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Chapter 2. (Introduction) Swing Mechanics. Easy for reading, Click here!

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Chapter 2. (Introduction) Swing Mechanics. Easy for reading, Click here!

[ Return to Swing (Book) ]

Page: 4/14 

Previous Page Previous Page (3/14) - Next Page (5/14) Next Page
Subpages: 1. JComponent properties, size, and positioning 
2.  Event handling and dispatching 
3. Multithreading
4. Timers
5. AppContext service
6. Inside Timers & the TimerQueue
7. JavaBeans architecture
8. Fonts, Colors, Graphics and text
9. Using the Graphics clipping area
10. Graphics debugging
11. Painting and validation
12. Focus Management
13. Keyboard input, KeyStrokes, and Actions
14. SwingUtilities

2.4    Timers

class javax.swing.Timer

You can think of the Timer as a unique thread conveniently provided by Swing to fire ActionEvents at specified intervals (although this is not exactly how a Timer works internally, as we will see in section 2.6). ActionListeners can be registered to received these events just as we register them on buttons, and other components. To create a simple Timer that fires ActionEvents every second we can do something like the following:

import java.awt.event.*;

import javax.swing.*;

class TimerTest


  public TimerTest() {

    ActionListener act = new ActionListener() {

      public void actionPerformed(ActionEvent e) {

        System.out.println("Swing is powerful!!");



    Timer tim = new Timer(1000, act);


    while(true) {};


  public static void main( String args[] ) {

    new TimerTest();



First we set up an ActionListener to receive ActionEvents. Then we built a new Timer passing the time in milliseconds between events, the delay, and an ActionListener to send them to. Finally we call the Timer's start() method to turn it on. Since there is no GUI running for us the program will immediately exit, so we set up a loop to let the Timer continue to do its job indefinitely (we will explain why this is necessary in section 2.6).

When you run this code you will see "Swing is powerful!!" sent to standard output every second. Note that the Timer does not fire an event right when it is started. This is because its initial delay time defaults to the delay time passed to the constructor. If we want the Timer to fire an event right when it is started we would set the initial delay time to 0 using its setInitialDelay() method.

At any point we can call stop() to stop the Timer and start() to restart it (start() does nothing if it is already running). We can call restart() on a Timer to start the whole process over. The restart() method is just a shortcut way to call stop() and start() sequentually.

We can set a Timer's delay using the setDelay() method and tell it whether to repeat or not using the setRepeats() method. Once a Timer has been set to non-repeating it will fire only one action when started (or if it is currently running), and then it will stop.

The setCoalesce() method allows several Timer event postings to be combined (coalesced) into one. This can be useful under heavy loads when the TimerQueue (see below) thread doesn't have enough processing time to handle all its Timers.

Timers are easy to use and can often be used as convenient replacements for building our own threads. However, there is a lot more going on behind the scenes that deserves a bit of revealing. Before we are ready to look at how Timers work under the hood, we'll take a look at Swing's SecurityContext-to-AppContext service class mapping for applets, as well as how applications manage their service classes (also using AppContext). If you are not curious about how Swing manages the sharing of service classes behind the scenes, you will want to skip the next section. Although we will refer to AppContext from time to time, it is by no means necessary to understand the details.

[ Return to Swing (Book) ]

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Java Lessons

The Java Lesson 1:
What is Java?
The Java Lesson 2:
Anatomy of a simple Java program
The Java Lesson 3:
Identifiers and primitive data types
The Java Lesson 4:
Variables, constants, and literals
The Java Lesson 5:
Arithmetic operations, conversions, and casts
The Java Lesson 6:
Boolean expressions and operations
The Java Lesson 7:
Bitwise operations
The Java Lesson 8:
Flow control with if and else
The Java Lesson 9:
switch statements
The Java Lesson 10:
for, while, and do-while statements
The Java Lesson 11:
Using break and continue
The Java Lesson 12:
Class methods and how they are called
The Java Lesson 13:
Using the Math class
The Java Lesson 14:
Creating and calling custom class methods
The Java Lesson 15:
Overloading class methods
The Java Lesson 16:
An introduction to objects and object references
The Java Lesson 17:
The String class
The Java Lesson 18:
The StringBuffer class
The Java Lesson 19:
Initializing and processing arrays of primitives
The Java Lesson 20:
Initializing and processing arrays of objects
The Java Lesson 23:
Inheritance and overriding inherited methods
The Java Lesson 24:
abstract classes and polymorphism
The Java Lesson 25:
Interfaces, instanceof, and object conversion and casting
The Java Lesson 26:
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The Java Lesson 27:
The Component class
The Java Lesson 28:
Containers and simple layout managers
The Java Lesson 29:
The Color and Font classes
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Drawing geometric shapes
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Choice, List, and Checkbox controls
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Using the Scrollbar graphical control
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Menus and submenus
The Java Lesson 34:
An introduction to applets and the Applet class
The Java Lesson 35:
Essential HTML to launch an applet and pass it parameters
The Java Lesson 36:
Mouse event processing
Java Lesson 37:
Menus and submenus
Java Lesson 38:
The WindowListener interface and the WindowAdapter class
Java Lesson 39:
An introduction to GridBagLayout
Java Lesson 40:
An introduction to the Java Collections API
Java Lesson 41:
Exception handling with try, catch, and finally blocks
Java Lesson 42:
Claiming and throwing exceptions
Java Lesson 43:
Multithreading, the Thread class, and the Runnable interface
Java Lesson 44:
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Low-level and high-level stream classes
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