October 20, 2009

Just bought Core Java, Volume 1: Fundamentals Eighth Edition. Have read chapter 1 and 2 yet.

I met with a new method in chapter 2 today, which is named EventQueue.invokeLater, so look up more usage about it. Swing event handling code runs on a special thread known as the event dispatch thread. Most code that invoke Swing methods also runs on this thread. This is necessary because most Swing object methods are not "thread safe":invoking them from multiple threads risks thread interference or memory consistency errors. Some Swing component methods are labeled "thread safe" in the API specification; these can be safely invoked from any thread. All other Swing component methods must be invoked from the event dispatch thread. Programs that ignore this rule may function correctly most of the time, but are subject to unpredictable errors that are difficult to reproduce.

You can update the GUI components in any thread. However, their behavior is not always correct if you do so. Using invokeLater ensures that the GUI threads performs changes to the GUI and draws them correctly. For example, 

As we know, actionPerformed is called by EDT(short for Event Dispatch Thread), so you can update Swing component in this method directly. But if task in actionPerformed needs a long time, you may need a new thread and update related Swing component in this new created one. At this point, you should pay attention to the Swing component that you will manipulate. If the it is not "thread safe", you should use EventQueue.invokeLater!

Also, you can use SwingUtilities.isEventDispatchThread() to determin whether your code is running on EDT.

ps, here is an article about why we should not make Swing truly multithreaded. Have good day

 October 27, 2009

Have read chapter 3. 86 pages of this book have been read.

1. main function doesn't have any return statement, but you can use System.exit to return some state code to the OS

2. no unsigned type supported by Java

3. Java supports Chinese as variable name

4. Math.PI

5. s.equals(t) <==> s.compareTo(t) ==0

6. StringBuffer supports multiple threads, StringBuilder supports single threads

7. System.console().readPassword

8. BigInteger and BigDecimal