13.10. Centering a Display Using the FontMetrics Class

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Review Questions

Sections 12.3 “12.4

12.1	Which class is the root of the Java GUI component classes? Is a container class a subclass of Component ? Which class is the root of the Swing GUI component classes?
12.2	Explain the difference between AWT GUI components , such as java.awt.Button , and Swing components, such as javax.swing.JButton .
12.3	How do you create a frame? How do you set the size for a frame? How do you get the size of a frame? How do you add components to a frame? What would happen if the statements frame.setSize(400, 300) and frame.setVisible(true) were swapped in the MyFrameWithComponents class in Section 12.4.2, "Adding Components to a Frame"?
12.4	Determine whether the following statements are true or false: You can add a button to a frame. You can add a frame to a panel. You can add a panel to a frame. You can add any number of components to a panel or a frame. You can derive a class from JButton , JPanel , JFrame , or JApplet .
12.5	The following program is supposed to display a button in a frame, but nothing is displayed. What is the problem? 1 public class Test extends javax.swing.JFrame { 2 public Test() { 3 add( new javax.swing.JButton( "OK" )); 4 } 5 6 public static void main(String[] args) { 7 javax.swing.JFrame frame = new javax.swing.JFrame(); 8 frame.setSize( 100 , 200 ); 9 frame.setVisible( true ); 10 } 11 }
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12.6	Which of the following statements have syntax errors? Component c1 = new Component(); JComponent c2 = new JComponent(); Component c3 = new JButton(); JComponent c4 = new JButton(); Container c5 = new JButton(); c5.add(c4); Object c6 = new JButton(); c5.add(c6);

Section 12.5 Layout Managers

12.7	Why do you need to use layout managers? What is the default layout manager for a frame? How do you add a component to a frame?
12.8	Describe FlowLayout . How do you create a FlowLayout manager? How do you add a component to a FlowLayout container? Is there a limit to the number of components that can be added to a FlowLayout container?
12.9	Describe GridLayout . How do you create a GridLayout manager? How do you add a component to a GridLayout container? Is there a limit to the number of components that can be added to a GridLayout container?
12.10	Describe BorderLayout . How do you create a BorderLayout manager? How do you add a component to a BorderLayout container? Can you add multiple components in the same section?

Sections 12.6 “12.7

12.11	How do you create a color ? What is wrong about creating a Color using new Color(400, 200, 300) ? Which of the following two colors are darker , new Color(10, 0, 0) or new Color(200, 0, 0) ?
12.12	How do you create a font? How do you find all the available fonts on your system?

Section 12.8 Using Panels as Subcontainers

12.13	How do you create a panel with a specified layout manager?
12.14	What is the default layout manager for a JPanel ? How do you add a component to a JPanel ?
12.15	Can you use the setTitle method in a panel? What is the purpose of using a panel?
12.16	Since a GUI component class such as JButton is a subclass of Container , can you add components into a button?

Sections 12.9 “12.10

12.17	How do you set background color, foreground color, font, and tool tip text on a Swing GUI component? Why is the tool tip text not displayed in the following code? 1 import javax.swing.*; 2 3 public class Test extends JFrame { 4 private JButton jbtOK = new JButton( "OK" ); 5 6 public static void main(String[] args) { 7 // Create a frame and set its properties 8 JFrame frame = new Test(); 9 frame.setTitle( "Logic Error" ); [Page 422] 10 frame.setSize( 200 , 100 ); 11 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 12 frame.setVisible( true ); 13 } 14 15 public Test() { 16 jbtOK.setToolTipText( "This is a button" ); 17 add( new JButton( "OK" ) ); 18 } 19 }
12.18	Show the output of the following code: import javax.swing.*; public class Test { public static void main(String[] args) { JButton jbtOK = new JButton( "OK" ); System.out.println(jbtOK.isVisible()); JFrame frame = new JFrame(); System.out.println(frame.isVisible()); } }
12.19	How do you create an ImageIcon from the file image/us.gif in the class directory?
12.20	What happens if you add a button to a container several times, as shown below? Does it cause syntax errors? Does it cause runtime errors? JButton jbt = new JButton(); JPanel panel = new JPanel(); panel.add(jbt); panel.add(jbt); panel.add(jbt);
12.21	Will the following code display three buttons? Will the buttons display the same icon? 1 import javax.swing.*; 2 import java.awt.*; 3 4 public class Test extends JFrame { 5 public static void main(String[] args) { 6 // Create a frame and set its properties 7 JFrame frame = new Test(); 8 frame.setTitle( "ButtonIcons" ); 9 frame.setSize( 200 , 100 ); 10 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 11 frame.setVisible( true ); 12 } 13 14 public Test() { 15 ImageIcon usIcon = new ImageIcon( "image/usIcon.gif" ); 16 JButton jbt1 = new JButton(usIcon); 17 JButton jbt2 = new JButton(usIcon); 18 19 JPanel p1 = new JPanel(); 20 p1.add(jbt1); [Page 423] 21 22 JPanel p2 = new JPanel(); 23 p2.add(jbt2); 24 25 JPanel p3 = new JPanel(); 26 p2.add(jbt1); 27 28 add(p1, BorderLayout.NORTH); 29 add(p2, BorderLayout.SOUTH); 30 add(p3, BorderLayout.CENTER); 31 } 32 }
12.22	Can a border or an icon be shared by GUI components?