Searching and Sorting - A Concise and Practical Introduction to Programming Algorithms in Java - page 137

{year=y; month=m; day=d;}

static void Display(EventObject obj)
{System.out.println(obj.year+"/"+obj.month+"/"+obj.day);}
}

Then the two primitives are redefined as follows:

Program 6.7 Redefining the predicate/swap primitives for sorting other
types of elements
static boolean GreaterThan(EventObject a , EventObject b)
{ return (( a . year > b.year) ||
( (a. year==b. year) && (a.month > b.month)) ||
((a.year==b.year) && (a.month==b.month) && (a.day > b.day)) )
; }

static void swap (EventObject [ ] array , int i, int j)

{ EventObject tmp=array [ i ] ;
array [ i]=array [ j ];
array [ j]=tmp;
}

Observe once again that for non-primitive types, we design a tailor >= predicate
since the usual predicate will only compare references on these objects. Let us
put the pieces altogether and demonstrate selection sorting on a set of events:

Program 6.8 Selection sort on a set of EventObject elements
static void SelectionSort(EventObject [] array)
int n=array . length ;

for ( int i=0;i < n − 1; i ++)
for ( int j=i +1;j < n ; j ++)
if (GreaterThan(array [ i ] , array [ j ]) )
swap(array , i , j ) ;

}

public static void main( String [ ] args )

{ EventObject

[ ] array= new EventObject[5];

array [0]= new EventObject(2008 ,06 ,01) ;
array [1]= new EventObject(2005 ,04 ,03) ;
array [2]= new EventObject(2005 ,05 ,27) ;
array [3]= new EventObject(2005 ,04 ,01) ;
array [4]= new EventObject(2005 ,04 ,15) ;

SelectionSort(array) ;
for ( int i=0;i < array . length ; i++)
EventObject.Display(array[i]);
System . out . println ( "" );