Event Hookups and Adapters

Let’s get our juggler under control with the following steps:

We have completed a hookup between the button and the Juggler. When the button fires an action event, the juggling property of the Juggler is set to true.

Scroll around the source view and take a look at the code that NetBeans has generated to make this connection for us. Specifically, in the initComponents() method of our class, it has created an anonymous inner class to serve as the ActionListener for ActionEvents from our button (which it has named jButton1):

    jButton1.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jButton1ActionPerformed(evt);
        }
    });

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
        juggler1.setJuggling(true);
    }

Figure 22-4. Selecting a source event in the Connection Wizard

Figure 22-5. Specifying a target operation in the Connection Wizard

You’ll notice that most of the code that was written for us is shaded grey to indicate that it is autogenerated code and can’t be directly modified. The body of the private method is open, however, and we could modify it to perform arbitrary activities when the button is pushed. In NetBeans, the hookup is just a starting point.

This may all seem a little obtuse. After all, if we had made the Juggler an ActionListener in the first place, we would expect to hook it directly to the button. The use of adapters provides a great deal of flexibility, however, as we’ll see next.

To complete our example, click the Design button, then repeat the process, adding a second JButton labeled “Stop.” We could implement the Stop button in the same way that we did the Start button, by passing a specific value to the juggling method, but we’re going to try an alternative here. Click the Connection Wizard icon; select the Stop button and the Juggler as its target. Again, choose the actionPerformed method as the source, but this time, instead of selecting a property on the Juggler, click the Method Call radio button to see a list of available methods on the Juggler bean. Scroll all the way down and select the stopJuggling() method. Click Finish to complete the hookup, and look at the generated code if you wish. With this, we have seen an example of hooking up a source of action events to generate an arbitrary method call on a bean. (Of course, there is a startJuggling() method as well, which we could have used for the first button.)

Let’s look at one more interesting example, shown in Figure 22-6. Create a new file in our project as before, choosing Java GUI Forms from the Categories pane and JFrame Form in the File Types pane. Call this file LearningJava2.

Grab a Molecule bean and place it in the workspace. (The default BorderLayout maximizes its area if you place the bean in the center.) If you run the example now, you will see that by dragging the mouse within the image, you can rotate the model in three dimensions. Try changing the type of molecule by using the Properties pane: ethane is fun.^[45]

Let’s see what we can do with our molecule. Grab a Timer bean from the palette. Timer is a clock.^[46] Every so many milliseconds, Timer fires an event. The timer is controlled by an long property called delay, which determines the number of milliseconds between events. Timer is an “invisible” bean; it is not derived from a JComponent and doesn’t have a graphical appearance, just as an internal timer in an application doesn’t normally have a presence on the screen. NetBeans shows these invisible beans just like any other bean in the Navigator pane on the left. When you wish to select the Timer, click on it in the tree in the Navigator pane.

Let’s hook the Timer to our Molecule. Start the Connection Wizard and select the Timer (from the tree) and then the Molecule. Choose the Timer’s timerFired() event from the list (expand the folder to display it). Click Next and select the Method Call radio button. Find and select the rotateOnX() method and click Finish. Run the example. Now the Molecule should turn on its own every time it receives an event from the timer. Try changing the timer’s delay property. You can also hook the Timer to the Molecule’s rotateOnY() method. Use a different instance of Timer and, by setting different delay values, make it turn at different rates in each dimension. Fun!

Figure 22-6. The Molecule bean and the Timer