Painless supports one dynamic type: def. The def type can represent any primitive or reference type. When you use the def type, it mimics the exact behavior of whatever type it represents at runtime. The default value for the def type is null.

Internally, if the def type represents a primitive type, it is converted to the corresponding reference type. It still behaves like the primitive type, however, including within the casting model. The def type can be assigned to different types during the course of script execution.

Using the def type can have a slight impact on performance. If performance is critical, it’s better to declare static types.

Examples:

def x = 1;               // Declare def variable x and set it to the
                         //   literal int 1
def l = new ArrayList(); // Declare def variable l and set it a newly
                         //   allocated ArrayList

Primitive types are allocated directly onto the stack according to the standard Java memory model.

Primitive types can behave as their corresponding (boxed) reference type. This means any piece of a reference type can be accessed or called through the primitive type. Operations performed in this manner convert the primitive type to its corresponding reference type at runtime and perform the field access or method call without needing to perform any other operations.

Painless supports the following primitive types.

Examples:

int i = 1;        // Declare variable i as an int and set it to the
                  //   literal 1
double d;         // Declare variable d as a double and set it to the
                  //   default value of 0.0
boolean b = true; // Declare variable b as a boolean and set it to true

Using methods from the corresponding reference type on a primitive type.

int i = 1;    // Declare variable i as an int and set it to the
              //   literal 1
i.toString(); // Invokes the Integer method toString on variable i

Reference types are similar to Java classes and can contain multiple pieces known as members. However, reference types do not support access modifiers. You allocate reference type instances on the heap using the new operator.

Reference types can have both static and non-static members:

The default value for a reference type is null, indicating that no memory has been allocated for it. When you assign null to a reference type, its previous value is discarded and garbage collected in accordance with the Java memory model as long as there are no other references to that value.

A reference type can contain:

Reference types support a Java-style inheritance model. Consider types A and B. Type A is considered to be a parent of B, and B a child of A, if B inherits (is able to access as its own) all of A’s fields and methods. Type B is considered a descendant of A if there exists a recursive parent-child relationship from B to A with none to many types in between. In this case, B inherits all of A’s fields and methods along with all of the fields and methods of the types in between. Type B is also considered to be a type A in both relationships.

For the complete list of Painless reference types and their supported methods, see the Painless API Reference.

For more information about working with reference types, see Accessing Fields and Calling Methods.

Examples:

ArrayList al = new ArrayList();  // Declare variable al as an ArrayList and
                                 //   set it to a newly allocated ArrayList
List l = new ArrayList();        // Declare variable l as a List and set
                                 //   it to a newly allocated ArrayList, which is
                                 //   allowed because ArrayList inherits from List
Map m;                           // Declare variable m as a Map and set it
                                 //   to the default value of null

Directly accessing static pieces of a reference type.

Integer.MAX_VALUE      // a static field access
Long.parseLong("123L") // a static function call

A String is a specialized reference type that is immutable and does not have to be explicitly allocated. You can directly assign to a String without first allocating it with the new keyword. (Strings can be allocated with the new keyword, but it’s not required.)

When assigning a value to a String, you must enclose the text in single or double quotes. Strings are allocated according to the standard Java Memory Model. The default value for a String is null.

Examples:

String r = "some text";             // Declare String r and set it to the
                                    //   String "some text"
String s = 'some text';             // Declare String s and set it to the
                                    //   String 'some text'
String t = new String("some text"); // Declare String t and set it to the
                                    //   String "some text"
String u;                           // Declare String u and set it to the
                                    //   default value null

The void type represents the concept of no type. In Painless, void declares that a function has no return value.

Arrays contain a series of elements of the same type that can be allocated simultaneously. Painless supports both single and multi-dimensional arrays for all types except void (including def).

You declare an array by specifying a type followed by a series of empty brackets, where each set of brackets represents a dimension. Declared arrays have a default value of null and are themselves a reference type.

To allocate an array, you use the new keyword followed by the type and a set of brackets for each dimension. You can explicitly define the size of each dimension by specifying an expression within the brackets, or initialize each dimension with the desired number of values. The allocated size of each dimension is its permanent size.

To initialize an array, specify the values you want to initialize each dimension with as a comma-separated list of expressions enclosed in braces. For example, new int[] {1, 2, 3} creates a one-dimensional int array with a size of 3 and the values 1, 2, and 3.

When you initialize an array, the order of the expressions is maintained. Each expression used as part of the initialization is converted to the array’s type. An error occurs if the types do not match.

Grammar:

declare_array: TYPE ('[' ']')+;

array_initialization: 'new' TYPE '[' ']' '{' expression (',' expression) '}'
                    | 'new' TYPE '[' ']' '{' '}';

Examples:

int[] x = new int[5];          // Declare int array x and assign it a newly
                               //   allocated int array with a size of 5
def[][] y = new def[5][5];     // Declare the 2-dimensional def array y and
                               //   assign it a newly allocated 2-dimensional
                               //   array where both dimensions have a size of 5
int[] x = new int[] {1, 2, 3}; // Declare int array x and set it to an int
                               //   array with values 1, 2, 3 and a size of 3
int i = 1;
long l = 2L;
float f = 3.0F;
double d = 4.0;
String s = "5";
def[] da = new def[] {i, l, f*d, s}; // Declare def array da and set it to
                                     // a def array with a size of 4 and the
                                     // values i, l, f*d, and s