Question: Can An Interface Have A Class?

Can an interface extend 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..

Can an interface contain constants?

It’s possible to place widely used constants in an interface. If a class implements such an interface, then the class can refer to those constants without a qualifying class name. This is only a minor advantage.

What is difference between abstract class and interface?

Classes can implement multiple interfaces, but only one abstract class. Abstract classes can contain non-abstract methods. They can both have methods, variables, and neither one can be instantiated. All variables declared in an interface are final, while an abstract class may contain non-final variables.

Can we declare static method inside interface?

You can’t define static methods in an interface because static methods belongs to a class not to an instance of class, and interfaces are not Classes. Read more here. In this case what you have is two classes with 2 distinct static methods called methodX().

Why use an interface instead of a class?

Having interfaces separate from classes allows for clear separation between, well, the interface of an object and its implementation. Without them you would have no standard way to indicate that some class should not contain implementation details at all.

Can an interface extend a class?

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.

Can you have fields in an interface?

An interface in Java is a specification of method prototypes. … All the members (methods and fields) of an interface are public. All the methods in an interface are public and abstract (except static and default). All the fields of an interface are public, static and, final by default.

When would you use an interface?

Use interface when you want to exactly implement all the abstract methods to the class implementaing the interface and no default body to a method can be provided. It is considered good style to store a reference to a HashSet or TreeSet in a variable of type Set.

How do we declare an interface class?

An interface is declared by using the interface keyword. It provides total abstraction; means all the methods in an interface are declared with the empty body, and all the fields are public, static and final by default. A class that implements an interface must implement all the methods declared in the interface.

Can a class contain an interface?

Yes, you can define an interface inside a class and it is known as a nested interface. You can’t access a nested interface directly; you need to access (implement) the nested interface using the inner class or by using the name of the class holding this nested interface.

Can abstract class have constructor?

Yes! Abstract classes can have constructors! Yes, when we define a class to be an Abstract Class it cannot be instantiated but that does not mean an Abstract class cannot have a constructor. Each abstract class must have a concrete subclass which will implement the abstract methods of that abstract class.

What are the advantages of interface?

1) through interfaces we can implement multiple inheritance in java. 2) Interfaces function to break up the complex designs and clear the dependencies between objects. 3) Interfaces makes your application loosely coupled.

Should I use interface or abstract class?

The short answer: An abstract class allows you to create functionality that subclasses can implement or override. An interface only allows you to define functionality, not implement it. And whereas a class can extend only one abstract class, it can take advantage of multiple interfaces.

Can an interface have a class or another interface as it’s members?

Related Articles. We can declare interfaces as member of a class or another interface. Such an interface is called as member interface or nested interface. Interfaces (or classes) can have only public and default access specifiers when declared outside any other class (Refer this for details).

Can we have method body in interface?

All methods of an Interface do not contain implementation (method bodies) as of all versions below Java 8. Starting with Java 8, default and static methods may have implementation in the interface definition. … Interfaces cannot be instantiated, but rather are implemented.