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Questions and Exercises: Learning Swing by Example - Java Tutorial 5.0 英文版

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Trail: Creating a GUI with JFC/Swing
Lesson: Learning Swing by Example

Questions and Exercises: Learning Swing by Example

Questions

Question 1: On what thread should GUIs be created, to guarantee thread safety?
Answer 1: The event-dispatching thread.

Question 2: Why should you be careful to minimize the time spent in event-handler code?
Answer 2: Painting code also executes in the event-dispatching thread. Therefore, event-handling code should execute quickly so that the program抯 GUI stays responsive. If an event takes too long to execute, the GUI will freeze--that is, it won抰 repaint or respond to mouse clicks.

Question 3: What is the purpose of the setLabelFor method?
Answer 3: The setLabelFor method provides a hint to assistive technologies, such as screen readers, that the label describes a particular component.

Question 4: What is the content pane?
Answer 4: The content pane is the main container in JApplet, JDialog, and JFrame objects.

Question 5: Describe the three code segments that must be implemented for an event handler.
Answer 5:

  1. In the declaration for the event handler class, one line of code specifies that the class either implements a listener interface or extends a class that implements a listener interface. For example: 
    public class MyClass implements ActionListener {
  2. Another line of code registers an instance of the event handler class as a listener on one or more components. For example: 
    someComponent.addActionListener(instanceOfMyClass);
  3. The event handler class has code that implements the methods in the listener interface. For example: 
    public void actionPerformed(ActionEvent e) { 
    ...//code that reacts to the action... 
}

Question 6: Which text component is best suited for controlling the format of a single line of user-entered text?
Answer 6: JFormattedTextField

Question 7: What is lazy image loading and why would you use it?
Answer 7: With lazy image loading you only load images as they are needed. By loading images as needed, you reduce the application's initialization time; however, the downside is that the user may notice a delay as an image is loaded.

Exercises

Question 1: Write the code that creates a label displaying the following text, with the italics and font size as shown in this screenshot:


Answer 1: Here's the code that sets the label text: 
private static String labelText = 
        "<html>The <em>last</em%gt; word is <font size=+2>big</font>.</html>";
For the full code, see Test1 ( in a .java source file).

Question 2: Convert the LunarPhases example to use radio buttons instead of a combo box.
Answer 2: See LunarPhasesRB.

Question 3: Add a Show Dialog check box to the VoteDialog example so that the dialogs are shown only if this check box is selected.
Answer 3:


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