Interface Nesting in Java Programming
In Java, interfaces can be declared within a class or another interface, commonly known as member interfaces or nested interfaces. Unlike standalone interfaces, these can have multiple access specifications: public, protected, package- private (default), or private.
When an interface is positioned within another, it becomes automatically public and static. However, top-level interfaces are only accessible with a public or package-private (default) specification. A nested interface can be exemplified as follows:
To implement a nested interface, it should be referred to as . The same applies to a nested interface inside a class:
A simple example demonstrates the access specification of a nested interface:
```javainterface Test {} // Package-private by default
// Alternatively, public, protected, or private access can be assigned to nested interfacespublic interface Test { ... }protected interface Test { ... }private interface Test { ... }```
An interface can also be declared within another interface. Since interfaces declared inside other interfaces are automatically public and static, the example below will result in a compilation error if an attempt is made to set it as private or protected:
Nested interfaces provide versatile applications in Java. They can help structure code, limit the scope of an interface, serve as callbacks, and establish contracts for different classes to follow. As a deep dive into the topic, continue to the next article on Marker Interfaces in Java.
A nested interface in Java, such as within another interface or class, is automatically public and static, making it accessible with the syntax. For example, when an interface is declared within another interface like , it's public by default and can't be assigned private or protected access. This characteristic of nested interfaces offers versatile applications, allowing for code structuring, limited interface scope, callback usage, and enforcing class contracts.
