Sorting custom objects with Java collections

[M Burke]

Lets say I have a custom data object...

class Data{
String firm;
String date;
int grossSales;
int netSales;
}

And I want to drop a bunch of these data objects into a Java Collection (Vector? ArrayList? not sure).
How can I sort it on the avalable fields, first by firm, then date?

Thanks

[Dmitry Melnik]

How about this?

java.util.Collections.sort(yourList,aComparator);
[ August 03, 2004: Message edited by: Dmitry Melnik ]

[Ben Ethridge]

I just used the Comparator the way Dmitry described. It's not simple to understand at first, i.e. takes some reading and study (in the javadocs and looking at some simple examples), but it's very powerful once you get the hang of it.

A google search on "Comparator" will probably find you what you need.

Ben

[William Brogden]

Like Ben said, Comparators are powerful whenyou get the hang of it. Here is something I just wrote to create Comparators for sorting ArrayLists of File objects.

  // s is either "lastmod" or "size"
  Comparator getFileDataComparator( String s ){
    if( s.equals("lastmod") ){
      return new Comparator(){
         public int compare( Object a, Object b ){
           FileData fdA = (FileData) a ;
           FileData fdB = (FileData) b ;
           if( fdA.lastmod == fdB.lastmod ) return 0;
           if( fdA.lastmod < fdB.lastmod ) return -1 ;
           return 1 ; // by elimination
         }
         public boolean equals( Object c ){ return false ; }
      };
    }
    if( s.equals("size") ){
      return new Comparator(){
         public int compare( Object a, Object b ){
           FileData fdA = (FileData) a ;
           FileData fdB = (FileData) b ;
           if( fdA.size == fdB.size ) return 0;
           if( fdA.size < fdB.size ) return -1 ;
           return 1 ; // by elimination
         }
         public boolean equals( Object c ){ return false ; }
      };
    }
    return null;
  }
  

Bill

[M Burke]

Thanks, I will take a look at it.