ABSTRACT CLASSES AND INTERFACES - Introduction to Java Programming: Comprehensive Version - page 510

Thus, numbers are comparable, strings are comparable, and so are dates. You can use the
compareTo method to compare two numbers, two strings, and two dates. For example, the
following code

1 System.out.println( new Integer( 3 ).compareTo( new Integer( 5 )));
2 System.out.println( "ABC" .compareTo( "ABE" ));
3 java.util.Date date1 = new java.util.Date( 2013 , 1 , 1 );
4 java.util.Date date2 = new java.util.Date( 2012 , 1 , 1 );
5 System.out.println(date1.compareTo(date2));

displays

-1
-2
1

Line 1 displays a negative value since 3 is less than 5 . Line 2 displays a negative value
since ABC is less than ABE . Line 5 displays a positive value since date1 is greater than
date2 .
Let n be an Integer object, s be a String object, and d be a Date object. All the follow-
ing expressions are true .

n instanceof Integer s instanceof String d instanceof java.util.Date

n instanceof Object s instanceof Object d instanceof Object

n instanceof Comparable s instanceof Comparable d instanceof Comparable

Since all Comparable objects have the compareTo method, the java.util.Arrays
.sort(Object[]) method in the Java API uses the compareTo method to compare and
sorts the objects in an array, provided that the objects are instances of the Comparable inter-
face. Listing 13.8 gives an example of sorting an array of strings and an array of BigInteger
objects.

L ISTING 13.8

SortComparableObjects.java
1 import java.math.*;
2
3 public class SortComparableObjects {
4 public static void main(String[] args) {
5 String[] cities = { "Savannah" , "Boston" , "Atlanta" , "Tampa" };
6 java.util.Arrays.sort(cities);
7 for (String city: cities)
8 System.out.print(city + " " );
9 System.out.println();
10
11 BigInteger[] hugeNumbers = { new BigInteger( "2323231092923992" ),
12 new BigInteger( "432232323239292" ),
13 new BigInteger( "54623239292" )};
14 java.util.Arrays.sort(hugeNumbers);
15 for (BigInteger number: hugeNumbers)
16 System.out.print(number + " " );
17 }
18 }

create an array
sort the array

create an array

sort the array