Re: Do any Java compilers or JVMs optimize getter method calls?

David Karr <>
Thu, 3 Sep 2009 16:32:57 -0700 (PDT)
On Sep 3, 3:56 pm, Lew <> wrote:

david.karr wrote:

I prefer to reference instance variables through getters, as opposed
to direct access to them. However, there's "obviously" going to be a
small time penalty for that. I did some timings in Eclipse, and I
found direct reads were a tiny fraction faster than through the getter
call (no surprise), and the difference between the setter and a direct
write was even smaller (I tested 100000000 iterations, adding up the
nanosecond intervals of each type of access).

I'm wondering whether there are any compiler/JVM combinations that
optimize getter calls to be the same as a direct access? I can see
from the bytecode in Eclipse that there is no optimization at that
level, but I don't know if the JVM will do any optimization in some
cases. It didn't appear to do it in Eclipse, but I don't know if other
JVMs would act differently.

You cannot tell optimization from the bytecode, because optimization happ=


in the JVM.

Yes, I know, I was just pointing out the bytecode wasn't already pre-

Doesn't Eclipse use the JVM installed on your system? What JVM is inst=


on your system?

Yes. I've tested with Sun's 1.5.0_19, 1.6.0_14, and 1.6.0_16.

What options are you passing to the JVM now?

The most significant optimizations occur with the "-server" option to the
"java" command (or equivalent). Others are possible. They are docum=

ented on and elsewhere.

I wasn't using "-server" before, but I am now. That's a useful

Methods declared as 'final' tend to be inlined and run faster than method=

s not

so qualified.

When running your benchmarks, let the loop run a bunch of times before yo=


start timing. That lets the Hotspot compiler analyze the run and figur=

e out

what to optimize.

I'm also using both of these strategies. I'm running 100000000 timed
iterations, so I doubt the warm-up loop is necessary, but I'm doing
that anyway.

My measurements show very tiny differences (perhaps .02% total
difference over all 100000000 iterations). In fact, emphasizing the
fact that this isn't statistically significant, I saw several runs
where the "direct" test was slightly slower than the "getter" test.

If it matters, following this is my test class.
package timings;

public class Timings {

    private String foo;

    final public String getFoo() {return foo;}
    final public void setFoo(String foo) { = foo;}

    public static void main(String[] args) {
        Timings timings = new Timings(args);

    public Timings(String[] args) {}

    private void go() {

        // warmup loop.
        for (int ctr = 0; ctr < 1000; ++ ctr) {
            setFoo(ctr + "");
   = + "";

        int iters = 10000000;

        long totalns;

        totalns = 0;
        for (int ctr = 0; ctr < iters; ++ ctr) {
            setFoo(ctr + "");
            long startTime = System.nanoTime();
            String val = getFoo();
            totalns += (System.nanoTime() - startTime);
        System.out.println("getter[" + totalns + "]");

        totalns = 0;
        for (int ctr = 0; ctr < iters; ++ ctr) {
            setFoo(ctr + "");
            long startTime = System.nanoTime();
            String val =;
            totalns += (System.nanoTime() - startTime);
        System.out.println("direct[" + totalns + "]");

        totalns = 0;
        for (int ctr = 0; ctr < iters; ++ ctr) {
            long startTime = System.nanoTime();
            setFoo(ctr + "");
            totalns += (System.nanoTime() - startTime);
        System.out.println("setter[" + totalns + "]");

        totalns = 0;
        for (int ctr = 0; ctr < iters; ++ ctr) {
            long startTime = System.nanoTime();
   = ctr + "";
            totalns += (System.nanoTime() - startTime);
        System.out.println("direct[" + totalns + "]");

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