Is it really effective to use the final keyword inline compiler optimization in Java?

(inkfish original, reprint please indicate the source: http://blog.csdn.net/inkfish/)

In order to seek the performance optimization of Java code, search from the internet to use final keyword compile-time inline optimization method, but really effective. The actual test found that not necessarily, even the performance impact of the huge, eventually abandoned the idea of using final optimization.

Test environment: Windows XP sp2,jdk 1.6.0_15-b03,eclipse 3.5 SR1.

Package test; public class Test {public static void main (string[] args) {int loop = 10000000;//Test 10 million loop String num = "0";//----First time-- --{System.out.print ("first time:/T"); Long start = System.currenttimemillis (); for (int i = 0; I < loop; i++) {Class1 C1 = New Class1 (); C1.SETF1 (num); C1.GETF1 (); } System.out.printf ("%5dms", (System.currenttimemillis ()-start); Start = System.currenttimemillis (); for (int i = 0; I < loop; i++) {Class2 C2 = new Class2 (); C2.SETF1 (num); C2.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); Start = System.currenttimemillis (); Class1 C1 = new Class1 (); for (int i = 0; I < loop; i++) {C1.SETF1 (num); C1.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); Start = System.currenttimemillis (); Class2 C2 = new Class2 (); for (int i = 0; I < loop; i++) {C2.SETF1 (num); C2.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); }//----second----{System.out.print ("N/a second:/T"); long sTart = System.currenttimemillis (); for (int i = 0; I < loop; i++) {Class1 C1 = new Class1 (); C1.SETF1 (num); C1.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); Start = System.currenttimemillis (); for (int i = 0; I < loop; i++) {Class2 C2 = new Class2 (); C2.SETF1 (num); C2.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); Start = System.currenttimemillis (); Class1 C1 = new Class1 (); for (int i = 0; I < loop; i++) {C1.SETF1 (num); C1.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); Start = System.currenttimemillis (); Class2 C2 = new Class2 (); for (int i = 0; I < loop; i++) {C2.SETF1 (num); C2.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); }//----third----{System.out.print ("N/T Third:/T"); Long start = System.currenttimemillis (); for (int i = 0; I < loop; i++) {Class1 C1 = new Class1 (); C1.SETF1 (num); C1.GETF1 ();} System.out.printf ("%5dms", System.currenttimemilLis ()-start); Start = System.currenttimemillis (); for (int i = 0; I < loop; i++) {Class2 C2 = new Class2 (); C2.SETF1 (num); C2.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); Start = System.currenttimemillis (); Class1 C1 = new Class1 (); for (int i = 0; I < loop; i++) {C1.SETF1 (num); C1.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); Start = System.currenttimemillis (); Class2 C2 = new Class2 (); for (int i = 0; I < loop; i++) {C2.SETF1 (num); C2.GETF1 ();} System.out.printf ("%5dms", (System.currenttimemillis ()-start); }} class Class1 {private string F1 public string getF1 () {return f1;} public void SetF1 (String f1) {this.f1 = F1; Final class Class2 {private string F1; public final String getF1 () {return F1;} public final void setF1 (String F1) {this.f1 = F1;} }

Run Result:

First time: 110ms 1203ms 16ms 156ms Second: 94ms 1203ms 15ms 141ms Third: 94ms 1203ms 15ms 141ms

Summarize:

1. The use of final inline optimization is ineffective;

2. Sometimes the results are often unexpected.