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Types

A type is a classification of data used to define the properties of a value. These properties specify what data a value represents and the rules for how a value is evaluated during an operation. Each type belongs to one of the following categories: primitive, reference, or dynamic.

A primitive type represents basic data built natively into the JVM and is allocated to non-heap memory. Declare a primitive type variable or access a primitive type member field (from a reference type instance), and assign it a primitive type value for evaluation during later operations. The default value for a newly-declared primitive type variable is listed as part of the definitions below. A primitive type value is copied during an assignment or as an argument for a method/function call.

A primitive type has a corresponding reference type (also known as a boxed type). Use the field access operator or method call operator on a primitive type value to force evaluation as its corresponding reference type value.

The following primitive types are available. The corresponding reference type is listed in parentheses. For example, Byte is the reference type for the byte primitive type:

Examples

  • Primitive types used in declaration, declaration and assignment.

    int i = 1;
double d;
boolean b = true;
    1. declare int i; store int 1 to i
    2. declare double d; store default double 0.0 to d
    3. declare boolean b; store boolean true to b

  • Method call on a primitive type using the corresponding reference type.

    int i = 1;
i.toString();
    1. declare int i; store int 1 to i
    2. load from i → int 1; box int 1 → Integer 1 reference; call toString on Integer 1 reference → String '1'

A reference type is a named construct (object), potentially representing multiple pieces of data (member fields) and logic to manipulate that data (member methods), defined as part of the application programming interface (API) for scripts.

A reference type instance is a single set of data for one reference type object allocated to the heap. Use the new instance operator to allocate a reference type instance. Use a reference type instance to load from, store to, and manipulate complex data.

A reference type value refers to a reference type instance, and multiple reference type values may refer to the same reference type instance. A change to a reference type instance will affect all reference type values referring to that specific instance.

Declare a reference type variable or access a reference type member field (from a reference type instance), and assign it a reference type value for evaluation during later operations. The default value for a newly-declared reference type variable is null. A reference type value is shallow-copied during an assignment or as an argument for a method/function call. Assign null to a reference type variable to indicate the reference type value refers to no reference type instance. The JVM will garbage collect a reference type instance when it is no longer referred to by any reference type values. Pass null as an argument to a method/function call to indicate the argument refers to no reference type instance.

A reference type object defines zero-to-many of each of the following:

static member field
A static member field is a named and typed piece of data. Each reference type object contains one set of data representative of its static member fields. Use the field access operator in correspondence with the reference type object name to access a static member field for loading and storing to a specific reference type object. No reference type instance allocation is necessary to use a static member field.
non-static member field
A non-static member field is a named and typed piece of data. Each reference type instance contains one set of data representative of its reference type object’s non-static member fields. Use the field access operator for loading and storing to a non-static member field of a specific reference type instance. An allocated reference type instance is required to use a non-static member field.
static member method
A static member method is a function called on a reference type object. Use the method call operator in correspondence with the reference type object name to call a static member method. No reference type instance allocation is necessary to use a static member method.
non-static member method
A non-static member method is a function called on a reference type instance. A non-static member method called on a reference type instance can load from and store to non-static member fields of that specific reference type instance. Use the method call operator in correspondence with a specific reference type instance to call a non-static member method. An allocated reference type instance is required to use a non-static member method.
constructor
A constructor is a special type of function used to allocate a reference type instance defined by a specific reference type object. Use the new instance operator to allocate a reference type instance.

A reference type object follows a basic 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 non-static members. 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 non-static members along with all of the non-static members of the types in between. Type B is also considered to be a type A in both relationships.

Examples

  • Reference types evaluated in several different operations.

    List l = new ArrayList();
l.add(1);
int i = l.get(0) + 2;
    1. declare List l; allocate ArrayList instance → ArrayList reference; implicit cast ArrayList reference to List reference → List reference; store List reference to l
    2. load from l → List reference; implicit cast int 1 to def → def call add on List reference with arguments (def)
    3. declare int i; load from l → List reference; call get on List reference with arguments (int 0) → def; implicit cast def to int 1 → int 1; add int 1 and int 2 → int 3; store int 3 to i

  • Sharing a reference type instance.

    List l0 = new ArrayList();
List l1 = l0;
l0.add(1);
l1.add(2);
int i = l1.get(0) + l0.get(1);
    1. declare List l0; allocate ArrayList instance → ArrayList reference; implicit cast ArrayList reference to List reference → List reference; store List reference to l0
    2. declare List l1; load from l0 → List reference; store List reference to l1 (note l0 and l1 refer to the same instance known as a shallow-copy)
    3. load from l0 → List reference; implicit cast int 1 to def → def call add on List reference with arguments (def)
    4. load from l1 → List reference; implicit cast int 2 to def → def call add on List reference with arguments (def)
    5. declare int i; load from l0 → List reference; call get on List reference with arguments (int 0) → def @0; implicit cast def @0 to int 1 → int 1; load from l1 → List reference; call get on List reference with arguments (int 1) → def @1; implicit cast def @1 to int 2 → int 2; add int 1 and int 2 → int 3; store int 3 to i;

  • Using the static members of a reference type.

    int i = Integer.MAX_VALUE;
long l = Long.parseLong("123L");
    1. declare int i; load from MAX_VALUE on Integer → int 2147483647; store int 2147483647 to i
    2. declare long l; call parseLong on Long with arguments (long 123) → long 123; store long 123 to l

A dynamic type value can represent the value of any primitive type or reference type using a single type name def. A def type value mimics the behavior of whatever value it represents at run-time and will always represent the child-most descendant type value of any type value when evaluated during operations.

Declare a def type variable or access a def type member field (from a reference type instance), and assign it any type of value for evaluation during later operations. The default value for a newly-declared def type variable is null. A def type variable or method/function parameter can change the type it represents during the compilation and evaluation of a script.

Using the def type can have a slight impact on performance. Use only primitive types and reference types directly when performance is critical.

Errors

  • If a def type value represents an inappropriate type for evaluation of an operation at run-time.

Examples

  • General uses of the def type.

    def dp = 1;
def dr = new ArrayList();
dr = dp;
    1. declare def dp; implicit cast int 1 to def → def; store def to dp
    2. declare def dr; allocate ArrayList instance → ArrayList reference; implicit cast ArrayList reference to def → def; store def to dr
    3. load from dp → def; store def to dr; (note the switch in the type dr represents from ArrayList to int)

  • A def type value representing the child-most descendant of a value.

    Object l = new ArrayList();
def d = l;
d.ensureCapacity(10);
    1. declare Object l; allocate ArrayList instance → ArrayList reference; implicit cast ArrayList reference to Object reference → Object reference; store Object reference to l
    2. declare def d; load from l → Object reference; implicit cast Object reference to def → def; store def to d;
    3. load from d → def; implicit cast def to ArrayList reference → ArrayList reference; call ensureCapacity on ArrayList reference with arguments (int 10); (note def was implicit cast to ArrayList reference since ArrayListis the child-most descendant type value that thedef` type value represents)

The String type is a specialized reference type that does not require explicit allocation. Use a string literal to directly evaluate a String type value. While not required, the new instance operator can allocate String type instances.

Examples

  • General use of the String type.

    String r = "some text";
String s = 'some text';
String t = new String("some text");
String u;
    1. declare String r; store String "some text" to r
    2. declare String s; store String 'some text' to s
    3. declare String t; allocate String instance with arguments (String "some text") → String "some text"; store String "some text" to t
    4. declare String u; store default null to u

The void type represents the concept of a lack of type. Use the void type to indicate a function returns no value.

Examples

  • Use of the void type in a function.

    void addToList(List l, def d) {
    l.add(d);
}

An array type is a specialized reference type where an array type instance contains a series of values allocated to the heap. Each value in an array type instance is defined as an element. All elements in an array type instance are of the same type (element type) specified as part of declaration. Each element is assigned an index within the range [0, length) where length is the total number of elements allocated for an array type instance.

Use the new array operator or the array initialization operator to allocate an array type instance. Declare an array type variable or access an array type member field (from a reference type instance), and assign it an array type value for evaluation during later operations. The default value for a newly-declared array type variable is null. An array type value is shallow-copied during an assignment or as an argument for a method/function call. Assign null to an array type variable to indicate the array type value refers to no array type instance. The JVM will garbage collect an array type instance when it is no longer referred to by any array type values. Pass null as an argument to a method/function call to indicate the argument refers to no array type instance.

Use the array length operator to retrieve the length of an array type value as an int type value. Use the array access operator to load from and store to an individual element within an array type instance.

When an array type instance is allocated with multiple dimensions using the range [2, d] where d >= 2, each element within each dimension in the range [1, d-1] is also an array type. The element type of each dimension, n, is an array type with the number of dimensions equal to d-n. For example, consider int[][][] with 3 dimensions. Each element in the 3rd dimension, d-3, is the primitive type int. Each element in the 2nd dimension, d-2, is the array type int[]. And each element in the 1st dimension, d-1 is the array type int[][].

Examples

  • General use of single-dimensional arrays.

    int[] x;
float[] y = new float[10];
def z = new float[5];
y[9] = 1.0F;
z[0] = y[9];
    1. declare int[] x; store default null to x
    2. declare float[] y; allocate 1-d float array instance with length [10] → 1-d float array reference; store 1-d float array reference to y
    3. declare def z; allocate 1-d float array instance with length [5] → 1-d float array reference; implicit cast 1-d float array reference to def → def; store def to z
    4. load from y → 1-d float array reference; store float 1.0 to index [9] of 1-d float array reference
    5. load from y → 1-d float array reference @0; load from index [9] of 1-d float array reference @0 → float 1.0; load from z → def; implicit cast def to 1-d float array reference @1 → 1-d float array reference @1; store float 1.0 to index [0] of 1-d float array reference @1

  • General use of a multi-dimensional array.

    int[][][] ia3 = new int[2][3][4];
ia3[1][2][3] = 99;
int i = ia3[1][2][3];
    1. declare int[][][] ia; allocate 3-d int array instance with length [2, 3, 4] → 3-d int array reference; store 3-d int array reference to ia3
    2. load from ia3 → 3-d int array reference; store int 99 to index [1, 2, 3] of 3-d int array reference
    3. declare int i; load from ia3 → 3-d int array reference; load from index [1, 2, 3] of 3-d int array reference → int 99; store int 99 to i