Operators
In general all operators supported in Java are identical in Groovy. Groovy goes a step further by allowing you to customize behavior of operators on Groovy types.
Arithmetic and Conditional Operators
See Operator Overloading for a list of the common operators that Groovy supports.
In addition, Groovy supports the ! (not) operator as follows:
def expression = false assert !expression
For more details about how expressions are corced to a boolean value, see: Groovy Truth.
Collection-based Operators
Spread Operator (*.)
The Spread Operator is used to invoke an action on all items of an aggregate object. It is equivalent to calling the collect method like so:
parent*.action //equivalent to:
parent.collect{ child -> child?.action }
The spread operator may be used a method call or property access, and returns a list of the items returned from each child call. So you may effectively override the spread operator by implementing a custom collect method.
Object-Related Operators
- invokeMethod and get/setProperty (.)
- Method Reference (.&)
- 'as' - "manual coercion" - asType(t) method
- Groovy == ( equals() ) behavior.
- "is" for identity
- The instanceof operator (as in Java)
Other Operators
- getAt() and setAt() for the subscript operator (e.g. foo[1])
- Range Operator (..) - see Collections#Collections-Ranges
- Membership Operator (in)
Elvis Operator (?:)
The "Elvis operator" is a shortening of Java's ternary operator. One instance of where this is handy is for returning a 'sensible default' value if an expression resolves to false or null. A simple example might look like this:
def gender = user.male ? "male" : "female" //traditional ternary operator usage def displayName = user.name ?: "Anonymous" //more compact Elvis operator
Safe Navigation Operator (?.)
The Safe Navigation operator is used to avoid a NullPointerException. 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 will simply return null instead of throwing an exception, like so:
def user = User.find( "admin" ) //this might be null if 'admin' does not exist def streetName = user?.address?.street //streetName will be null if user or user.address is null - no NPE thrown
