Sorting and Searching - Java Concepts - page 896

C OMMON E RROR 14.1: The compareTo Method Can
Return Any Integer, Not
JustÉČÉ1, 0, and 1
The call a.compareTo(b) is allowed to return any negative integer to
denote that a should come before b , not necessarily the valueɨ1. That is, the test
if (a.compareTo(b) == -1) // ERROR!
is generally wrong. Instead, you should test
if (a.compareTo(b) < 0) // OK
Why would a compareTo method ever want to return a number other thanɨ1, 0,
or 1 ? Sometimes, it is convenient to just return the difference of two integers. For
example, the compareTo method of the Stri ng class compares characters
in matching positions:
char c1 = charAt(i);
char c2 = other.charAt(i);
If the characters are different, then the method simply returns their difference:
if (c1 ! = c2) return c1 - c2;
This difference is a negative number if c1 is less than c2 , but it is not necessarily
the numberɨ1.
A DVANCED T OPIC 14.4: The Parameterized
Comparable Interface
As of Java version 5.0, the Comparabl e interface is a parameterized type,
similar to the Array-List type:
public interface Comparable <T>
{
int compareTo( T other)
}