Groovy literal StringBuilder/StringBuffer

String.leftShift() creates a StringBuffer.

AFAICS, you cannot create a StringBuilder via groovy syntax sugar. You can only create a StringBuilder explicitly. No operator overload on String or GString creates a StringBuilder that you can explicitly use. Java String concatenation might create a StringBuilder, but that instance wouldn't be usable in your code.

At the time of writing this answer:

• Another answer said to use <<=. <<= is merely a java compound assignment that uses <<. In particular, there is no method for overloading <<=.
• The accepted answer said to use ''<<'' //4 single quotes, not double quotes. Double quotes work fine, at least on modern groovy.

The following code shows that we always get a StringBuffer, not a StringBuilder, for the result of various combinations of << vs <<= and "" vs '':

def ls = ''<<''
println ls.class
def lse = ''
lse <<=''
println lse.class

ls = ""<<''
println ls.class
lse = ""
lse <<=''
println lse.class

ls = ''<<""
println ls.class
lse = ''
lse <<=""
println lse.class

ls = ""<<""
println ls.class
lse = ""
lse <<=""
println lse.class

prints:

class java.lang.StringBuffer
class java.lang.StringBuffer
class java.lang.StringBuffer
class java.lang.StringBuffer
class java.lang.StringBuffer
class java.lang.StringBuffer
class java.lang.StringBuffer
class java.lang.StringBuffer

I've just played with StringBuilder / StringBuffer in Groovy.

Some examples below:

// << operator example
def year = StringBuilder.newInstance()
year << 2
year << "0"
year << '1' << 4
assert year.toString() == "2014"

// You can use with operator
def month = StringBuilder.newInstance()
month.with {
    append "0"
    append '5'
}
assert month.toString() == "05"

// or just append String like in Java or you can leave parenthesis
def day = StringBuilder.newInstance()
day.append "1"
day.append('1')
assert day.toString() == '11'

// It's nice to know, that we can use StringBuilder directly in GString
def date = "$year-${month}-$day"
assert date == "2014-05-11"

Note: Use StringBuilder when it is used only by one thread. StringBuilder provides an API compatible with StringBuffer. StringBuffer is synchronized, StringBuilder is not. Check this link for more info.

To create a StringBuffer:

text = 'Hello '

To append:

text <<= 'World!'

And this might help some more.

To get a StringBuffer in a single step, you could use

def sb = 'Hello'<<''

or even:

def sb = ''<<'' //4 single quotes, not double quotes

for an initially empty one.

I think (but I could be wrong) the reason for using a StringBuffer rather than a StringBuilder is to maintain compatibility with Java 1.4.