Notes: Tuesday 4 November 2003

Schedule

• Tuesday, 11 November: PS5 Part 2
• Tuesday, 18 November: No class
• Tuesday, 25 November: PS6 Due
• Tuesday, 2 December: Exam 2 Out
• Friday, 5 December: Exam 2

Selected JavaVM Instructions

Opcode	Mnemonic	Description
0	nop	Does nothing
1	aconst_null	Push null on the stack
3	iconst_0	Push int 0 on the stack
4	iconst_1	Push int 1 on the stack
8	iconst_5	Push int 5 on the stack
9	lconst_0	Push long 0 on the stack
...	...	...
21	iload varnum	Push the int value in local variable varnum on the stack
22	lload varnum	Push the long value in local variable varnum on the stack
23	fload varnum	Push the float value in local variable varnum on the stack
24	dload varnum	Push the double value in local variable varnum on the stack
25	aload varnum	Push the object reference in local variable varnum on the stack
26	iload_0	Push the int value in local variable 0 on the stack
27	iload_1	Push the int value in local variable 1 on the stack
	...	...	...
45	aload_3	Push the object reference in local variable 3 on the stack
...	...	...
54	istore varnum	Store the int value at the top of the stack in local variable varnum and pop it from stack
58	astore varnum	Store the object reference at the top of the stack in local variable varnum and pop it from stack
...	...	...
45	aload_3	Push the object reference in local variable 3 on the stack
	...	...	...
87	pop	Pops the top (single word) off the stack
88	pop2	Pops the top two words off the stack
89	dup	Pops the top of the stack, and pushes that value twice
...	...	...
96	iadd	Pops two ints off the stack, and pushes their sum
97	ladd	Pops two longs off the stack, and pushes their sum
104	imul	Pops two ints off the stack, and pushes their product
116	ineg	Pops an int off the stack, and pushes its negation
153	ifeq label	Pops an int off the stack, if it is zero, jump to label
154	ifne label	Pops an int off the stack, if it is not zero, jump to label
165	if_acmpeq label	Pops two object references off the stack, if they are equal (same object), jump to label
167	goto label	Causes execution to jump to label
172	ireturn	Pops an int off the stack, and pushes it onto the caller's stack. Discards all other items on this method's stack. Causes execution to contion at the call site.
180	getfield field	Pops an object reference from the stack, and pushes the value of the specified field of that object on the stack
181	putfield field	Pops a value and an object reference from the stack, and store the value in the specified field of that object
182	invokevirtual method	Pops an object reference from the stack, and invokes the specified method on that object; pops the parameters from the stack, and stores them in local variables
183	invokespecial method	Pops an object reference from the stack, and invokes the specified method on that object; pops the parameters from the stack, and stores them in local variables. (Used for constructors, private methods and super invocations.)
184	invokestatic method	Invokes the specified static method; pops the parameters from the stack, and stores them in local variables
187	new class	Pushes an object reference to a new object of type class
188	newarray type	Pops an integer off the stack, and pushes a reference to a new array of the specified type and the size of the popped integer
...	...	...
201	jsr_w label	Jump to a subroutine using a wide offset (useful for exception handling)

For a complete description of all the JavaVM instructions, see The Java^TM Virtual Machine Specification.

To examine the byte codes the compiler produces for a class:

1. Start a DOS shell by selecting "Run" from the Start menu and entering "cmd"
2. cd to the directory containing the class file
3. java -p classname

Method void main(java.lang.String[])
   0 iconst_2
   1 istore_1
   2 iconst_3
   3 istore_2
   4 iload_1
   5 iload_2
   6 iadd
   7 istore_3
   8 getstatic #2 <Field java.io.PrintStream err>
  11 new #3 <Class java.lang.StringBuffer>
  14 dup
  15 invokespecial #4 <Method java.lang.StringBuffer()>
  18 ldc #5 <String "c: ">
  20 invokevirtual #6 <Method java.lang.StringBuffer
   append(java.lang.String)>
  23 iload_3
  24 invokevirtual #7 <Method java.lang.StringBuffer append(int)>
  27 invokevirtual #8 <Method java.lang.String toString()>
  30 invokevirtual #9 <Method void println(java.lang.String)>
  33 return

University of Virginia Department of Computer Science CS 201J: Engineering Software

Sponsored by the National Science Foundation

cs201j-staff@cs.virginia.edu