java - Avoiding getfield opcode

Question

In Java's String class, the trim method contains this:

int off = offset;      /* avoid getfield opcode */
char[] val = value;    /* avoid getfield opcode */

I'm a bit puzzled by the comment "avoid getfield opcode"...

What does this mean? (I take it this avoids the use of getfield in the bytecode but why is this a Good Thing [TM]?)

Is it to prevent object creation in case trim doesn't do anything (and hence this is returned) or?

Answer 1

My guess is that the point is to copy the values into local variables once, to avoid having to fetch the field value repeatedly from the heap for each iteration of the loop in the next few lines.

Of course, that begs the question as to why the same comment hasn't been applied on the "len" local variable. (I'd also expect the JIT to avoid refetching anyway, especially as the variables are final.)