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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).
As multiple inheritance is not allowed in Java, interfaces are used to circumvent it. An interface can be defined within another interface. long The long keyword is used to declare a variable that can hold a 64-bit signed two's complement integer. [5] [6] This keyword is also used to declare that a method returns a value of the primitive type ...
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, in Java, the Comparable interface specifies a method compareTo() which implementing classes must implement. This means that a sorting method, for example, can sort a collection of any objects of types which implement the Comparable interface, without having to know anything about the inner nature of the class (except that two of ...
The choice of a variable name should be mnemonic — that is, designed to indicate to the casual observer the intent of its use. One-character variable names should be avoided except for temporary "throwaway" variables. Common names for temporary variables are i, j, k, m, and n for integers; c, d, and e for characters. int i;
According to Java Language Specification: [5] A type variable is an unqualified identifier. Type variables are introduced by generic class declarations, generic interface declarations, generic method declarations, and by generic constructor declarations. A class is generic if it declares one or more type variables. [6]
For example, the Java language does not allow client code that accesses the private data of a class to compile. [12] In the C++ language, private methods are visible, but not accessible in the interface; however, they may be made invisible by explicitly declaring fully abstract classes that represent the interfaces of the class. [13]
In .NET, they are called "custom attributes", in Java they are called "annotations". Despite the different name, they are conceptually the same thing. They can be defined on classes, member variables, methods, and method parameters and may be accessed using reflection. In Python, the term "marker interface" is common in Zope and Plone.