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The output from the above code is: static_propertyMissing foo static_methodMissing foo null static_propertyMissing bar null $static_methodMissing works slightly differently from methodMissing in that if there’s no method with the specified name, it looks for a closure property with that name to invoke as if it were a method. This results in a message about a missing foo property and a missing foo method. Operators Groovy adds several operators to the standard set of Java operators. Null-Safe Dereference The most commonly used is the null-safe dereference operator, ?., which lets you avoid a NullPointerException when calling a method or accessing a property on a null object. It’s especially useful in a chain of such accesses where a null value could occur at some point in the chain. For example, you can safely call: String name = person?.organization?.parent?.name and if person, person.organization, or organization.parent are null, then null is returned as the expression value. The Java alternative is a lot more verbose: Elvis String name = null; if (person != null) { if (person.getOrganization() != null) { if (person.getOrganization().getParent() != null) { name = person.getOrganization().getParent().getName(); } } } The Elvis operator, ?:, lets you condense ternary expressions; these two are equivalent: and: String name = person.name ?: defaultName String name = person.name ? person.name : defaultName 26 | Chapter 1: Introduction to Groovy
They both assign the value of person.name to the name variable if it is “Groovy true” (in this case, not null and has nonzero length, because it’s a string), but using the Elvis operator is more DRY. Spread The spread operator, *., is convenient when accessing a property or calling a method on a collection of items and collecting the results. It’s essentially a shortcut for the collect GDK method, although it’s limited to accessing one property or calling one method, for example: def numbers = [1.41421356, 2.71828183, 3.14159265] assert [1, 2, 3] == numbers*.intValue() Spaceship The spaceship operator is useful when comparing values; for example, when im‐ plementing the compareTo method of the Comparable interface. For example, given a POGO where you want to sort by two properties, the spaceship operator makes the implementation very compact: class Person implements Comparable { String firstName String lastName } int compareTo(Person p) { lastName p?.lastName ?: firstName p?.firstName } String toString() { "$firstName $lastName" } def zakJones = new Person(firstName: 'Zak', lastName: 'Jones') def jedSmith = new Person(firstName: 'Jed', lastName: 'Smith') def alJones = new Person(firstName: 'Al', lastName: 'Jones') def persons = [zakJones, jedSmith, alJones] assert [alJones, zakJones, jedSmith] == persons.sort(false) because the operator returns –1 if the left is less than the right, 0 if they’re equal, and 1 if the right is more than the left. So when the first expression (lastName p?.last Name) is nonzero, its value is used as the return value and the sort is done by last Name. If the last names match, then the Elvis operator kicks in and the second expression (firstName p?.firstName) is used to do a secondary sort by firstName. You can also use the operator for one-off sorting regardless of whether the items are Comparable, for example: Operators | 27
Page 2 and 3: Want to read more? Spreading the kn
Page 4 and 5: Table of Contents Preface. . . . .
Page 6 and 7: Data Validation 69 Custom Validatio
Page 8 and 9: Custom Configurations 148 Mapping V
Page 10 and 11: Monitoring and the Cloud Foundry UI
Page 12 and 13: standalone utility applications. Ju
Page 14 and 15: Collections and Maps Creating and p
Page 16 and 17: The default scope for classes, fiel
Page 18 and 19: Decompiling with JD-GUI I highly re
Page 20 and 21: println hello.getClass().superclass
Page 22 and 23: } }; This can be invoked from Groov
Page 24 and 25: You’ve already seen how property
Page 26 and 27: with: String s = someMethod(...) if
Page 28 and 29: or you could just skip the whole fo
Page 30 and 31: Using a StringBuilder (the preferre
Page 32 and 33: Every Groovy class implements the g
Page 34 and 35: You called add with args [2, 3] nul
Page 38 and 39: assert [alJones, jedSmith, zakJones
Page 40 and 41: } def leftShift(Person child) { chi
Page 42 and 43: def strings = [] but when the right
Page 44 and 45: See the Groovy 2.0 release notes an

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