Chapter 12 - GUI Basics

Question 1

Swing components that don’t rely on native GUI are referred to as __

Answer 1

Lightweight components

Question 2

__ are referred to as heavyweight components.

Answer 2

AWT components

Question 3

Are all Swing GUI components lightweight?

Answer 3

No. Only the Swing components that don’t rely on native GUI are lightweight. Some Swing GUI components such as JFrame are heavyweight.

Question 4

Can every instance of Component be added to a container?

Answer 4

No. For example, a JFrame cannot be added to a container, because it is a top-level container.

Question 5

What is the correct order of these three statements?

1. frame.setLocationRelativeTo(null);
2. frame.setSize(100, 200);
3. frame.setVisible(true);

Answer 5

2 1 3

Question 6

Analyze the following code.

import java.awt.;
import javax.swing.;

public class Test  {
  public static void main(String[] args) {
    JFrame frame = new JFrame("My Frame");
    frame.add(new JButton("OK"));
    frame.add(new JButton("Cancel"));
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(200, 200);
    frame.setVisible(true);
  }
} 

Which button is displayed? Both, or one of them?

Answer 6

By default, the layout of the content pane in a JFrame is BorderLayout. Button OK is placed in the center of content pane, then button Cancel is placed in the same place. So you only can see button Cancel.

Question 7

How many frames are displayed?

import javax.swing.*;

public class Test  {
  public static void main(String[] args) {
    JFrame f1 = new JFrame("My Frame");
    JFrame f2 = f1;
    JFrame f3 = f2;
    f1.setVisible(true);
    f2.setVisible(true);
    f3.setVisible(true);
  }
}

Answer 7

Only 1. f1, f2 and f3 all reference to the same object.

Question 8

What is the most common statement for terminating the program when the frame is closed?

Answer 8

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

Question 9

Analyze the following code:

import javax.swing.*;

public class Test1 extends JFrame {
  public Test1() {
    JButton jbt1 = new JButton("OK");
    add(jbt1);
    jbt1 = new JButton("Not OK");
  }

  public static void main(String[] args) {
    JFrame frame = new Test1();
    frame.setSize(300, 300);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }
}

What does the program display?

Answer 9

The program displays a button with the text “OK”

Question 10

What layout manager should you use so that every component occupies the same size in the container?

Answer 10

GridLayout

Question 11

What should you use to position a Button within an application Frame so that the size of the Button is NOT affected by the Frame size?

Answer 11

FlowLayout

Question 12

Suppose a JFrame uses the GridLayout(2, 2). If you add six buttons to the frame, how many columns are displayed?

Answer 12

3

Question 13

Suppose a JFrame uses the GridLayout(0, 2). If you add six buttons to the frame, how many columns are displayed?

Answer 13

2

Question 14

Suppose a JFrame uses the GridLayout(2, 0). If you add six buttons to the frame, how many columns are displayed?

Answer 14

3

Question 15

To set a FlowLayout in panel jp, you can use the method __
A. jp.setLayout(new FlowLayout());
B. jp.setLayout(new FlowLayout(FlowLayout.CENTER));
C. jp.setLayout(new FlowLayout(FlowLayout.center));
D. jp.setLayout(FlowLayout());

Answer 15

A and B

Question 16

The default layout out of a contentPane in a JFrame is __

Answer 16

BorderLayout

Question 17

The default layout out of a JPanel is ___

Answer 17

FlowLayout

Question 18

To create a JPanel of the BorderLayout, use ___

Answer 18

JPanel p = new JPanel(new BorderLayout());

Question 19

The GUI API contains classes that can be classified into three groups. What are these three groups?

Answer 19

Component classes, container classes, and helper classes.

Question 20

What are some component classes?

Answer 20

Subclasses of Component are called component classes for creating the user interface. Component is the root class of all the user-interface classes including container classes, and JComponent is the root class of all the lightweight Swing components.

Question 21

What are some container classes?

Answer 21

JFrame, JPanel and JApplet are container classes, and used to contain other components.

Question 22

What does these statements print?
JButoon jbtOK = new JButton("OK");
System.out.println(jbtOK instanceof JButton);
System.out.println(jbtOK instanceof JComponent);
System.out.println(jbtOK instanceof Container);
System.out.println(jbtOK instanceof Component);
System.out.println(jbtOK instanceof Object);

Answer 22

They will all print “true”. It’s important to become familiar with the class inheritance hierarchy.

Question 23

What makes a container a “top-level” container?

Answer 23

If a container can be displayed without being embedded in another container, it’s a top-level container.

Question 24

What are some top-level containers?

Answer 24

Window, Frame, Dialog, JFrame, and JDialog

Question 25

Describe javax.swing.JFrame

Answer 25

JFrame is a top-level container for holding other Swing user-interface components in Java GUI applications.

Question 26

Describe javax.swing.JPanel

Answer 26

JPanel is an invisible container for grouping user-interface components. Panels can be nested. You can place panels inside another panel. JPanel is also often used as a canvas to draw graphics.

Question 27

Descibe javax.swingJDialog

Answer 27

JDialog is a popup window generally used as a temporary window to receive additional information from the user or to provide notification to the user.

Question 28

Is the java.awt.Color class a subclass of Component? What about the java.awt.LayoutManager class?

Answer 28

No. The helper classes, such as Graphics, Color, Font, FontMetrics, Dimension, and LayoutManager, are not subclasses of Component.

Question 29

Describe java.awt.LayoutManager

Answer 29

Every container contains a layout manager, which is an object responsible for laying out the the GUI components in the container.

Question 30

Why is creating a new class that extends JFrame preferred to creating frames directly by using JFrame?

Answer 30

1. Creating a GUI application means creating a frame, so it is natural to define a frame to extend JFrame.
2. The frame may be further extended to add new components or functions.
3. The class can be easily reused. For example, you can create multiple frames by creating multiple instances of the class.

Question 31

Why should you name all file names accessed inside programs, like image-file names, consistently, and using lowercase letters?

Answer 31

Because file names are not case sensitive in Windows, but they are case sensitive in UNIX. To enable programs to run on all platforms, you should name them consistently, using lowercase.