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An interface in the Java programming language is an abstract type that is used to declare a behavior that classes must implement. They are similar to protocols.Interfaces are declared using the interface keyword, and may only contain method signature and constant declarations (variable declarations that are declared to be both static and final).
A class defines an implementation of an interface, and instantiating the class results in an object that exposes the implementation via the interface. [3] In the terms of type theory, a class is an implementation—a concrete data structure and collection of subroutines—while a type is an interface .
Java has a set of predefined annotation types, but it is allowed to define new ones. An annotation type declaration is a special type of an interface declaration. They are declared in the same way as the interfaces, except the interface keyword is preceded by the @ sign.
Static import is a feature introduced in the Java programming language that allows members (fields and methods) which have been scoped within their container class as public static, to be used in Java code without specifying the class in which the field has been defined.
static is a reserved word in many programming languages to modify a declaration. The effect of the keyword varies depending on the details of the specific programming language, most commonly used to modify the lifetime (as a static variable) and visibility (depending on linkage), or to specify a class member instead of an instance member in classes.
An instance of the interface is syntactically no more useful than the interface name itself (since it has no methods). Unless a developer checks any implemented interfaces when adding a constant to a class, or does so but makes a typo in the name of the added constant, the value of a constant can be silently changed. Consider Example 2 below.
For example, if there were a Product class it might have a static method to compute the average price of all products. A static method can be invoked even if no instances of the class exist yet. Static methods are called "static" because they are resolved at compile time based on the class they are called on and not dynamically as in the case ...
In computer programming, a declaration is a language construct specifying identifier properties: it declares a word's (identifier's) meaning. [1] 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. [1]