Java Magazine - July/August 2012

//rich client /

Listing 5 into the Stop WatchModel.java file. When you’re done, let’s move on to the next concept, which involves creating a custom binding.

Then, add the following lines to StopWatchNode.java:

import java.text.SimpleDateFormat; import javafx.beans.binding.StringBinding; import javafx.beans.property.IntegerProperty;

Step 3: Create a Custom Binding

As mentioned previously, the elapsed time value is formatted as an integer in Figure 6 but as a minutes:seconds:milliseconds string in Figure 3. This is accomplished by using a custom binding instead of the default binding provided by the SimpleIntegerProperty.

To implement a custom binding, our example defines a class named TimeStringBinding that extends the StringBinding class, which implements the Binding interface shown in Figure 1. You can see the code for the TimeStringBinding class in Listing 6.

As shown in Listing 6, to implement the custom binding we do the following:

■ ■ Define a constructor with the input arguments for the binding, calling the bind() method of the superclass.

■ ■ Override the computeValue() method, returning the desired output value for the binding.

To use this custom binding in the LazyInitEvalExercise project, comment out the following lines in the Stop WatchNode.java file:

elapsedTimeStrProperty.bind( new TimeStringBinding( stopWatchModel.elapsedMillis Property()

)

);

public class TimeStringBinding extends StringBinding { private SimpleDateFormat timeFormat = new SimpleDateFormat("mm:ss:SSS"); private IntegerProperty millis;

public TimeStringBinding(IntegerProperty millisArg) { super.bind(millisArg); millis = millisArg; }

JAVA IN ACTION

For extra credit, also replace the binding for the lapNode textProperty() in a similar manner so that it appears as shown in Figure 3.

Go ahead and run the LazyInitEvalExercise application to verify that the custom bindings cause the elapsed time and lap time values to be formatted as shown in Figure 3.

@Override protected String computeValue() { int elapsedInt = millis.get(); return timeFormat.format(elapsedInt); } }

Conclusion JavaFX 2 comes with numerous classes and interfaces that provide a powerful properties and bindings framework. You can optimize the evaluation of bindings and the initialization of properties by using the lazy approaches demonstrated above. In addition, you can define custom bindings when augmenting the default behavior of the bindings in the JavaFX 2 API as desired. </article>