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

Should an interface have a constructor?

Constructor in an interface

An Interface in Java doesn't have a constructor because all data members in interfaces are public static final by default, they are constants (assign the values at the time of declaration). There are no data members in an interface to initialize them through the constructor.

Can an interface contain a constructor Java?

Interfaces can contain instance methods, properties, events, indexers, or any combination of those four member types. Interfaces may contain static constructors, fields, constants, or operators.

Can an interface have a constructor C#?

On implementation of an interface, you must override all of its methods. Interfaces can contain properties and methods, but not fields/variables. Interface members are by default abstract and public. An interface cannot contain a constructor (as it cannot be used to create objects)

Can you construct an interface object?

No, you cannot instantiate an interface. Generally, it contains abstract methods (except default and static methods introduced in Java8), which are incomplete.

Constructor In Interface/Abstract Class... Allowed Or Not ???

Can we declare interface as final?

If you make an interface final, you cannot implement its methods which defies the very purpose of the interfaces. Therefore, you cannot make an interface final in Java.

Can interface be a superclass?

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

Can abstract class have a constructor?

Like any other classes in Java, abstract classes can have constructors even when they are only called from their concrete subclasses.

Can we write static method in interface?

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.

What happens when constructor is defined for an interface?

What happens when a constructor is defined for an interface? Explanation: Constructor is not provided by interface as objects cannot be instantiated.

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 declare interface as abstract?

The interface body can contain abstract methods, default methods, and static methods. An abstract method within an interface is followed by a semicolon, but no braces (an abstract method does not contain an implementation).

CAN interface have instance variables?

No interface cannot have instance variable.

CAN interface 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 private methods?

An interface can have private methods since Java 9 version. These methods are visible only inside the class/interface, so it's recommended to use private methods for confidential code. That's the reason behind the addition of private methods in interfaces.

Can abstract class and interface have constructor?

Yes, an Abstract Class can have a Constructor. You Can Overload as many Constructor as you want in an Abstract Class. These Contractors Can be used to Initialized the initial state of the Objects Extending the Abstract Class.

Can we override default method in interface?

A class can override a default interface method and call the original method by using super , keeping it nicely in line with calling a super method from an extended class. But there is one catch, you need to put the name of the interface before calling super this is necessary even if only one interface is added.

CAN interfaces contain nested types?

Yes, if we define a class inside the interface, the Java compiler creates a static nested class. Let's see how can we define a class within the interface: interface M{

CAN interface have non static variables?

No you cannot have non-static variables in an interface. By default, 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).

Can constructor be private?

Yes, we can declare a constructor as private. If we declare a constructor as private we are not able to create an object of a class. We can use this private constructor in the Singleton Design Pattern.

Can we create immutable class in Java?

In Java, when we create an object of an immutable class, we cannot change its value. For example, String is an immutable class. Hence, we cannot change the content of a string once created. Besides, we can also create our own custom immutable classes.

Can we make constructor final?

No, a constructor can't be made final. A final method cannot be overridden by any subclasses. As mentioned previously, the final modifier prevents a method from being modified in a subclass. The main intention of making a method final would be that the content of the method should not be changed by any outsider.

Can an interface have a subclass?

No. An interface defines how a class should look like (as a bare minimum). Whether you implement this in a base class or in the lowest subclass doesn't matter.

Can we inherit interface in Java?

An interface cannot implement another interface in Java. An interface in Java is essentially a special kind of class. Like classes, the interface contains methods and variables. Unlike classes, interfaces are always completely abstract.

CAN interfaces have methods?

Like a class, an interface can have methods and variables, but the methods declared in an interface are by default abstract (only method signature, no body). Interfaces specify what a class must do and not how.