫ
ǫ
start
RE r∗ :
RE (r) : N((r)) is the same as N(r)
COMP3131/9102 Page 605 May 20, 2018
J. Xue✬
✫
✩
✪
False RE r∗ Rule
S N(r) T
ǫ
ǫ
start
RE r∗ :
• The FA constructed using this rule may not be correct.
• Try (a∗b)∗!
• The ǫ edges in Thompson’s construction ensure that the
construction is correct, and are removed when the NFA is
converted to a DFA
COMP3131/9102 Page 606 May 20, 2018
J. Xue✬
✫
✩
✪
Parsing
• Theory:
• Context-free grammars
• First, Follow and Select sets
• Writing a parser
• Recursive-descent
• Table-driven LL(1)
• Parser generators (JavaCUP and JavaCC)
LR(k) not covered this year
COMP3131/9102 Page 607 May 20, 2018
J. Xue✬
✫
✩
✪
Context-Sensitive Analysis
• Theory:
• Attribute grammars
• Evaluation of attributes
• Scoping
• Type rules
• Writing a context-sensitive analyser
• Identification: Relate the use of an identifier to its
declaration
• Type Checking: Enforce the language’s type rules
COMP3131/9102 Page 608 May 20, 2018
J. Xue✬
✫
✩
✪
Code Generation
• Theory:
• Syntax-directed translation
• Code templates
• Writing a code generator
• JVM
• Jasmin assembly language
COMP3131/9102 Page 609 May 20, 2018
J. Xue✬
✫
✩
✪
PhD Projects
• Some current PhD projects:
– Compiler techniques for heterogeneous architectures (CPUs +
TPUs/GPUs/FPGAs)
– Concurrent programming (e.g., programming model and OO)
– Program analysis for safety and security
• PhD topics
– Languages and compilers for multicore computing (e.g., GPUs)
– Language safety and security
– Compilers for asymmetrical multicores
– Security analysis of Android apps
– Static and dynamic analysis for bug detection
COMP3131/9102 Page 610 May 20, 2018
J. Xue✬
✫
✩
✪
Final Exam
• 2 hours, closed
• 6 questions
• The papers and solutions for 2000 – 2003 available:
1. Login to a CSE computer
2. Type:
cp ~cs3131/Exams/past-exams.zip your-directory
COMP3131/9102 Page 611 May 20, 2018
J. Xue✬
✫
✩
✪
Remember to Complete
myExperience Survey for
COMP3131/9102
Good luck with your studies!
COMP3131/9102 Page 612 May 20, 2018