Introduction to Groovy - Learn Java for Web Development - page 416

Listing B-36 illustrates using the Java ternary and Elvis operators in Groovy.
Listing B-36. Using the Elvis Operator
def firstName = author.firstName == null ? "unknown" : author.firstName // Java ternary
def firstName2 = author.firstName ?: "unknown" // Groovy Elvis
In both cases, if author.firstName is null , then firstName is set to unknown . The author.firstName
fragment of the Elvis operator example is known as the expression . If the expression evaluates to
false or null , then the value after the colon is returned.
Safe Navigation/Dereference Operator
The safe navigation/dereference operator ( ?. ) is used to avoid null pointer exceptions. Consider the
situation where you have an Author object and you want to print the firstName . If the Author object is
null when you access the firstName property, you will get a NullPointerException (see Listing B-37).
Listing B-37. Using the Safe Navigation/Dereference Operator
class Author {
String firstName
String lastName
def printFullName = {
println "${firstName} ${lastName}"
}
}
Author author
println author.firstName
The code in Listing B-37 throws a NullPointerException . In Java, you add a null check this way:
if (author != null) {
println "Author FirstName = ${author.firstName}"
}
Listing B-38 illustrates how to add the null check using the safe navigation/dereference operator
in Groovy.
Listing B-38. Using the Safe Navigation/Dereference Operator
class Author {
String firstName
String lastName
def printFullName = {
println "${firstName} ${lastName}"
}
}
Author author
println "Author FirstName = ${author?.firstName}"