Inheritance - Data Structures and Problem Solving Using Java - page 149

1 import java.math.BigInteger;
2
3 class FindMaxDemo
4 {
5 /**
6 * Return max item in a.
7 * Precondition: a.length > 0
8 */
9 public static Comparable findMax( Comparable [ ] a )
10 {
11 int maxIndex = 0;
12
13 for( int i = 1; i < a.length; i++ )
14 if( a[ i ].compareTo( a[ maxIndex ] ) > 0 )
15 maxIndex = i;
16
17 return a[ maxIndex ];
18 }
19
20 /**
21 * Test findMax on BigInteger and String objects.
22 */
23 public static void main( String [ ] args )
24 {
25 BigInteger [ ] bi1 = { new BigInteger( "8764" ),
26 new BigInteger( "29345" ),
27 new BigInteger( "1818" ) };
28
29 String [ ] st1 = { "Joe", "Bob", "Bill", "Zeke" };
30
31 System.out.println( findMax( bi1 ) );
32 System.out.println( findMax( st1 ) );
33 }
34 }

figure 4.29
A generic findMax
routine, with demo
using shapes and
strings (pre-Java 5)

Fourth, it is not required that the interface be a standard library interface.
Finally, this solution does not always work, because it might be impossi-
ble to declare that a class implements a needed interface. For instance, the
class might be a library class, while the interface is a user-defined interface.
And if the class is final, we can't even create a new class. Section 4.8 offers
another solution for this problem, which is the function object . The function
object uses interfaces also, and is perhaps one of the central themes encoun-
tered in the Java library.