Control flowedit

Painless supports all of Java’s control flow statements except the switch statement.

Painless also supports the for in syntax from Groovy:

for (item : list) {
  ...
}

Functionsedit

You can declare functions at the beginning of a Painless script, for example:

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

Lambda expressionsedit

Lambda expressions and method references work the same as in Java.

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);

You can make method references to functions within the script with this, for example list.sort(this::mycompare).

Patternsedit

Regular expression constants are directly supported. To ensure fast performance, this is the only mechanism for creating patterns. Regular expressions are always constants and compiled efficiently a single time.

Pattern p = /[aeiou]/

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 of the flags from Java’s Pattern class using these characters:

Dereferencesedit

Like lots of languages, Painless uses . to reference fields and call methods:

String foo = 'foo';
TypeWithGetterOrPublicField bar = new TypeWithGetterOrPublicField()
return foo.length() + bar.x

Like Groovy, Painless uses ?. to perform null-safe references, with the result being null if the left hand side is null:

String foo = null;
return foo?.length()  // Returns null

Unlike Groovy, Painless doesn’t support writing to null values with this operator:

TypeWithSetterOrPublicField foo = null;
foo?.x = 'bar'  // Compile error