http://docs.groovy-lang.org/latest/html/groovy-jdk/java/lang/Character.html
http://docs.groovy-lang.org/latest/html/groovy-jdk/java/lang/CharSequence.html
http://docs.groovy-lang.org/latest/html/groovy-jdk/java/lang/String.html

def s = 'this is a string'
assert s.getClass() == java.lang.String

def s = "this is a string"
assert s.getClass() == java.lang.String // compiler optimized out because there are no any interpolation

def s = "this is a string ${1 + 1}"
assert s.instanceOf GString == org.codehaus.groovy.runtime.GStringImpl // GString in the groovy docs API
assert s.getClass() == org.codehaus.groovy.runtime.GStringImpl // GString in the groovy docs API


CharSequence i-face

def s = 'this is a string'
s + ' and more'
s - 'is' // look at CharSequence.minus - removes a first occurence
s * 3
s[0]
s[-1]    // last letter
s[-2]    // but last last letter
s[0..3]  // groovy range
s[0..3,5..7,8,10..-1]

Regular multiline strings
def picard = '''\
line 1
line 2
'''

Interpolated (Groovy) multiline strings:
def picard = """...
...
${...}
...
"""

Slashy strings:
def zip = /\d{5}(-\d{4})?/
    java.lang.String
    we don't have to backslash the backslashes
def zip = ~/\d{5}(-\d{4})?/
    java.util.regex.Pattern

assert '....' =~ zip
assert '....' ==~ zip

string.split()
    split string by spaces as delimiters

String [] strs = "a b c".split()
List strsList = "a b c".split() // auto-convert

String.toURL()
URL.getText()

'http://oreilly.com'.goURL().text  // return URL page content :)

String(CharSequence).eachLine(Closure c)
URL.eachLine(Closure c)
List readLines()

padding:
padLeft(numChars, padding)
    toBinaryString(str).padLeft(4, '0')