programming
Graphical GUI user interfacebased programming
Windchill
Windchill There are several formulas for calculating the windchill temperature twc The one provided by U.S. National Weather Service and is applicable for a windspeed greater than four miles per hour
twc = 0.081(t - 91.4)(3.71 v + 5.81 - 0.25v) + 91.4
Where Variable t is the Fahrenheit temperature Variable v is the windspeed in miles per hour
Consolebased programming
Console program
Method main() { statement1; statement2; ... statementm; }
Console program s begin and end in m et hod m ain( )
In use
Pr ogr am needs to r espond whenev er the r un button is click ed
Ther e needs to be an ev ent loop that is look ing for user inteface ev ents
GUIbased programming
GUI program begins in m et hod m ain( ) . The m et hod creat es a new inst ance of t he GUI by invoking t he GUI const ruct or. On com plet ion, t he event dispat ching loop is begun
GUI Program
main() { GUI gui = new GUI(); } GUI Constructor() { constructor1; constructor2; ... constructorn; } Action Performer() { action1; action2; ... actionk; }
Const ruct or configures t he com ponent s of t he GUI . I t also regist ers t he list ener perform er for user int eract ions
Event-dispatching loop
do if an event occurs then signal its action listeners until program ends
The event dispat ching loop wat ches for user int eract ions wit h t he GUI . When an event occurs, it s list ener perform ers are not ified The act ion perform er im plem ent s t he t ask of t he GUI . Aft er it com plet es, t he event dispat ching loop is rest art ed
Java support
JFrame Represents a titled, bordered window JLabel Represents a display area suitable for one or both of a singleline text or image. JTextField Represents an editable singleline text entry component JButton Represents a push button JTextArea Represents an editable multiline text entry component
Instance variables
private JFrame window References the window containing the other components of the GUI
Instance variables
private JTextArea legendArea References the text display for the multiline program legend
Instance variables
private JLabel fahrTag References the label for the data entry area supplying the temperature
Instance variables
private JTextField fahrText References the data area supplying the temperature
Instance variables
private JLabel windTag References the label for the data entry area supplying the windspeed
Instance variables
private JTextField windText References the data area supplying the windspeed
Instance variables
private JLabel chillTag References the label for the data area giving the windchill
Instance variables
private JTextField chillText References the data area giving the windchill
Class constants
private static final String LEGEND = "This windchill calculator" + "is intended for velocities greater than 4 mph." Program legend text
Class constants
private static final int WINDOW_WIDTH = 350 Initial width of the GUI
Class constants
private static final int WINDOW_HEIGHT = 185 Initial height of the GUI
Class constants
private static final int AREA_WIDTH = 40 Width of the program legend in characters
Class constants
private static final int FIELD_WIDTH = 40 Number of characters per data entry area
Class constants
private static final FlowLayout LAYOUT_STYLE = new FlowLaout() References manager that lays out GUI components in a topto bottom, lefttoright manner
Class constants
private static FlowLayout LAYOUT_STYLE = new FlowLaout() References manager that lays out GUI components in a topto bottom, lefttoright manner
Class constants
private static FlowLayout LAYOUT_STYLE = new FlowLaout() References manager that lays out GUI components in a topto bottom, lefttoright manner
Program Windchill.java
import javax.swing.*; import java.awt.*; import java.awt.event.*; public class Windchill implements ActionListener { // class constants // instance variables with initialization // Windchill(): default constructor // actionPerformed(): run button action event handler // main(): application entry point }
Program Windchill.java class constants
private static final int WINDOW_WIDTH = 350; // pixels private static final int WINDOW_HEIGHT = 185; // pixels private static final int FIELD_WIDTH = 20; // characters private static final int AREA_WIDTH = 40; // characters private static final FlowLayout LAYOUT_STYLE = new FlowLayout(); private static final String LEGEND = "This windchill " + "calculator is intended for velocities greater than 4 mph.";
Program Windchill.java instance variables
// window for GUI private JFrame window = new JFrame("Windchill Calculator"); // legend private JTextArea legendArea = new JTextArea(LEGEND, 2, AREA_WIDTH); // user entry area for temperature private JLabel fahrTag = new JLabel("Fahrenheit temperature"); private JTextField fahrText = new JTextField(FIELD_WIDTH);
Program Windchill.java instance variables
// user entry area for windspeed private JLabel windTag = new JLabel(" Windspeed (mph)"); private JTextField windText = new JTextField(FIELD_WIDTH); // entry area for windchill result private JLabel chillTag = new JLabel(" Windchill temperature"); private JTextField chillText = new JTextField(FIELD_WIDTH); // run button private JButton runButton = new JButton("Run");
Program Windchill.java constructor
public Windchill() { // configure GUI // register event listener // add components to container // display GUI }
Program Windchill.java constructor
public { Windchill() // configure GUI window.setSize(WINDOW_WIDTH, WINDOW_HEIGHT); window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); legendArea.setEditable(false); legendArea.setLineWrap(true); legendArea.setWrapStyleWord(true); legendArea.setBackground(window.getBackground()); chillText.setEditable(false); chillText.setBackground(Color.WHITE);
Bad line wrapping
It is important to make program legends uneditable
Program Windchill.java constructor
public Windchill() { // configure GUI window.setSize(WINDOW_WIDTH, WINDOW_HEIGHT); window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); legendArea.setEditable(false); legendArea.setLineWrap(true); legendArea.setWrapStyleWord(true); legendArea.setBackground(window.getBackground()); chillText.setEditable(false); chillText.setBackground(Color.WHITE);
Dangers of an editable legend
Line wrapping in the middle of a word
Program Windchill.java constructor
public Windchill() { // configure GUI window.setSize(WINDOW_WIDTH, WINDOW_HEIGHT); window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); legendArea.setEditable(false); legendArea.setLineWrap(true); legendArea.setWrapStyleWord(true); legendArea.setBackground(window.getBackground()); chillText.setEditable(false); chillText.setBackground(Color.WHITE);
Bad line wrapping
A JLabel is noneditable by the user
By default the text field of a JTextField is editable by the user
Program Windchill.java constructor
public Windchill() { // configure GUI ... // register event listener runButton.addActionListener(this);
Run button actionevent handling
Act ion event s are sent t o regist ered act ion list eners An Act ionList ener has an act ionPerform er( ) m et hod t hat handles t he class specific act ivit y GUI : Action Listener actionPerformer() Method
Action Event
Get data entries from temperature and windspeed data areas Compute windchill according to the Weather Service formula Display result to windchill data area
When t he run but t on is clicked, it dispat ches an act ion event
Program Windchill.java constructor
public Windchill() { // configure GUI ... // register event listener ... // add components to container Container c = window.getContentPane(); c.setLayout(LAYOUT_STYLE); c.add(legendArea); c.add(fahrTag); c.add(fahrText); c.add(windTag); c.add(windText); c.add(chillTag); c.add(chillText); c.add(runButton);
Program Windchill.java constructor
public Windchill() { // configure GUI ... // register event listener ... // add components to container ... // make GUI visible window.setVisible(true);
Laying out the GUI components
Top to bottom, left to right
Program Windchill.java action performer
public void actionPerformed(ActionEvent e) { // get user's responses // compute windchill } // display windchill
Program Windchill.java action performer
public void actionPerformed(ActionEvent e) { // get user's responses String response1 = fahrText.getText(); double t = Double.parseDouble(response1); String response2 = windText.getText(); double v = Double.parseDouble(response2); // compute windchill } // display windchill
Program Windchill.java action performer
Program Windchill.java action performer
public void actionPerformed(ActionEvent e) { // get user's responses String response1 = fahrText.getText(); double t = Double.parseDouble(response1); String response2 = windText.getText(); double v = Double.parseDouble(response2); // compute windchill double windchillTemperature = 0.081 * (t 91.4) ...