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This commit is contained in:
Sam Brannen
2024-02-11 15:34:20 +01:00
parent f295def2a8
commit 347d085020
8 changed files with 76 additions and 30 deletions
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4
framework-docs/modules/ROOT/pages/core/expressions/language-ref/collection-projection.adoc
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@@ -13,7 +13,7 @@ Java::
+
[source,java,indent=0,subs="verbatim,quotes",role="primary"]
----
// evaluates to ["SmilJan", "Idvor"]
// evaluates to ["Smiljan", "Idvor"]
List placesOfBirth = parser.parseExpression("members.![placeOfBirth.city]")
.getValue(societyContext, List.class);
----
@@ -22,7 +22,7 @@ Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
----
// evaluates to ["SmilJan", "Idvor"]
// evaluates to ["Smiljan", "Idvor"]
val placesOfBirth = parser.parseExpression("members.![placeOfBirth.city]")
.getValue(societyContext) as List<*>
----

42
framework-docs/modules/ROOT/pages/core/expressions/language-ref/operator-safe-navigation.adoc
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@@ -1,12 +1,14 @@
[[expressions-operator-safe-navigation]]
= Safe Navigation Operator
The safe navigation operator is used to avoid a `NullPointerException` and comes from
the https://www.groovy-lang.org/operators.html#_safe_navigation_operator[Groovy]
language. Typically, when you have a reference to an object, you might need to verify that
it is not null before accessing methods or properties of the object. To avoid this, the
safe navigation operator returns null instead of throwing an exception. The following
example shows how to use the safe navigation operator:
The safe navigation operator (`?`) is used to avoid a `NullPointerException` and comes
from the https://www.groovy-lang.org/operators.html#_safe_navigation_operator[Groovy]
language. Typically, when you have a reference to an object, you might need to verify
that it is not `null` before accessing methods or properties of the object. To avoid
this, the safe navigation operator returns `null` instead of throwing an exception.
The following example shows how to use the safe navigation operator for property access
(`?.`).
[tabs]
======
@@ -20,13 +22,18 @@ Java::
Inventor tesla = new Inventor("Nikola Tesla", "Serbian");
tesla.setPlaceOfBirth(new PlaceOfBirth("Smiljan"));
String city = parser.parseExpression("placeOfBirth?.city").getValue(context, tesla, String.class);
System.out.println(city); // Smiljan
// evaluates to "Smiljan"
String city = parser.parseExpression("placeOfBirth?.city") // <1>
.getValue(context, tesla, String.class);
tesla.setPlaceOfBirth(null);
city = parser.parseExpression("placeOfBirth?.city").getValue(context, tesla, String.class);
System.out.println(city); // null - does not throw NullPointerException!!!
// evaluates to null - does not throw NullPointerException
city = parser.parseExpression("placeOfBirth?.city") // <2>
.getValue(context, tesla, String.class);
----
<1> Use safe navigation operator on non-null `placeOfBirth` property
<2> Use safe navigation operator on null `placeOfBirth` property
Kotlin::
+
@@ -38,14 +45,17 @@ Kotlin::
val tesla = Inventor("Nikola Tesla", "Serbian")
tesla.setPlaceOfBirth(PlaceOfBirth("Smiljan"))
var city = parser.parseExpression("placeOfBirth?.city").getValue(context, tesla, String::class.java)
println(city) // Smiljan
// evaluates to "Smiljan"
var city = parser.parseExpression("placeOfBirth?.city") // <1>
.getValue(context, tesla, String::class.java)
tesla.setPlaceOfBirth(null)
city = parser.parseExpression("placeOfBirth?.city").getValue(context, tesla, String::class.java)
println(city) // null - does not throw NullPointerException!!!
// evaluates to null - does not throw NullPointerException
city = parser.parseExpression("placeOfBirth?.city") // <2>
.getValue(context, tesla, String::class.java)
----
<1> Use safe navigation operator on non-null `placeOfBirth` property
<2> Use safe navigation operator on null `placeOfBirth` property
======