puzzled with java if else performance
- by user1906966
I am doing an investigation on a method's performance and finally identified the overhead was caused by the "else" portion of the if else statement. I have written a small program to illustrate the performance difference even when the else portion of the code never gets executed:
public class TestIfPerf
{
public static void main( String[] args )
{
boolean condition = true;
long time = 0L;
int value = 0;
// warm up test
for( int count=0; count<10000000; count++ )
{
if ( condition )
{
value = 1 + 2;
}
else
{
value = 1 + 3;
}
}
// benchmark if condition only
time = System.nanoTime();
for( int count=0; count<10000000; count++ )
{
if ( condition )
{
value = 1 + 2;
}
}
time = System.nanoTime() - time;
System.out.println( "1) performance " + time );
time = System.nanoTime();
// benchmark if else condition
for( int count=0; count<10000000; count++ )
{
if ( condition )
{
value = 1 + 2;
}
else
{
value = 1 + 3;
}
}
time = System.nanoTime() - time;
System.out.println( "2) performance " + time );
}
}
and run the test program with java -classpath . -Dmx=800m -Dms=800m TestIfPerf.
I performed this on both Mac and Linux Java with 1.6 latest build. Consistently the first benchmark, without the else is much faster than the second benchmark with the else section even though the code is structured such that the else portion is never executed because of the condition. I understand that to some, the difference might not be significant but the relative performance difference is large. I wonder if anyone has any insight to this (or maybe there is something I did incorrectly).
Linux benchmark (in nano)
performance 1215488
performance 2629531
Mac benchmark (in nano)
performance 1667000
performance 4208000
