Strings
Strings are a sequence of characters.
There are multiple ways to define a string and each does something different.
Warning
Strings in Java function differently that in Groovy! Read here to see a direct comparison.
Single-Quoted String
The most simple way is by using ''. This creates a String, and nothing else. In most cases this is what you want.
Double-Quoted String
A more advanced way is by using "". This creates a GString instead of a String, which allows you to use variables inside the literal via the dollar sign $.
You can read more about GStrings on the official documentation
Tip
Because GString can have unexpected results when containing a dollar sign $, you should use single quotes '' unless you explicitly desire the features of a GString.
Slashy String
The last way is by using \\. This is perfect for regex, because you don't need to escape any \.
Examples
def s = 'hello' // String
def s2 = "hello" // can use either '' or ""
assert s == s2 // both strings are equal
def num = 7
def numberOfDays = 'There are ' + num + ' days in a week' // using a variable inside the string with concatenation
def numberOfDays2 = "There are $num days in a week" // using a variable inside the string with $
Waiting Idly
Nullpinter