sort1 - B asic T e r m s 3.1 E le m e n t a r y S o r t s...

Robert Sedgewick and Kevin Wayne • Copyright © 2005 • http://www.Princeton.EDU/~cos226
3.1 Elementary Sorts
Reference: Chapter 6, Algorithms in Java, 3 rd Edition, Robert Sedgewick.
2
Basic Terms
Ex: student record in a University.
Sort: rearrange sequence of objects into ascending order.
3
Rules of the Game
Goal. Write robust sorting library that can sort any type of data
into sorted order using the data type's natural order.
Callbacks.
!
Client passes array of objects to sorting routine.
!
Sorting routine calls back object's comparison function as needed.
Implementing callbacks.
!
Java: interfaces .
!
C: function pointers.
!
C++: functors.
!
C#: delegates.
!
Lisp: first class functions.
client
data type
sorting library
construct
callbacks
compare
sort
4
Comparable Interface
Comparable interface. Require a method so that
v.compareTo(w)
returns:
!
A negative integer if v is less than w .
!
A positive integer if
v
is greater than
w
.
!
Zero if
v
is equal to
w
.
Consistency. It is the programmer's responsibility to ensure that
compareTo()
specifies a total order.
!
Transitivity: if a < b and b < c, then a < c.
!
Trichotomy: either (i) a < b or (ii) b < a or (iii) a = b.
Built-in comparable types.
String
,
Double
,
Integer
,
Date
,
File
.
User-defined comparable types. Implement the
Comparable
interface.

5
Implementing the Comparable Interface: Date
public class Date implements Comparable < Date > {
private int month , day , year ;
public