Java 7 for Absolute Beginners

CHAPTER 7 ■ WRITING A USER INTERFACE

After the constructor and the init method are done setting up the game, the main method passes

control to the next method in the chain of execution: createAndShowGUI. Listing 7-8 shows the

createAndShowGUI method.

Listing 7-8. MineSweeper's createAndShowGUI method

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);

}

The createAndShowGUI method sets up and shows the JFrame object. Remember that a JFrame object

is a window. So we define the details of the program's window and then show it. Let's take it line by line

from here. The first line indicates that closing the window should also exit the program (stopping a

program and removing it from the operating system's list of running programs is often called “exiting a

program”). The second line sets the layout. In this case, it uses a BoxLayout object that places controls in

a line vertically. Notice that we have to get the content pane to be able to set the layout. Next, we pass

execution (that is, the current work being done by the program) to the addAndArrangePanels method

(which we get to next). When that's done, execution returns to this method. Then, we pass execution to

yet another method called addMenu. Notice that both of those methods take the JFrame object as

argument, which tells us that those methods do more of the work of setting up the window. In fact, they

do most of that work. Finally, we get to the last two lines, which directly affect the JFrame object. The line

that calls the pack method on the JFrame object (that is, the frame.pack(); line) tells the JVM to organize

all the controls in the JFrame object. The last line calls the setVisible method on the JFrame object,

which is Java's way of saying to make the window visible to the user. You can keep windows in memory

and make them visible or invisible. This gives better performance than re-specifying a window when you

need to hide a window.

Now let's look at the addAndArrangePanels method, which appears in listing 7-9.

Listing 7-9. MineSweeper's addAndArrangePanels method

private void addAndArrangePanels(JFrame frame) {

Border paddingBorder = BorderFactory.createEmptyBorder(5,5,5,5);

JPanel controlPanel = new JPanel();

minesFoundLabel.setBorder(paddingBorder);

minesFoundLabel.setAlignmentX(Component.LEFT_ALIGNMENT);

minesRemainingLabel.setAlignmentX(Component.RIGHT_ALIGNMENT);

minesRemainingLabel.setBorder(paddingBorder);

minesRemainingLabel.setText("Remaining: " + mineField.getMinesRemaining());

controlPanel.add(minesFoundLabel);

controlPanel.add(minesRemainingLabel);

GridLayout gridLayout = new GridLayout(1,2);

controlPanel.setLayout(gridLayout);