Final attributes and local variables - performance ??

Question

Hi all,
I and a colleague have done some performance testing regarding the use of final attributes and final local variables, e.g.
with final:
public class MyClass {
  private final int i;
  public final void myMethod() {
    final int j = 5;
    // do something with i and j
}vs. non-final:
public class MyClass {
  private int i;
  public final void myMethod() {
    int j = 5;
    // do something with i and j
}I couldn't find any speed differences in a small test program, but my colleague did so in his application. Who is right ??
Still, I will have do some formal testing next week and I will post the results.
I'd prefer the version using final anyway because I find it better readable, but the issue I am having is whether I'll spend 2-3 days going through the program making everything final or not.

Answer 1

I made some tests with final arguments to a method: I could not find any difference between final and non-final arguments. code is posted below
import java.io.*;
import java.net.*;
import java.rmi.*;
import java.util.*;
import javax.ejb.*;
import javax.naming.*;
import javax.rmi.PortableRemoteObject;
import junit.framework.*;
import junit.extensions.*;
public final class FinalVariablesTest extends TestCase /* from junit */ {
     * Constructors
    public FinalVariablesTest(String name) {
        super(name);
     * helper methods/classes
    protected void setUp() throws Exception {
        super.setUp();
    protected void tearDown() throws Exception {
        super.tearDown();
     * Test Suite
    public static void main(String[] args) {
     junit.textui.TestRunner.run(suite());
    public static Test suite() {
        return new TestSuite(FinalVariablesTest.class);
     * Test Cases
    /** tests the effect of passing an (final or non-final) int parameter
     to a method which uses the variable in a for loop.
     <p>
     Linux System:
     cat /proc/cpuinfo
     processor       : 0
     vendor_id       : GenuineIntel
     cpu family      : 6
     model           : 8
     model name      : Pentium III (Coppermine)
     stepping        : 1
     cpu MHz         : 501.146
     cache size      : 256 KB
     fdiv_bug        : no
     hlt_bug         : no
     sep_bug         : no
     f00f_bug        : no
     coma_bug        : no
     fpu             : yes
     fpu_exception   : yes
     cpuid level     : 2
     wp              : yes
     flags           : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr xmm
     bogomips        : 999.42
     </pre>
     <p>
     Results:
     <pre>
     java version "1.4.0"
     Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-b92)
     Java HotSpot(TM) Client VM (build 1.4.0-b92, mixed mode)
     final     non-final
     498     500
     491     494
     491     493
     491     494
     534     494
     492     494
     491     494
     492     493
     491     494
     495     494
     4966     4944 (Totals)
     </pre>
    public final void testIntParametersToForLoop() {
     final int RUNS = 10;
     final int INNER = 1000000;
     final int OUTER = 10;
     System.out.println("-----------------------");
     System.out.println("testIntParametersToForLoop");
     for(int i=0; i<RUNS; i++) {
         outerFinalIntParametersToForLoop(INNER, OUTER);
         outerNonFinalIntParametersToForLoop(INNER, OUTER);
    private final void outerFinalIntParametersToForLoop(final int INNER,
                                   final int OUTER) {
     // with final var in for loop
     long start0 = System.currentTimeMillis();
     for(int i=0; i<OUTER; i++) {
         innerFinalIntParametersToForLoop(INNER * i);
     long end0 = System.currentTimeMillis();
     System.out.println("      final:       " +
                  ( end0 - start0 ) + " milliseconds");
    private final void outerNonFinalIntParametersToForLoop(final int INNER,
                                      final int OUTER) {
     // with non-final var in for loop
     long start1 = System.currentTimeMillis();
     for(int i=0; i<OUTER; i++) {
         innerNonFinalIntParametersToForLoop(INNER * i);
     long end1 = System.currentTimeMillis();
     System.out.println("  non final: " +
                  ( end1 - start1 ) + "       milliseconds");
    private final void innerFinalIntParametersToForLoop(final int INNER) {
     for(int i=0; i<INNER; i++) {
         int testVar = i * INNER;
    private final void innerNonFinalIntParametersToForLoop(int loops) {
     for(int i=0; i<loops; i++) {
         int testVar = i * loops;