MULTITHREADING AND PARALLEL PROGRAMMING - Introduction to Java Programming: Comprehensive Version - page 1106

42 // Create a scene and place it in the stage
43 Scene scene = new Scene(pane, 200 , 50 );
44 primaryStage.setTitle( "FlashText" ); // Set the stage title
45 primaryStage.setScene(scene); // Place the scene in the stage
46 primaryStage.show(); // Display the stage
47 }
48 }

The program creates a Runnable object in an anonymous inner class (lines 17-40). This
object is started in line 40 and runs continuously to change the text in the label. It sets a text
in the label if the label is blank (line 23) and sets its text blank (line 25) if the label has a text.
The text is set and unset to simulate a flashing effect.
JavaFX GUI is run from the JavaFX application thread . The flashing control is run from
a separate thread. The code in a nonapplication thread cannot update GUI in the application
thread. To update the text in the label, a new Runnable object is created in lines 27-32.
Invoking Platform.runLater(Runnable r) tells the system to run this Runnable object
in the application thread.
The anonymous inner classes in this program can be simplifed using lambda expressions
as follows:

JavaFX application thread

Platform.runLater

new Thread(() -> { // lambda expression
try {
while ( true ) {
if (lblText.getText().trim().length() == 0 )
text = "Welcome" ;
else
text = "" ;

Platform.runLater(() -> lblText.setText(text)); // lambda exp

Thread.sleep( 200 );
}
}
catch (InterruptedException ex) {
}
}).start();

30.9

✓ ✓

What causes the text to flash?

Check

30.10

Point

Is an instance of FlashText a runnable object?

30.11

What is the purpose of using Platform.runLater ?

30.12

Can you replace the code in lines 27-32 using the following code?

Platform.runLater(e -> lblText.setText(text));
30.13

What happens if line 34 ( Thread.sleep(200) ) is not used?

30.6 Thread Pools
A thread pool can be used to execute tasks efficiently.

Key
Point

In Section 30.3, Creating Tasks and Threads, you learned how to define a task class by imple-
menting java.lang.Runnable , and how to create a thread to run a task like this:

Runnable task = new TaskClass(task);
new Thread(task).start();