Public interface Relation {

// returns true if a > b

public boolean isGreater( Object a, Object b );

//returns true if a < b

public boolean isLess( Object a, Object b );

//returns true if a == b

public boolean isEqual( Object a, Object b );

}

Public class Line implements Relation {

// variables

private double x1;  //x- value

private double x2;  //x- value

private double y1;  //y- value

private double y2;  //y- value

// Constructor

public Line ( double x1, double y1, double x2, double, y2) {

          this.x1 = x1;

          this.x2 = x2;

          this.y1 = y1;

          this.y2 = y2;

}

// Calculate length

public double length( ) {

     return Math.sqrt( (x2-x1) * ( x2-x1) + (y2-y1) * (y2-y1) );

}

// returns true if a > b

public boolean isGreater( Object a, Object b );

     return ((Line)a).length() > ((Line)b).length();

}

//returns true if a < b

public boolean isLess( Object a, Object b );

     return ((Line)a).length() < ((Line)b).length();

}

//returns true if a == b

public boolean isEqual( Object a, Object b );

     return ((Line)a).length() == ((Line)b).length();

}

// toString

public String toString ( ) {

     String s;

     s = “Line from (“ + x1 + “,” + y1 + “) to (“

         + x2 + “,” + y2 + “): Length = “ + length();

     return s;

}

}

public class TestLine {

// main

public static void main(String[] args) {

// Create Objects

o[0] = new Line(0,0,2,1);

o[1] = new Line(0,0,1,-1);

o[2] = new Line(-1,1,1,1);

o[3] = new Line(2,0,0,0);

o[4] = new Line(0,2,-2,0);

// Sorte objects

SortObj.sort(o);

//Show results

for ( int i = 0; i < o.length; i++) {

     System.out.println(o[i].toString());

}

}

}

// Define sort method

public class SortObj {

// Declare variables

     int i,j;  //indices

     int iptr;  // pointer to smallest

     Object temp;   //temp variable for swapping

//Sort values

for ( i = 0; i < o.length; i++ ) {

   //Find minimum value

      iptr = i;

      for ( j = i + 1; j < o.length; j++

        if ( ( (Relation)o[0]).isLess(

           (Relation) o[j], (Relation) o[iptr] ))

              iptr = j;

        }

// iptr now points to the min value, so swap

     if ( i != iptr ) {

        temp = o[i];

        o[i] = o[iptr];

        o[iptr] = temp;

        }

     }

//Return sorted objects

return o;

}

}