Sun java tutorial swing addActionListener code

[Tom Never]

I am reading the sun tutorial and I don't see in this code where the 2nd addActionListener is in the code for both the enter and button. They write in the tutorial:

We want to perform the conversion when the user clicks the button or presses Enter in the text field. To do so, we add an action event listener to the convertTemp button and tempCelsius text field.

convertTemp.addActionListener(this);
tempCelsius.addActionListener(this);
...

But I don't see it in the code. It works, for both button and enter, but where is it in the code? Thanks, Tom

[I]/**
 * CelsiusConverter.java is a 1.4 application that 
 * demonstrates the use of JButton, JTextField and
 * JLabel.  It requires no other files.
 */
 
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class CelsiusConverter implements ActionListener {
    JFrame converterFrame;
    JPanel converterPanel;
    JTextField tempCelsius;
    JLabel celsiusLabel, fahrenheitLabel;
    JButton convertTemp;
 
    public CelsiusConverter() {
        //Create and set up the window.
        converterFrame = new JFrame("Convert Celsius to Fahrenheit");
        converterFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        converterFrame.setSize(new Dimension(120, 40));
 
        //Create and set up the panel.
        converterPanel = new JPanel(new GridLayout(2, 2));
 
        //Add the widgets.
        addWidgets();
 
        //Set the default button.
        converterFrame.getRootPane().setDefaultButton(convertTemp);
 
        //Add the panel to the window.
        converterFrame.getContentPane().add(converterPanel, BorderLayout.CENTER);
 
        //Display the window.
        converterFrame.pack();
        converterFrame.setVisible(true);
    }
 
    /**
     * Create and add the widgets.
     */
    private void addWidgets() {
        //Create widgets.
        tempCelsius = new JTextField(2);
        celsiusLabel = new JLabel("Celsius", SwingConstants.LEFT);
        convertTemp = new JButton("Convert");
        fahrenheitLabel = new JLabel("Fahrenheit", SwingConstants.LEFT);
 
        //Listen to events from the Convert button.
        [B]convertTemp.addActionListener(this);[/B]
 
        //Add the widgets to the container.
        converterPanel.add(tempCelsius);
        converterPanel.add(celsiusLabel);
        converterPanel.add(convertTemp);
        converterPanel.add(fahrenheitLabel);
        
        celsiusLabel.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
        fahrenheitLabel.setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
    }
 
    public void actionPerformed(ActionEvent event) {
        //Parse degrees Celsius as a double and convert to Fahrenheit.
        int tempFahr = (int)((Double.parseDouble(tempCelsius.getText()))
                             * 1.8 + 32);
        fahrenheitLabel.setText(tempFahr + " Fahrenheit");
    }
 
    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);
 
        CelsiusConverter converter = new CelsiusConverter();
    }
 
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}[/

I]

[Ernest Friedman-Hill]

You're not going crazy; the writeup doesn't match the code. In the code, they only add the event handler to the button, not to the JTextField. But they also do this:

converterFrame.getRootPane().setDefaultButton(convertTemp);

That ensures that any unhandled "Enter" presses will filter up to the RootPane, which will dispatch them as ActionEvents to the given default button. Note how when you press Enter, the button flashes. So the JTextField isn't handling the Enter presses at all!

Maybe they wrote it one way, changed it, and didn't update the description!

[Tom Never]

Thanks. I'm still learning my way around packages/api documentation. It's amazing what they don't tell you.