Assembly Language for Beginners

4.1. JAVA

50: ldc #12 // String September

52: aastore

53: dup

54: bipush 9

56: ldc #13 // String October

58: aastore

59: dup

60: bipush 10

62: ldc #14 // String November

64: aastore

65: dup

66: bipush 11

68: ldc #15 // String December

70: aastore

71: putstatic #2 // Field months:[Ljava/lang/String;

74: return

anewarraycreates a new array ofreferences(henceaprefix).

The object’s type is defined in theanewarray’s operand, it is the
“java/lang/String” string.

Thebipush 12beforeanewarraysets the array’s size.

We see here a new instruction for us:dup.

It’s a standard instruction in stack computers (including the Forth programming language) which just

duplicates the value atTOS.

By the way, FPU 80x87 is also a stack computer and it has similar instruction –FDUP.

It is used here to duplicate areferenceto an array, because theaastoreinstruction pops thereference

to array from the stack, but subsequentaastorewill need it again.

The Java compiler concluded that it’s better to generate adupinstead of generating agetstaticinstruc-

tion before each array store operation (i.e., 11 times).

aastoreputs areference(to string) into the array at an index which is taken fromTOS.

Finally,putstaticputsreferenceto the newly created array into the second field of our object, i.e.,

monthsfield.

Variadic functions

Variadic functions actually use arrays:

public static void f(int... values)

{

for (int i=0; i<values.length; i++)

System.out.println(values[i]);

}

public static void main(String[] args)

{

f (1,2,3,4,5);

}

public static void f(int...);

flags: ACC_PUBLIC, ACC_STATIC, ACC_VARARGS

Code:

stack=3, locals=2, args_size=1

0: iconst_0

1: istore_1

2: iload_1

3: aload_0

4: arraylength

5: if_icmpge 23

8: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;

11: aload_0

12: iload_1

13: iaload