Groovy by feature - Making Java Groovy - page 402

Closure Arguments

If the last argument to a method is a closure, it can be placed after the parentheses.

The upto and downto methods take two arguments, so the parentheses are shown in the
former and a comma is used in the latter to indicate that both the number and the closure
are arguments to the method. The countDown variable is a list, which will be discussed
in section B.3 . The left-shift operator has been overloaded to append to the collection, and
its argument here is a parameterized string. Groovy has two types of strings, discussed in
the next section.

B.2.2. Strings and Groovy strings

In Java, single quotes delimit characters (a primitive) and double quotes surround instances
of java.lang.String . In Groovy, both single and double quotes are used for strings,
butthere'sadifference.Double-quotedstringsareusedforparameter replacement. They're
not instances of

java.lang.String ,

but rather instances of

groovy.lang.GString .

Here are a couple of examples to show how they're used:

def s = 'this is a string'
assert s.class == java.lang.String

def gs = "this might be a GString"
assert gs.class == java.lang.String
assert !(gs instanceof GString)

gs = "If I put in a placeholder, this really is a GString: ${1+1}"
assert gs instanceof GString

Single-quoted strings are always instances of java.lang.String . Double-quoted
strings may or may not be Groovy strings, depending on whether parameter replacement is
done or not.