These notes are extracted from Appendix C.6 of Groovy Programming. (See Recommended Reading).

The logical operators are given in Table 1. The logical and operator (represented as &&) and the logical or operator are binary operators. They are applied to a pair of Boolean values and produce a Boolean result. The logical negation operator ! (not) is a unary operator applied to a single Boolean value that delivers a Boolean result.

Table 1 Logical Operators

The effect of applying these operators is shown in Table 2.

Table 2 Evaluation of Logical Expressions (Truth Tables)

If you are familiar with hardware logic, you may be surprised to see “don't care” for the value of Q in the cases P && Q when P is false and P || Q when P is true. This is because Groovy (and Java) implement a so called short-circuit logical operator. The result of the expression is returned as soon as it is known. Since by associativity, the expression is evaluated left to right, in the case P && Q, if P is false, it doesn't matter what the value of Q is, the result is false. Similarly in the case P || Q, if P is true, then the result is true, whatever the value of Q. This short-circuit effect has a marginal impact on the computation efficiency because if the result can be decided based on the value of P alone, then Q (which may be a complex expression) doesn't have to evaluated.

To illustrate this consider the example:

1

def a = 10
def b = 20
def c = 30
:
def d = (b < a) && (c == 40)

Since the sub expression b < a is false, then the test c == 40 does not have to execute.

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