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From David kerber <dcker...@verizon.net>
Subject Re: Performance: switch vs if ... else if
Date Tue, 19 May 2009 19:51:20 GMT
Caldarale, Charles R wrote:
>> From: David kerber [mailto:dckerber@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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