DO NOT REPLY [Bug 22973] New: - [collections] [PATCH] patch to reduce object creation in CollectionUtils

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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=22973

[collections] [PATCH] patch to reduce object creation in CollectionUtils

           Summary: [collections] [PATCH] patch to reduce object creation in
                    CollectionUtils
           Product: Commons
           Version: Nightly Builds
          Platform: Other
        OS/Version: Other
            Status: NEW
          Severity: Minor
          Priority: Other
         Component: Collections
        AssignedTo: [EMAIL PROTECTED]
        ReportedBy: [EMAIL PROTECTED]


The attached patch reduces the number of Integer objects created when invoking
CollectionUtils.getCardinalityMap(final Collection col). The number of Integers
created is reduced by the count of unique objects within col.

The patch does not change the basic algorithm so the simplicity of the method is
not lost.

The change was profiled with the class below. These are the absolute times for
JDK 1.3.1_04 and 1.4.1_03

       1.4         1.3
pre:   168267      153849
post:  164473      150866

and normalised to the pre version for each JDK

       1.4         1.3
pre:   1.00        1.00
post:  0.98        0.98

so there was only a minor speed difference however the reduction in the number
of created objects has a memory use advantage. It was surprising to see that JDK
1.4.1 was slower than 1.3.1, in this limited test. The binaries were compiled
with JDK 1.4.1.

This is the test class:

import org.apache.commons.collections.CollectionUtils ;

import java.util.*;

public class CollectionUtilsTest {


    Set a ;
    Set b ;
    Set c ;

    Collection cols []  ;

    long startMillis ;
    void init () {

        a = new HashSet () ;
        for ( int i = 1 ; i <= 10000 ; i++ ) {
            a.add ( new Integer ( i ) ) ;
        }

        b = new HashSet () ;
        for ( int i = 5001 ; i <= 15000 ; i++ ) {
            b.add ( new Integer ( i ) ) ;
        }

        c = new HashSet () ;
        for ( int i = 1001 ; i <= 20000 ; i++ ) {
            c.add ( new Integer ( i ) ) ;
        }

        cols = new Collection [] { a, b, c } ;

        startMillis = System.currentTimeMillis () ;
    }


    void run () {

        for ( int i = 0 ; i < 3 ; i++ ) {
            for ( int j = 0 ; j < 3 ; j++ ) {
                CollectionUtils.union ( cols [ i ], cols [ j ] ) ;
                CollectionUtils.intersection ( cols [ i ], cols [ j ] ) ;
                CollectionUtils.disjunction ( cols [ i ], cols [ j ] ) ;
                CollectionUtils.subtract ( cols [ i ], cols [ j ] ) ;
            }
        }

    }


    void report () {

        System.out.println ( "Elapsed millis: " + ( System.currentTimeMillis () -
startMillis ) ) ;
    }



    public static void main ( String  [] arg ) {

        CollectionUtilsTest t = new CollectionUtilsTest () ;

        t.init () ;
        t.run () ;
        t.report () ;

    }
}

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