There are four basic data types in UJML: boolean, int, string, and reference. The boolean and int data types are 'primitive' in the sense that they are stored and passed by value. The string is a 'complex' data type in that it is stored and passed as a pointer to an array of characters elsewhere in memory. The reference data type is also 'complex', consisting of a reference to an an instance of a UJML component elsewhere in memory. See Components.

Arrays of a single data type are supported. See Arrays. There is no support for compound data types (other than arrays).

Component instances may be stored as reference types, but may also be stored as interface types, which allow access to the methods and events exposed by an interface implemented by the component instance. See Components, Interfaces, Interface Types.

Arrays, Literals and Constants, State Variables, Variables, Scripting, Using Functions, Components