13.6. Drawing Strings, Lines, Rectangles, and Ovals

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12.9. Common Features of Swing GUI Components

You have used several GUI components (e.g., JFrame , Container , JPanel , JButton , JLabel , JTextField ) in this chapter. Many more GUI components will be introduced in this book. It is important to understand the common features of Swing GUI components. The Component class is the root for all GUI components and containers. All Swing GUI components (except JFrame , JApplet , and JDialog ) are subclasses of JComponent , as shown in Figures 12.2 and 12.3. Figure 12.13 lists some frequently used methods in Component , Container , and JComponent for manipulating properties like font, color , size , tool tip text, and border.

Figure 12.13. All the Swing GUI components inherit the public methods from Component , Container , and JComponent .

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A tool tip is a text displayed on a component when you move the mouse on the component. It is often used to describe the function of a component.

You can set a border on any object of the JComponent class. Swing has several types of borders. To create a titled border, use new TitledBorder(String title) . To create a line border, use new LineBorder(Color color, int width) , where width specifies the thickness of the line.

Listing 12.7 is an example to demonstrate Swing common features. The example creates a panel p1 to hold three buttons (line 8) and a panel p2 to hold two labels (line 25). The background of the button jbtLeft is set to white (line 12), and the foreground of the button jbtCenter is set to green (line 13). The tool tip of the button jbtRight is set in line 14. Titled borders are set on panels p1 and p2 (lines 18, 36), and line borders are set on the labels (lines 32 “33).

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Listing 12.7. TestSwingCommonFeatures.java

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 1   import   java.awt.*; 2   import   javax.swing.*; 3   import   javax.swing.border.*; 4 5   public class   TestSwingCommonFeatures   extends   JFrame { 6   public   TestSwingCommonFeatures() { 7  // Create a panel to group three buttons  8 JPanel p1 =   new   JPanel(   new   FlowLayout(FlowLayout.LEFT,   2   ,   2   )); 9 JButton jbtLeft =   new   JButton(   "Left"   ); 10 JButton jbtCenter =   new   JButton(   "Center"   ); 11 JButton jbtRight =   new   JButton(   "Right"   ); 12  jbtLeft.setBackground(Color.WHITE);  13  jbtCenter.setForeground(Color.GREEN);  14  jbtRight.setToolTipText(   "This is the Right button"   );  15 p1.add(jbtLeft); 16 p1.add(jbtCenter); 17 p1.add(jbtRight); 18  p1.setBorder(   new   TitledBorder(   "Three Buttons"   ));  

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 19 20  // Create a font and a line border  21  Font largeFont =   new   Font(   "TimesRoman"   , Font.BOLD,   20   );  22  Border lineBorder =   new   LineBorder(Color.BLACK,   2   );  23 24  // Create a panel to group two labels  25 JPanel p2 =   new   JPanel(   new   GridLayout(   1   ,   2   ,   5   ,   5   )); 26 JLabel jlblRed =   new   JLabel(   "Red"   ); 27 JLabel jlblOrange =   new   JLabel(   "Orange"   ); 28 jlblRed.setForeground(Color.RED); 29  jlblOrange.setForeground(Color.ORANGE);  30  jlblRed.setFont(largeFont);  31 jlblOrange.setFont(largeFont); 32 jlblRed.setBorder(lineBorder); 33  jlblOrange.setBorder(lineBorder);  34 p2.add(jlblRed); 35 p2.add(jlblOrange); 36  p2.setBorder(   new   TitledBorder(   "Two Labels"   ));  37 38  // Add two panels to the frame  39 setLayout(   new   GridLayout(   2   ,   1   ,   5   ,   5   )); 40 add(p1); 41 add(p2); 42 } 43 44   public static void   main(String[] args) { 45  // Create a frame and set its properties  46 JFrame frame =   new   TestSwingCommonFeatures(); 47 frame.setTitle(   "TestSwingCommonFeatures"   ); 48 frame.setSize(   300   ,   150   ); 49 frame.setLocationRelativeTo(   null   );  // Center the frame  50 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 51 frame.setVisible(   true   ); 52 } 53 } 

Figure 12.14. The font, color, border, and tool tip text are set in the message panel.

Note

The same property may have different default values in different components. For example, the visible property in JFrame is false by default, but it is true in every instance of JComponent (e.g., JButton and JLabel ) by default. To display a JFrame , you have to invoke setVisible(true) to set the visible property true , but you don't have to set this property for a JButton or a JLabel , because it is already true . To make a JButton or a JLabel invisible, you may invoke setVisible(false) on. Please run the program and see the effect after inserting the following two statements in line 37:

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 jbtLeft.setVisible(   false   ); jlblRed.setVisible(   false   );