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Declaration: Definitions vs Declarations, Definitions and Declarations (computer programming): Type declaration - User-defined type declaration, Variable declaration - Constant declaration, Class declaration - Object declaration, Constructor declaration - Destructor declaration, Struct declaration - Record declaration, Function declaration - Method declaration, Lambda declaration - Anonymous function declaration, Enumerator declaration, Pointer declaration, Generic declaration - Template declaration, Interface declaration - Protocol declaration - Trait declaration, Namespace declaration, Package declaration, Module declaration, Alias declaration, Import declaration - Export declaration, Macro declaration. Programming terms. (navbar_declaration)
In object-oriented programming, an interface or protocol type is a data type that acts as an abstraction of a class. It describes a set of method signatures, the implementations of which may be provided by multiple classes that are otherwise not necessarily related to each other. A class which provides the methods listed in an interface is said to implement the interface, or to adopt the protocol.
Interfaces are useful for encapsulation and reducing coupling. For example, in Java, the
Comparableinterface specifies the methodcompareTo. Thus, a sorting method only needs to take objects of types which implementComparableto sort them, without knowing about the inner nature of the class (except that two of these objects can be compared viacompareTo()).
In computer programming, a declaration is a syntactic language construct is the process to specify identifier properties for its initialization: it declares a word's (identifier's) meaning. Declarations are most commonly used for functions, variables, constants, and classes, but can also be used for other entities such as enumerations and type definitions. Beyond the name (the identifier itself) and the kind of entity (function, variable, etc.), declarations typically specify the data type (for variables and constants), or the type signature (for functions); types may also include dimensions, such as for arrays. A declaration is used to announce the existence of the entity to the compiler; this is important in those strongly typed languages that require functions, variables, and constants, and their types to be specified with a declaration before use, and is used in forward declaration. The term "declaration" is frequently contrasted with the term "definition", but meaning and usage varies significantly between languages; see below.
Declarations are particularly prominent in languages in the ALGOL tradition, including the BCPL family, most prominently C and C++, and also Pascal. Java uses the term "declaration", though Java does not require separate declarations and definitions.
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