String concatenation with Groovy
What is the best (idiomatic) way to concatenate Strings in Groovy?
Option 1:
calculateAccountNumber(bank, branch, checkDigit, account) {
bank + branch + checkDigit + account
}
Option 2:
calculateAccountNumber(bank, branch, checkDigit, account) {
"$bank$branch$checkDigit$account"
}
I've founded an interesting point about this topic in the old Groovy website: Things you can do but better leave undone.
As in Java, you can concatenate Strings with the "+" symbol. But Java only needs that one of the two items of a "+" expression to be a String, no matter if it's in the first place or in the last one. Java will use the toString() method in the non-String object of your "+" expression. But in Groovy, you just should be safe the first item of your "+" expression implements the plus() method in the right way, because Groovy will search and use it. In Groovy GDK, only the Number and String/StringBuffer/Character classes have the plus() method implemented to concatenate strings. To avoid surprises, always use GStrings.
I always go for the second method (using the GString template), though when there are more than a couple of parameters like you have, I tend to wrap them in ${X} as I find it makes it more readable.
Running some benchmarks (using Nagai Masato's excellent GBench module) on these methods also shows templating is faster than the other methods:
@Grab( 'com.googlecode.gbench:gbench:0.3.0-groovy-2.0' )
import gbench.*
def (foo,bar,baz) = [ 'foo', 'bar', 'baz' ]
new BenchmarkBuilder().run( measureCpuTime:false ) {
// Just add the strings
'String adder' {
foo + bar + baz
}
// Templating
'GString template' {
"$foo$bar$baz"
}
// I find this more readable
'Readable GString template' {
"${foo}${bar}${baz}"
}
// StringBuilder
'StringBuilder' {
new StringBuilder().append( foo )
.append( bar )
.append( baz )
.toString()
}
'StringBuffer' {
new StringBuffer().append( foo )
.append( bar )
.append( baz )
.toString()
}
}.prettyPrint()
That gives me the following output on my machine:
Environment
===========
* Groovy: 2.0.0
* JVM: Java HotSpot(TM) 64-Bit Server VM (20.6-b01-415, Apple Inc.)
* JRE: 1.6.0_31
* Total Memory: 81.0625 MB
* Maximum Memory: 123.9375 MB
* OS: Mac OS X (10.6.8, x86_64)
Options
=======
* Warm Up: Auto
* CPU Time Measurement: Off
String adder 539
GString template 245
Readable GString template 244
StringBuilder 318
StringBuffer 370
So with readability and speed in it's favour, I'd recommend templating ;-)
NB: If you add toString() to the end of the GString methods to make the output type the same as the other metrics, and make it a fairer test, StringBuilder and StringBuffer beat the GString methods for speed. However as GString can be used in place of String for most things (you just need to exercise caution with Map keys and SQL statements), it can mostly be left without this final conversion
Adding these tests (as it has been asked in the comments)
'GString template toString' {
"$foo$bar$baz".toString()
}
'Readable GString template toString' {
"${foo}${bar}${baz}".toString()
}
Now we get the results:
String adder 514
GString template 267
Readable GString template 269
GString template toString 478
Readable GString template toString 480
StringBuilder 321
StringBuffer 369
So as you can see (as I said), it is slower than StringBuilder or StringBuffer, but still a bit faster than adding Strings...
But still lots more readable.
Edit after comment by ruralcoder below
Updated to latest gbench, larger strings for concatenation and a test with a StringBuilder initialised to a good size:
@Grab( 'org.gperfutils:gbench:0.4.2-groovy-2.1' )
def (foo,bar,baz) = [ 'foo' * 50, 'bar' * 50, 'baz' * 50 ]
benchmark {
// Just add the strings
'String adder' {
foo + bar + baz
}
// Templating
'GString template' {
"$foo$bar$baz"
}
// I find this more readable
'Readable GString template' {
"${foo}${bar}${baz}"
}
'GString template toString' {
"$foo$bar$baz".toString()
}
'Readable GString template toString' {
"${foo}${bar}${baz}".toString()
}
// StringBuilder
'StringBuilder' {
new StringBuilder().append( foo )
.append( bar )
.append( baz )
.toString()
}
'StringBuffer' {
new StringBuffer().append( foo )
.append( bar )
.append( baz )
.toString()
}
'StringBuffer with Allocation' {
new StringBuffer( 512 ).append( foo )
.append( bar )
.append( baz )
.toString()
}
}.prettyPrint()
gives
Environment
===========
* Groovy: 2.1.6
* JVM: Java HotSpot(TM) 64-Bit Server VM (23.21-b01, Oracle Corporation)
* JRE: 1.7.0_21
* Total Memory: 467.375 MB
* Maximum Memory: 1077.375 MB
* OS: Mac OS X (10.8.4, x86_64)
Options
=======
* Warm Up: Auto (- 60 sec)
* CPU Time Measurement: On
user system cpu real
String adder 630 0 630 647
GString template 29 0 29 31
Readable GString template 32 0 32 33
GString template toString 429 0 429 443
Readable GString template toString 428 1 429 441
StringBuilder 383 1 384 396
StringBuffer 395 1 396 409
StringBuffer with Allocation 277 0 277 286
def my_string = "some string"
println "here: " + my_string
Not quite sure why the answer above needs to go into benchmarks, string buffers, tests, etc.
Reproducing tim_yates answer on current hardware and adding leftShift() and concat() method to check the finding:
'String leftShift' {
foo << bar << baz
}
'String concat' {
foo.concat(bar)
.concat(baz)
.toString()
}
The outcome shows concat() to be the faster solution for a pure String, but if you can handle GString somewhere else, GString template is still ahead, while honorable mention should go to leftShift() (bitwise operator) and StringBuffer() with initial allocation:
Environment
===========
* Groovy: 2.4.8
* JVM: OpenJDK 64-Bit Server VM (25.191-b12, Oracle Corporation)
* JRE: 1.8.0_191
* Total Memory: 238 MB
* Maximum Memory: 3504 MB
* OS: Linux (4.19.13-300.fc29.x86_64, amd64)
Options
=======
* Warm Up: Auto (- 60 sec)
* CPU Time Measurement: On
user system cpu real
String adder 453 7 460 469
String leftShift 287 2 289 295
String concat 169 1 170 173
GString template 24 0 24 24
Readable GString template 32 0 32 32
GString template toString 400 0 400 406
Readable GString template toString 412 0 412 419
StringBuilder 325 3 328 334
StringBuffer 390 1 391 398
StringBuffer with Allocation 259 1 260 265
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.toString()appended to the two GString tests. My run shows that they then perform almost the same asString adder. My guess is that the test you've run doesn't actually handle the concatenation, so it's just creating a GString object and storing the references.StringBuilderis still the fastest, hands down, if you need aStringat some point.GString"as-is", at some point it has to be converted into a trueString, (even just to print it out), so the true timing is the last set. In the end the legibility ofGStringtemplates beatsStringBuilderwhen the timing is this close, so it's moot. :-)