Can we instantiate interface?

An interface can't be instantiated directly. Its members are implemented by any class or struct that implements the interface. A class or struct can implement multiple interfaces.

Can I instantiate interface in Java?

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.

Why can't we instantiate an interface?

You can't instantiate an interface or an abstract class because it would defy the object oriented model. Interfaces represent contracts - the promise that the implementer of an interface will be able to do all these things, fulfill the contract.

Can we instantiate an interface if yes how?

No, you cannot instantiate an interface. Generally, it contains abstract methods (except default and static methods introduced in Java8), which are incomplete. Still if you try to instantiate an interface, a compile time error will be generated saying “MyInterface is abstract; cannot be instantiated”.

Can we instantiate interface and abstract class?

No you can not instantiate an interface or abstract class. But you can instantiate an anonymous class that implements/extends the interface or abstract class without defining a class object.

How Method returns instance of Interface in Java?

Can we have constructor in interface?

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. From Java9 onwards interfaces allow private and private static methods.

CAN interface have non-abstract methods?

Interface methods are by definition public and abstract, so you cannot have non-abstract methods in your interface.

Can we instantiate interface C#?

Interface can not be directly instantiated. We can create an instance of a class that implements the interface, then assign that instance to a variable of the interface type.

CAN interface have instance variables?

No interface cannot have instance variable.

Can we create instance of interface C#?

Actually you cannot create an instance of an interface. You create an instance of some class, implementing the interface. Actually there can be dozens of classes, implementing one interface.

Can we override constructor?

Constructor looks like method but it is not. It does not have a return type and its name is same as the class name. But, a constructor cannot be overridden. If you try to write a super class's constructor in the sub class compiler treats it as a method and expects a return type and generates a compile time error.

Can we inherit abstract class?

An abstract class cannot be inherited by structures. It can contain constructors or destructors. It can implement functions with non-Abstract methods. It cannot support multiple inheritances.

What class Cannot be instantiated?

An abstract class cannot be instantiated. The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share.

Can we instantiate runnable interface?

You cannot instantiate an interface. Nor an abstract class.

Can interface be extended?

An interface can extend other interfaces, just as a class subclass or extend another class. However, whereas a class can extend only one other class, an interface can extend any number of interfaces. The interface declaration includes a comma-separated list of all the interfaces that it extends.

Can interface be a superclass?

An Interface is not a superclass because a class can only have one superclass but implement multiple Interfaces.

CAN interface have static methods?

Static methods in an interface since java8

Since Java8 you can have static methods in an interface (with body). You need to call them using the name of the interface, just like static methods of a class.

CAN interfaces have concrete methods?

Interfaces cannot have any concrete methods. If you need the ability to have abstract method definitions and concrete methods then you should use an abstract class.

CAN interface have final variable?

an interface can be empty, with no methods or variables in it. we can't use the final word in the interface definition, as it will result in a compiler error. all interface declarations should have the public or default access modifier; the abstract modifier will be added automatically by the compiler.

Can we call interface methods?

In order to call an interface method from a java program, the program must instantiate the interface implementation program. A method can then be called using the implementation object.

Why are interfaces better than classes?

A class can be instantiated i.e, objects of a class can be created. An Interface cannot be instantiated i.e, objects cannot be created. Classes does not support multiple inheritance. Interface supports multiple inheritance.

Can functional interface have 2 abstract methods?

A functional interface is an interface that contains only one abstract method. They can have only one functionality to exhibit. From Java 8 onwards, lambda expressions can be used to represent the instance of a functional interface.

Can we write method body in interface?

There can be only abstract methods in the Java interface, not the method body. It is used to achieve abstraction and multiple inheritance in Java. In other words, you can say that interfaces can have abstract methods and variables. It cannot have a method body.

Can you implement multiple interfaces?

A class can implement more than one interface at a time. A class can extend only one class, but implement many interfaces. An interface can extend another interface, in a similar way as a class can extend another class.

Can abstract method be instantiated?

Abstract classes cannot be instantiated, but they can be subclassed. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, then the subclass must also be declared abstract .