Groovy Syntax Overview
This tutorial series introduces the syntax of the Groovy programming language. Groovy’s syntax derives from Java’s syntax, but it is enhanced by specific types and allows certain simplifications.
6. Booleans
A boolean is a special data type used to represent truth values: true and false. Use this data type as a simple flag for tracking true/false conditions.
Boolean values can be stored in variables just like any other data type:
def myBooleanVariable = true
boolean untypedBooleanVar = false
booleanField = true
true and false are the only two primitive boolean values. However, logical operators can be used to express more complex boolean expressions.
In addition, Groovy has special rules (usually called Groovy Truth) for coercing non-boolean objects to the boolean type.
6.1 Groovy Truth
Groovy determines whether an expression is true or false by applying the rules given below.
6.1.1 Boolean Expressions
If the boolean value is true, it is true.
assert true
assert !false
6.1.2 Collections and Arrays
Non-empty collections and arrays are true.
assert [1, 2, 3]
assert ![]
6.1.3 Matchers
A matcher is true if it has at least one match.
assert ('a' =~ /a/)
assert !('a' =~ /b/)
6.1.4 Iterators and Enumerations
Iterators and enumerations that contain elements are coerced to true.
assert [0].iterator()
assert ![].iterator()
Vector v = [0] as Vector
Enumeration enumeration = v.elements()
assert enumeration
enumeration.nextElement()
assert !enumeration
6.1.5 Maps
Non-empty maps are coerced to true.
assert ['one' : 1]
assert ![:]
6.1.6 Strings
Non-empty strings, GStrings and CharSequences are true.
assert 'a'
assert !''
def nonEmpty = 'a'
assert "$nonEmpty"
def empty = ''
assert !"$empty"
6.1.7 Numbers
Non-zero numbers are true.
assert 1
assert 3.5
assert !0
6.1.8 Object References
Non-null object references are true.
assert new Object()
assert !null
6.1.9 Customising Truth with the asBoolean() Method
To customise whether Groovy converts an object to true or false, you can implement the asBoolean() method:
class Color {
String name
boolean asBoolean(){
name == 'green' ? true : false
}
}
Groovy will call this method to coerce the object to a boolean, for example:
assert new Color(name: 'green')
assert !new Color(name: 'red')