Programming and Problem Solving with Java

CASE STUDY

406

fields. So, we must make the event handler be an instance class (not static). What does

the event handler do when the user clicks the button? It gets the string from the input

field, converts it to a doublevalue (using parseDouble), adds it to the total, updates the

output label, and resets the input field to 0.0.

We are now ready to code the Stationclass.

//****************************************************************************

// This package provides a class for rainfall reporting stations. Each

// station is represented by a separate panel that contains its own

// user interface elements.

//****************************************************************************

package station;

importjava.awt.*; // Layout manager

importjava.awt.event.*; // Event-handling classes

importjavax.swing.*; // User interface classes

public class Station

{

JButton enter; // Enter data button

JTextField amountField; // Data entry field

JLabel outputLabel; // Result display label

JPanel panel; // Panel for user interface

ActionHandler action; // Event handler

doubletotal = 0.0; // Total rainfall

publicStation (String name) // Station constructor

{

// Set up panel to hold user interface elements

panel = newJPanel(); // Get a panel

panel.setLayout(newFlowLayout()); // Set layout for the panel

// Create user interface elements

amountField = newJTextField("0.0", 10 ); // Field for data entry

enter = newJButton("Enter"); // Enter button

action = newActionHandler(); // Create an event handler

enter.addActionListener(action); // Register handler with button

outputLabel = newJLabel("Total Rainfall: " // Label for output

+ total);

// Add user interface elements to panel

panel.add(newJLabel("Station "+ name + ":"));

Private Class ActionHandler implements ActionListener

Public void method actionPerformed takes one parameter, event, of class ActionEvent

Declare a local variable, value, of type double, to hold the input value

Assign value the result of applying parseDouble to the value from

amountField.getText

Set total to total plus value

Use setText to update outputLabel with "Total Rainfall: " + total

Use setText to reset amountField to "0.0"