Question

GUI Programming

Run and review kiloconverter.java. Then answer the following questions:

. What is the window title?

. What type of object is calcButton?

. What is the name of the JPanel variable in buildPanel?

. What three components get added to the panel?

. How does the program show its results: a message dialog, or on the console?

. What variable is kiloTextField.getText() assigned to?

. What method is used to convert the input string to a Double?

. What method gets called to display the window? (What method makes the window visible?)

. What class does KiloConverter extend?

. What interface does calcButtonListener implement?

// Code courtesy of Gaddis, Getting Started with Java, 6th Edition
import javax.swing.*; // Needed for Swing classes
import java.awt.event.*; // Needed for ActionListener Interface

/**
The KiloConverter class displays a JFrame that
lets the user enter a distance in kilometers. When
the Calculate button is clicked, a dialog box is
displayed with the distance converted to miles.
*/

public class KiloConverter extends JFrame
{
private JPanel panel; // To reference a panel
private JLabel messageLabel; // To reference a label
private JTextField kiloTextField; // To reference a text field
private JButton calcButton; // To reference a button
private final int WINDOW_WIDTH = 310; // Window width
private final int WINDOW_HEIGHT = 100; // Window height

/**
Constructor
*/

public KiloConverter()
{
// Set the window title.
setTitle("Kilometer Converter");

// Set the size of the window.
setSize(WINDOW_WIDTH, WINDOW_HEIGHT);

// Specify what happens when the close button is clicked.
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

// Build the panel and add it to the frame.
buildPanel();

// Add the panel to the frame's content pane.
add(panel);

// Display the window.
setVisible(true);
}

/**
The buildPanel method adds a label, text field, and
and a button to a panel.
*/

private void buildPanel()
{
// Create a label to display instructions.
messageLabel = new JLabel("Enter a distance " +
"in kilometers");

// Create a text field 10 characters wide.
kiloTextField = new JTextField(10);

// Create a button with the caption "Calculate".
calcButton = new JButton("Calculate");

// Add an action listener to the button.
calcButton.addActionListener(new CalcButtonListener());

// Create a JPanel object and let the panel
// field reference it.
panel = new JPanel();

// Add the label, text field, and button
// components to the panel.
panel.add(messageLabel);
panel.add(kiloTextField);
panel.add(calcButton);
}

/**
CalcButtonListener is an action listener class for
the Calculate button.
*/

private class CalcButtonListener implements ActionListener
{
/**
The actionPerformed method executes when the user
clicks on the Calculate button.
@param e The event object.
*/

public void actionPerformed(ActionEvent e)
{
final double CONVERSION = 0.6214;
String input; // To hold the user's input
double miles; // The number of miles

// Get the text entered by the user into the
// text field.
input = kiloTextField.getText();

// For debugging, display the text entered, and
// its value converted to a double.
System.out.println("Reading " + input +
" from the text field.");
System.out.println("Converted value: " +
Double.parseDouble(input));

// Convert the input to miles.
miles = Double.parseDouble(input) * CONVERSION;

// Display the result.
JOptionPane.showMessageDialog(null, input +
" kilometers is " + miles + " miles.");

// For debugging, display a message indicating
// the application is ready for more input.
System.out.println("Ready for the next input.");
}
} // End of CalcButtonListener class

/**
The main method creates an instance of the
KiloConverter class, which displays
its window on the screen.
*/

public static void main(String[] args)
{
new KiloConverter();
}
}

Answer 1

KiloConverter.java:

// Code courtesy of Gaddis, Getting Started with Java, 6th Edition
import javax.swing.*; // Needed for Swing classes
import java.awt.event.*; // Needed for ActionListener Interface

/**
The KiloConverter class displays a JFrame that
lets the user enter a distance in kilometers. When
the Calculate button is clicked, a dialog box is
displayed with the distance converted to miles.
*/

public class KiloConverter extends JFrame
{
private JPanel panel; // To reference a panel
private JLabel messageLabel; // To reference a label
private JTextField kiloTextField; // To reference a text field
private JButton calcButton; // To reference a button
private final int WINDOW_WIDTH = 310; // Window width
private final int WINDOW_HEIGHT = 100; // Window height

/**
Constructor
*/

public KiloConverter()
{
// Set the window title.
setTitle("Kilometer Converter");

// Set the size of the window.
setSize(WINDOW_WIDTH, WINDOW_HEIGHT);

// Specify what happens when the close button is clicked.
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

// Build the panel and add it to the frame.
buildPanel();

// Add the panel to the frame's content pane.
add(panel);

// Display the window.
setVisible(true);
}

/**
The buildPanel method adds a label, text field, and
and a button to a panel.
*/

private void buildPanel()
{
// Create a label to display instructions.
messageLabel = new JLabel("Enter a distance " +
"in kilometers");

// Create a text field 10 characters wide.
kiloTextField = new JTextField(10);

// Create a button with the caption "Calculate".
calcButton = new JButton("Calculate");

// Add an action listener to the button.
calcButton.addActionListener(new CalcButtonListener());

// Create a JPanel object and let the panel
// field reference it.
panel = new JPanel();

// Add the label, text field, and button
// components to the panel.
panel.add(messageLabel);
panel.add(kiloTextField);
panel.add(calcButton);
}

/**
CalcButtonListener is an action listener class for
the Calculate button.
*/

private class CalcButtonListener implements ActionListener
{
/**
The actionPerformed method executes when the user
clicks on the Calculate button.
@param e The event object.
*/

public void actionPerformed(ActionEvent e)
{
final double CONVERSION = 0.6214;
String input; // To hold the user's input
double miles; // The number of miles

// Get the text entered by the user into the
// text field.
input = kiloTextField.getText();

// For debugging, display the text entered, and
// its value converted to a double.
System.out.println("Reading " + input +
" from the text field.");
System.out.println("Converted value: " +
Double.parseDouble(input));

// Convert the input to miles.
miles = Double.parseDouble(input) * CONVERSION;

// Display the result.
JOptionPane.showMessageDialog(null, input +
" kilometers is " + miles + " miles.");

// For debugging, display a message indicating
// the application is ready for more input.
System.out.println("Ready for the next input.");
}
} // End of CalcButtonListener class

/**
The main method creates an instance of the
KiloConverter class, which displays
its window on the screen.
*/

public static void main(String[] args)
{
new KiloConverter();
}
}

Output:

1). What is the window title?

Answer:

The title of the window in the above program is Kilometer Converter. setTitle("Kilometer Converter");

2). What type of object is calcButton?

Answer   calcButton is a JButton object.

3). What is the name of the JPanel variable in buildPanel?

Answer:The name of the JPanel variable in buildPanel is panel

4). What three components get added to the panel?

Answer:

The three components that get added to the panel are: JButton, JTextField, and JLabel

5). How does the program show its results: a message dialog, or on the console?

Answer:

The program shows it results in a Message dialog box

6). What variable is kiloTextField.getText() assigned to?

Answer:

The variable that is assigned to kiloTextField.getText() is "input"

7). What method is used to convert the input string to a Double?

Answer:

The method that is used to convert the input string to a Double is Double.parseDouble()

8). What method gets called to display the window? (What method makes the window visible?)

Answer:

The method that gets called to display the window is buildPanel();

9). What class does KiloConverter extend?

Answer:

The KiloConverter class extends JFrame Class.

10). What interface does calcButtonListener implement?

Answer:

The interface that calcButtonListener implements is: ActionListener