INTRODUCTION TO OBJECTS AND INPUT/OUTPUT - Java Programming: From Problem Analysis to Program Design - page 139

Note that Integer , Float ,and Double are classes that contain methods to convert a
numeric string into a number. These classes are called wrapper classes. Moreover,
parseInt is a method of the class Integer , which converts a numeric integer
string into a value of the type int . Similarly, parseFloat is a method of the class
Float andisusedtoconvertanumericdecimalstringintoanequivalentvalueof
the type float , and the method parseDouble is a method of the class Double ,
which is used to convert a numeric decimal string into an equivalent value of the
type double . At this point, do not be overly concerned with the details of these
classes and methods; just continue to use them as shown previously whenever you
need them. (Chapter 6 discusses these wrapper classes in more detail.)

3

EXAMPLE 3-8

1.

Integer.parseInt("34") ¼ 34

Integer.parseInt("-456") ¼ -456

Double.parseDouble("754.89") ¼ 754.89

2.

¼ 34 + 75 ¼ 109

Integer.parseInt("34") + Integer.parseInt("75")

Integer.parseInt("87") + Integer.parseInt("-67") ¼ 87 - 67 ¼ 20

3.

Double.parseDouble("754.89") - Double.parseDouble("87.34")

¼ 754.89 - 87.34

¼ 667.55

Using Dialog Boxes for Input/Output
Recall that you have already used the class Scanner to input data into a program from
the keyboard, and you used the object System.out to output the results to the screen.
Another way to gather input and output results is to use a graphical user interface (GUI).
Java provides the class JOptionPane , which allows the programmer to use GUI
components for I/O. This section describes how to use these facilities to make I/O
more efficient and the program more attractive.
The class JOptionPane is contained in the package javax.swing .Thetwo
methods of this class that we use are: showInputDialog and showMessageDialog .
The method showInputDialog allows the user to input a string from the keyboard;
the method showMessageDialog allows the programmer to display the results.
The syntax to use the method showInputDialog is:

str = JOptionPane.showInputDialog(stringExpression);