ELEMENTARY PROGRAMMING - Introduction to Java Programming - page 70

2.19 Getting Input from Input Dialogs
An input dialog box prompts the user to enter an input graphically.

Key
Point

You can obtain input from the console. Alternatively, you can obtain input from an input dia-
log box by invoking the JOptionPane.showInputDialog method, as shown in Figure 2.4. JOptionPane class

String input =
JOptionPane.showInputDialog(
"Enter an input" );

Click OK to accept
input and close
the dialog

Click Cancel to close the
dialog without input

F IGURE 2.4

The input dialog box enables the user to enter a string.

When this method is executed, a dialog is displayed to enable you to enter an input value.
After entering a string, click OK to accept the input and close the dialog box. The input is
returned from the method as a string.
There are several ways to use the showInputDialog method. For the time being, you
need to know only two ways to invoke it.
One is to use a statement like this one:

showInputDialog method

JOptionPane.showInputDialog(x);

where x is a string for the prompting message.
The other is to use a statement such as the following:

String string = JOptionPane.showInputDialog( null , x,
y, JOptionPane.QUESTION_MESSAGE);

where x is a string for the prompting message and y is a string for the title of the input dialog
box, as shown in the example below.

String input =
JOptionPane.showInputDialog( null ,
"Enter an input" ,
"Input Dialog Demo" ,
JOptionPane.QUESTION_MESSAGE);

2.19.1 Converting Strings to Numbers
The input returned from the input dialog box is a string. If you enter a numeric value such as 123 ,
it returns "123" . You have to convert a string into a number to obtain the input as a number.
To convert a string into an int value, use the Integer.parseInt method, as follows:

Integer.parseInt method

int intValue = Integer.parseInt(intString);

where intString is a numeric string such as 123 .
To convert a string into a double value, use the Double.parseDouble method, as follows:

Double.parseDouble
method

double doubleValue = Double.parseDouble(doubleString);

where doubleString is a numeric string such as 123.45 .
The Integer and Double classes are both included in the java.lang package, and thus
they are automatically imported.