Properties and Bindings - JavaFX 8: A Definitive Guide to Building Desktop, Mobile, and Embedded Java Clients - page 168

Notice how the 13 lines of code and 12 intermediate variables used in Listing 4-5 to build up the area binding are
reduced to the 7 lines of code with no intermediate variables used in Listing 4-6. We also used the Bindings.format()
method to build up a StringExpression object called output . There are two overloaded Bindings.format() methods
with signatures:

StringExpression format(Locale locale, String format, Object... args)
StringExpression format(String format, Object... args)

They work similarly to the corresponding String.format() methods in that they format the values args
according to the format specification format and the Locale locale , or the default Locale . If any of the args is an
ObservableValue , its change is reflected in the StringExpression .
When we run the program in Listing 4-6, the following output is printed to the console:

For A(0,0), B(6,0), C(4,3), the area of triangle ABC is 9.0
For A(1,0), B(2,2), C(0,1), the area of triangle ABC is 1.5

Next we unravel the mystery of the When class and the role it plays in constructing bindings that are essentially
if/then/else expressions. The When class has a constructor that takes an ObservableBooleanValue argument:
public When(ObservableBooleanValue b)
It has the following 11 overloaded then() methods.

When.NumberConditionBuilder then(ObservableNumberValue n)
When.NumberConditionBuilder then(double d)
When.NumberConditionBuilder then(float f)
When.NumberConditionBuilder then(long l)
When.NumberConditionBuilder then(int i)
When.BooleanConditionBuilder then(ObservableBooleanValue b)
When.BooleanConditionBuilder then(boolean b)
When.StringConditionBuilder then(ObservableStringValue str)
When.StringConditionBuilder then(String str)
When.ObjectConditionBuilder<T> then(ObservableObjectValue<T> obj)
When.ObjectConditionBuilder<T> then(T obj)

The type of object returned from the then() method depends on the type of the argument. If the argument is a
numeric type, either observable or unobservable, the return type is a nested class When.NumberConditionBuilder .
Similarly, for Boolean arguments, the return type is When.BooleanConditionBuilder ; for string arguments,
When.StringConditionBuilder ; and for object arguments, When.ObjectConditionBuilder .
These condition builders in turn have the following otherwise() methods.

When.NumberConditionBuilder • For

NumberBinding otherwise(ObservableNumberValue n) •

DoubleBinding otherwise(double d) •

NumberBinding otherwise(float f) •

NumberBinding otherwise(long l)

•

NumberBinding otherwise(int i) •