Interface can instantiated

For more information about explicit implementation, see Explicit Interface Implementation and Interface Properties. 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. That class may be implicitly converted to the derived interface or any of its base interfaces.

A class might include an interface multiple times through base classes that it inherits or through interfaces that other interfaces inherit. However, the class can provide an implementation of an interface only one time and only if the class declares the interface as part of the definition of the class class ClassName : InterfaceName. If the interface is inherited because you inherited a base class that implements the interface, the base class provides the implementation of the members of the interface.

However, the derived class can reimplement any virtual interface members instead of using the inherited implementation. When interfaces declare a default implementation of a method, any class implementing that interface inherits that implementation You need to cast the class instance to the interface type to access the default implementation on the Interface member.

A base class can also implement interface members by using virtual members. In that case, a derived class can change the interface behavior by overriding the virtual members. For more information about virtual members, see Polymorphism. Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. Skip to main content. This browser is no longer supported.

Download Microsoft Edge More info. Contents Exit focus mode. Make, this. How do I know when to implement that interface or when to create this type of object from it? You can never instantiate an interface in java. You can, however, refer to an object that implements an interface by the type of the interface. So what is happening is that getSharedPreferences returns an object that implements that interface. The type of the returned object is not important. What is important is that it implements all the methods for that interface, so it can be used as an SharedPreferences.

SharedPreferences is a reference, but you are not creating a SharedPreferences object. Rather, you are creating an object that is of that type; namely, an implementation of that type. You do not create a class that implements this interface, because somebody has already created one for you.

You use this class via its interface, without even knowing the class name. That's what interfaces are for. SharedPreferences is an interface implemented in Context. What you see here is an example of abstracting towards an interface: by defining your pref variable as an interface you allow for easier code changes your current class is now loosely coupled with the Context class instead of putting a direct link towards it. The object returned by Context.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? We can't create object of interfaces because of the reason that : Interface is basically a complete abstract class. So if we don't have any implementation of a method then that means if we create object of that interface and call that method it compile nothing as there is no code to compile. That means you can take a reference variable of an interface but you can not create an instance of an interface just like an abstract class.

Even in Java 8 : you cannot instantiate interfaces. You can never instantiate an interface in java. All fields in interface are public static final , i. It is generally recommended to avoid such interfaces , but sometimes you can find an interface that has no methods and is used only to contain list of constant values.

Interfaces cannot be instantiated , but rather are implemented. A class that implements an interface must implement all of the non-default methods described in the interface , or be an abstract class. Interfaces in Object Oriented Programming Languages. For example, say we have a car class and a scooter class and a truck class.

Why do we need interface? It also ensures that you follow programming to interface than implementation pattern, which eventually adds lot of flexibility in your system. How do you use an interface? Java uses Interface to implement multiple inheritance. A Java class can implement multiple Java Interfaces. All methods in an interface are implicitly public and abstract. To use an interface in your class, append the keyword "implements" after your class name followed by the interface name.

What is an interface? An interface is a reference type in Java. It is similar to class. It is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface.