Painless Syntaxedit

Warning

The Painless scripting language is new and is still marked as experimental. The syntax or API may be changed in the future in non-backwards compatible ways if required.

Variable typesedit

Painless supports all of Java’s types, including array types, but adds some additional built-in types.

Defedit

The dynamic type def serves as a placeholder for any other type. It adopts the behavior of whatever runtime type it represents.

Stringedit

String constants can be declared with single quotes, to avoid escaping horrors with JSON:

def mystring = 'foo';

Listedit

Lists can be created explicitly (e.g. new ArrayList()) or initialized similar to Groovy:

def list = [1,2,3];

Lists can also be accessed similar to arrays: they support subscript and .length:

def list = [1,2,3];
return list[0]

Mapedit

Maps can be created explicitly (e.g. new HashMap()) or initialized similar to Groovy:

def person = ['name': 'Joe', 'age': 63];

Map keys can also be accessed as properties.

def person = ['name': 'Joe', 'age': 63];
person.retired = true;
return person.name

Map keys can also be accessed via subscript (for keys containing special characters):

return map['something-absurd!']

Patternedit

Regular expression constants are directly supported:

Pattern p = /[aeiou]/

Patterns can only be created via this mechanism. This ensures fast performance, regular expressions are always constants and compiled efficiently a single time.

Pattern flagsedit

You can define flags on patterns in Painless by adding characters after the trailing / like /foo/i or /foo \w #comment/iUx. Painless exposes all the flags from Java’s Pattern class using these characters:

CharacterJava ConstantExample

c

CANON_EQ

'å' ==~ /å/c (open in hex editor to see)

i

CASE_INSENSITIVE

'A' ==~ /a/i

l

LITERAL

'[a]' ==~ /[a]/l

m

MULTILINE

'a\nb\nc' =~ /^b$/m

s

DOTALL (aka single line)

'a\nb\nc' =~ /.b./s

U

UNICODE_CHARACTER_CLASS

'Ɛ' ==~ /\\w/U

u

UNICODE_CASE

'Ɛ' ==~ /ɛ/iu

x

COMMENTS (aka extended)

'a' ==~ /a #comment/x

Operatorsedit

All of Java’s operators are supported with the same precedence, promotion, and semantics.

There are only a few minor differences and add-ons:

  • == behaves as Java’s for numeric types, but for non-numeric types acts as Object.equals()
  • === and !== support exact reference comparison (e.g. x === y)
  • =~ true if a portion of the text matches a pattern (e.g. x =~ /b/)
  • ==~ true if the entire text matches a pattern (e.g. x ==~ /[Bb]ob/)

Control flowedit

Java’s control flow statements are supported, with the exception of the switch statement.

In addition to Java’s enhanced for loop, the for in syntax from groovy can also be used:

for (item : list) {
  ...
}

Functionsedit

Functions can be declared at the beginning of the script, for example:

boolean isNegative(def x) { x < 0 }
...
if (isNegative(someVar)) {
  ...
}

Lambda expressionsedit

Lambda expressions and method references work the same as Java’s.

list.removeIf(item -> item == 2);
list.removeIf((int item) -> item == 2);
list.removeIf((int item) -> { item == 2 });
list.sort((x, y) -> x - y);
list.sort(Integer::compare);

Method references to functions within the script can be accomplished using this, e.g. list.sort(this::mycompare).