If you're only doing a single character, you would probably get better
performance with:
switch (sString.char(0)) {
case 'A':
case 'B':
case 'C':
}
David kerber wrote:
Caldarale, Charles R wrote:
From: David kerber [mailto:dcker...@verizon.net]
Subject: Performance: switch vs if ... else if
I had to process based on a parameter that could take
one of 6 different single-character string values. I
had been using an if .. else if construct.
Interesting numbers. Can you show us the exact code of the if ..
else construct?
- Chuck
Here is the entire code. The variables o and p are used to make sure
there is actually some work done in each call to the test methods.
I've seen cases (mainly in Delphi) where an optimizer completely
removed large chunks of code because it wasn't doing anything. I
don't know of java can do that or not...
public class SwitchVsIfTest {
static enum rtFields{ c, r, l, a, t, d }
static long n = 100000000;
static long o = 0;
static long p = 0;
public static void main( String[] args ) {
long t1;
long t2;
long t3;
long t4;
t1 = System.currentTimeMillis();
for ( int ii = 0; ii < n; ii++ ) {
switchSub( "c" );
switchSub( "r" );
switchSub( "l" );
switchSub( "a" );
switchSub( "t" );
switchSub( "d" );
}
t2 = System.currentTimeMillis();
System.out.println( "Elapsed time for 'switch' version: " + (
t2 - t1 ) + ", counter = " + o );
t3 = System.currentTimeMillis();
for ( int jj = 0; jj < n; jj++ ) {
ifSub( "c" );
ifSub( "r" );
ifSub( "l" );
ifSub( "a" );
ifSub( "t" );
ifSub( "d" );
}
t4 = System.currentTimeMillis();
System.out.println( "Elapsed time for 'if' version: " + ( t4 -
t3 ) + ", counter = " + p );
t1 = System.currentTimeMillis();
for ( int ii = 0; ii < n; ii++ ) {
switchSub( "c" );
switchSub( "r" );
switchSub( "l" );
switchSub( "a" );
switchSub( "t" );
switchSub( "d" );
}
t2 = System.currentTimeMillis();
System.out.println( "Elapsed time for 'switch' version: " + (
t2 - t1 ) + ", counter = " + o );
t3 = System.currentTimeMillis();
for ( int jj = 0; jj < n; jj++ ) {
ifSub( "c" );
ifSub( "r" );
ifSub( "l" );
ifSub( "a" );
ifSub( "t" );
ifSub( "d" );
}
t4 = System.currentTimeMillis();
System.out.println( "Elapsed time for 'if' version: " + ( t4 -
t3 ) + ", counter = " + p );
}
private static void switchSub( String myChr ) {
switch ( rtFields.valueOf( myChr )) {
case c:
o += 1;
break;
case r:
o += 2;
break;
case l:
o += 3;
break;
case a:
o += 4;
break;
case t:
o += 5;
break;
case d:
o += 6;
break;
}
return;
}
private static void ifSub( String myChr ) {
if ( myChr.equals( "c" )) {
p += 1;
} else if (myChr.equals( "r" )) {
p += 2;
} else if (myChr.equals( "l" )) {
p += 3;
} else if (myChr.equals( "a" )) {
p += 4;
} else if (myChr.equals( "t" )) {
p += 5;
} else if (myChr.equals( "d" )) {
p += 6;
}
}
}
D
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