How does byte[] get compiled in the class file?

[ying lam]

Hi,

If I have a method which has a byte[] as its variable,

public void f1() {
byte[] matchBytes = {0x50, 0x4e, 0x47};
...
}

like this, how does that compile into a class file?
When I open the compiled class file, and search for '0x50' '0x4e' '0x47', nothing is found.

And what if I have a class which has static constants attribute of byte[] matchBytes = {0x50, 0x4e, 0x47}; how does that compile into a class file?

Thank you.

[Ernest Friedman-Hill]

It's rather unsettling, actually. Array initializers aren't compiled into a block of data that can be copied directly into an array; they're compiled into a stream of executable code that sets the elements of the array one at a time!

   5:   iconst_3      // array size
   6:   newarray byte // alloc array
   8:   dup           // copy array reference
   9:   iconst_0      // zeroth element
   10:  bipush  80    // 0x50 in decimal
   12:  bastore       // store in array
   13:  dup           // copy array ref
   14:  iconst_1      // oneth element
   15:  bipush  78    // 0x4e
   17:  bastore       // store
   18:  dup           
   19:  iconst_2      // element 2
   20:  bipush  71    // 0x47
   22:  bastore       
   23:  putfield #2   // store array ref in member variable

You can disassemble classes like this using the "javap" tool: "javap -c Foo" shows you the bytecode for class Foo.

[ying lam]

Thanks.