Java 7 for Absolute Beginners

CHAPTER 7 ■ WRITING A USER INTERFACE

private void createAndShowGUI() {

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.getContentPane()

.setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));

addAndArrangePanels(frame);

addMenu(frame);

frame.pack();

frame.setVisible(true);

}

public static void main(String[] args) {

MineSweeper mineSweeper = new MineSweeper();

mineSweeper.createAndShowGUI();

}

}

MineSweeper does the same things as the other Swing classes we've already written, and it does

quite a bit more, as you just saw. So let's step through exactly what it's doing. We'll start where you just

stopped: at the bottom, with the main method. As you learned in Chapter 1, “Writing Your First Java

Program,” the main method is the entry point for a program. Listing 7-5 shows the main method.

Listing 7-5. MineSweeper's main method

public static void main(String[] args) {

MineSweeper mineSweeper = new MineSweeper();

mineSweeper.createAndShowGUI();

}

The main method doesn't do much. It creates an instance of the MineSweeper class, which is a handy

way to avoid having to use nothing but static objects and methods throughout the class. Creating a new

object calls the constructor for that object's class. In the other classes we've seen so far, the constructors

have done nothing (and we've not coded them, relying on the default constructors for our objects). The

MineSweeper class, however, needs a true constructor. Listing 7-6 shows the constructor.

Listing 7-6. MineSweeper's constructor

public MineSweeper() {

helper = new MineSweeperHelper(this);

actionListener = new MineSweeperActionListener(this, helper);

mouseListener = new MineSweeperMouseListener(this, helper);

init();

}

The MineSweeper constructor first creates a helper object by instantiating (a fancy word for creating

an object) the MineSweeperHelper class. We have to do that first, so that we can pass the helper object to

our two listener objects. The next two lines create instances of the MineSweeperActionListener and

MineSweeperMouseListener classes. Those classes monitor the menu and the minefield (respectively) for

mouse clicks. We could have had those listeners here in the MineSweeper class (in fact, we originally had

that functionality in the MineSweeper class). Instead, we decided to have the MineSweeper class handle

just the user interface definition and push all the other tasks off to other classes. That's the kind of design