/*
 * SwingApplication.java is a 1.4 example that requires
 * no other files.
 */
import javax.swing.*;         
import java.awt.*;
import java.awt.event.*;

public class SwingApplication implements ActionListener {
    private static String labelPrefix = "Number of button clicks: ";
    private int numClicks = 0;
    final JLabel label = new JLabel(labelPrefix + "0    ");

    //Specify the look and feel to use.  Valid values:
    //null (use the default), "Metal", "System", "Motif", "GTK+"
    final static String LOOKANDFEEL = null;   //Mark 1

    public Component createComponents() {　//Component类与JFrame类的层次关系？？？
        JButton button = new JButton("I'm a Swing button!");
        button.setMnemonic(KeyEvent.VK_I);
        button.addActionListener(this);
        label.setLabelFor(button);//That code exists solely as a hint to assistive technologies,

                                                      //such as screen readers, that the label describes the button.

                                                       //what is the sceen readers??

        /*
         * An easy way to put space between a top-level container  //为什么不能直接加上了？？？非得先加到JPane上么？？？ ＮＯＴＥ3
         * and its contents is to put the contents in a JPanel
         * that has an "empty" border.
         */
        JPanel pane = new JPanel(new GridLayout(0, 1));　　
        pane.add(button);
        pane.add(label);
        pane.setBorder(BorderFactory.createEmptyBorder(
                                        30, //top
                                        30, //left
                                        10, //bottom
                                        30) //right
                                        );

        return pane;
    }

    public void actionPerformed(ActionEvent e) {
        numClicks++;
        label.setText(labelPrefix + numClicks);
    }

    private static void initLookAndFeel() {    //NOTE 2
        String lookAndFeel = null;

        if (LOOKANDFEEL != null) {　　//LOOKANDFEEL在哪定义???　见上面标注1

                                                                  //不过我不明白，既然LOOKANDFEEL已定义为final,且同时也赋值为null　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　那还有什么可比较的呢？？？？？
            if (LOOKANDFEEL.equals("Metal")) {
                lookAndFeel = UIManager.getCrossPlatformLookAndFeelClassName();
            } else if (LOOKANDFEEL.equals("System")) {
                lookAndFeel = UIManager.getSystemLookAndFeelClassName();
            } else if (LOOKANDFEEL.equals("Motif")) {
                lookAndFeel = "com.sun.java.swing.plaf.motif.MotifLookAndFeel";
            } else if (LOOKANDFEEL.equals("GTK+")) { //new in 1.4.2
                lookAndFeel = "com.sun.java.swing.plaf.gtk.GTKLookAndFeel";
            } else {
                System.err.println("Unexpected value of LOOKANDFEEL specified: "
                                   + LOOKANDFEEL);
                lookAndFeel = UIManager.getCrossPlatformLookAndFeelClassName();
            }

            try {
                UIManager.setLookAndFeel(lookAndFeel);
            } catch (ClassNotFoundException e) {
                System.err.println("Couldn't find class for specified look and feel:"
                                   + lookAndFeel);
                System.err.println("Did you include the L&F library in the class path?");
                System.err.println("Using the default look and feel.");
            } catch (UnsupportedLookAndFeelException e) {
                System.err.println("Can't use the specified look and feel ("
                                   + lookAndFeel
                                   + ") on this platform.");
                System.err.println("Using the default look and feel.");
            } catch (Exception e) {
                System.err.println("Couldn't get specified look and feel ("
                                   + lookAndFeel
                                   + "), for some reason.");
                System.err.println("Using the default look and feel.");
                e.printStackTrace();
            }
        }
    }

    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Set the look and feel.
        initLookAndFeel();  //See NOTE 2

        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);

        //Create and set up the window.
        JFrame frame = new JFrame("SwingApplication");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        SwingApplication app = new SwingApplication();  //一见到这个心里边得先绕个弯儿呀，总得先回想下，这　是调用此类中那个默认的构造方法，//另外问题：像现在这种情况下，怎么根据上下文来确定字体、颜色等属性呢？？？？
        Component contents = app.createComponents();  //第一次见这样用某一方法的返回类型来定义对象。

                                                                                                  //createComponents方法返回一个JPane类，而JPane类为Component的子类。可行！！！
        frame.getContentPane().add(contents, BorderLayout.CENTER);　//接上面的ＮＯＴＥ3，是不是在JFrame上加了一层JPane后，就可以很方便的应用 BorderLayout.CENTER了这样的功能设置了呢???

        //Display the window.
        frame.pack(); //现在这个pack()方法的详细描述，它是根据哪些因素来

               //类库的解释为：Causes this Window to be sized to fit the preferred size and layouts of its subcomponents. If the window and/or its owner are not yet displayable, both are made displayable before calculating the preferred size. The Window will be validated after the preferredSize is calculated.

                  //在这儿perferred的标准有哪些？？？？
        frame.setVisible(true);
    }

    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();
            }
        });
    }
}