import static extension de.fhg.fokus.xtensions.objects.Objects.*
// ...
val person = new Person(null, null)
val first = person.getFirstName.recoverNull("John")
val last = person.getLastName.recoverNull[if(first == "John") "Doe" else "Unknown"]
println('''«first» «last»''')Objects
The class de.fhg.fokus.xtensions.objects.Objects provides a bunch of static extension methods
that can generally help with handling objects especially in null-safe navigation chains.
Recovering from null
To check if an object is null and provide a fallback object if the tested object is null,
the Objects class provides the extension functions recoverNull(T,T) and recoverNull(T,⇒T).
The Java 9 JDK provides functions the same functionality via the methods java.util.Objects#requireNonNullElse(T,T) and
java.util.Objects#requireNonNullElseGet(T, Supplier<? extends T>). This library provides API compatible
aliases for the recoverNull functions, so that a migration to Java 9 and the built-in methods is smooth.
Example:
In this example we initialize a person with first and last name set to null in both cases the recoverNull
functions have to provide a fallback object. Since first name defaults to "John" the last name will be evaluated
to "Doe".
Acting on non-null
The extension function ifNotNull will check a context object on null and if it is not will pass
the object to a consumer procedure. This can be handy at the end of null-safe navigation chains.
Example:
import static extension de.fhg.fokus.xtensions.objects.Objects.*
// ...
val person = // ...
preson?.getFirstName?.toFirstUpper.ifNotNull [
println(it)
]Cast or null
The Xtend operator as tests if an object instance of a given class and casts the objec
to this type if so. If not, the result of the operator will be null. Unfortunately this
cannot be simply used in a (null-safe) navigation chain. The asType extension method
wraps the same semantics in a function that can be called as part of a call chain.
Example:
val Vehicle v = // ...
v.asType(Car)?.getMake.ifNotNull [
println("Make: " + it)
]In the example the vehicle is casted to a Car and afterwards is either of type Car or null.
Therefore subsequent calls are performed via null-safe navigation. Since the object can now be
used as a car, methods of that type, such as getMake can be accessed.
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