Question: Can An Interface Be Final?

Can an interface be private?

A top-level interface cannot be private.

It can only have public or package access.

A nested interface can be private whenever it and its subclasses, if any, are an implementation detail of its top-level class.

For example, the nested interface CLibrary below is used as an implementation detail of the top-level class..

Can variables be declared in an interface?

In Java , interface doesn’t allow you to declare any instance variables. Using a variable declared in an interface as an instance variable will return a compile time error. You can declare a constant variable, using static final which is different from an instance variable.

Can an interface have a constructor?

No, you cannot have a constructor within an interface in Java. You can have only public, static, final variables and, public, abstract, methods as of Java7. From Java8 onwards interfaces allow default methods and static methods.

Can we extend an interface?

An interface can extend another interface in the same way that a class can extend another class. The extends keyword is used to extend an interface, and the child interface inherits the methods of the parent interface. The following Sports interface is extended by Hockey and Football interfaces.

How do you access interface variables?

Interface Variables must be Final An interface does not have instance variables. The members of an interface are always declared as static and final, that the variable cannot be modified by the methods in the class. Such variables will be inherited by the class that implements the interface.

Can you inherit an interface?

Interfaces can inherit from one or more interfaces. The derived interface inherits the members from its base interfaces. A class that implements a derived interface must implement all members in the derived interface, including all members of the derived interface’s base interfaces.

Can I inherit one interface from another interface if yes how if no why?

An interface can extend any number of interfaces but one interface cannot implement another interface, because if any interface is implemented then its methods must be defined and interface never has the definition of any method.

Can interface inherit abstract class?

An interface can inherit multiple interfaces but cannot inherit a class. An abstract class can inherit a class and multiple interfaces. … An interface can have only public abstract methods. An abstract class has protected and public abstract methods.

Can an interface extend an abstract class?

Remember, a Java class can only have 1 superclass, but it can implement multiple interfaces. Thus, if a class already has a different superclass, it can implement an interface, but it cannot extend another abstract class. Therefore interfaces are a more flexible mechanism for exposing a common interface.

What can an interface contain?

In the Java programming language, an interface is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static methods, and nested types.

CAN interface have non final variables?

Final Variables: Variables declared in a Java interface are by default final. An abstract class may contain non-final variables. Type of variables: Abstract class can have final, non-final, static and non-static variables. Interface has only static and final variables.