Defining Classes II - Absolute Java - page 283

PITFALL: A Wrapper Class Does Not Have a
No-Argument Constructor

Normally, it is good programming practice to define a no-argument constructor for
any class you define. However, on rare occasions, a no-argument constructor simply
does not make sense. The wrapper classes discussed in the previous subsection do not
have a no-argument constructor, which is reasonable if you think about it. To use
the static methods in a wrapper class, you need no calling object and hence need no
constructor at all. The other function of a wrapper class is to provide a class object
corresponding to a value of a primitive type. For example,

new Integer(42)

creates an object of the class Integer that corresponds to the int value 42 . There is
no no-argument constructor for the class Integer , because it makes no sense to have
an object of the class Integer unless it corresponds to an int value, and if it does cor-
respond to an int value, that int value is naturally an argument to the constructor.

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Display 5.9 String Processing with a Method from the Class Character (part 1 of 2)

1 import java.util.Scanner;

2 /**
3 Illustrate the use of a static method from the class Character.
4 */
5
6 public class StringProcessor
7 {
8 public static void main (String[] args)
9 {
10 System.out.println("Enter a one line sentence:");
11 Scanner keyboard = new Scanner(System.in);
12 String sentence = keyboard.nextLine();
13
14 sentence = sentence.toLowerCase();
15 char firstCharacter = sentence.charAt(0);
16 sentence = Character.toUpperCase(firstCharacter)
17 + sentence.substring(1);
18
19 System.out.println("The revised sentence is:");
20 System.out.println(sentence);
21 }
22 }

(continued)