Interfaces can not extend a class or implement an Interface
. An interface can extend another Interface. A non-abstract class which is implementing an Interface needs to follow some rules. This class needs to provide the concrete implementation of all abstract method.
Can we use non-abstract method in interface?
Interface methods are by definition public and abstract, so
you cannot have non-abstract methods in your interface
.
Can only abstract classes implement interfaces?
In Java, an abstract class
can implement an interface
, and not provide implementations of all of the interface’s methods. It is the responsibility of the first concrete class that has that abstract class as an ancestor to implement all of the methods in the interface.
Can any class implement an 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. A class can inherit a base class and also implement one or more interfaces.
Do interfaces have to be abstract?
Yes,
Interfaces can only have abstract methods
. 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. Method bodies exist only for default methods and static methods.
Can an abstract class implement?
Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. … In addition, you can extend only one class, whether or not it is abstract, whereas
you can implement any number of interfaces
.
What is the difference between interface and 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.
How do we implement private interface?
- A) Using Inherits Keyword.
- B) Using Implements Keyword.
- C) Private interfaces can not be implemented.
- Explanation: Interfaces must always be declared as public so that they can be implemented or inherited.
Why do we need interface instead of 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.
When would you use an abstract class instead of an interface?
Abstract classes should be used
primarily for objects that are closely related
, whereas interfaces are best suited for providing a common functionality to unrelated classes. Interfaces are a good choice when we think that the API will not change for a while.
Can an interface have a constructor?
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 we declare constructor as abstract?
Yes,
an Abstract class always has a constructor
. If you do not define your own constructor, the compiler will give a default constructor to the Abstract class.
What happens if an abstract class implements an interface?
A curious thing happens in Java when you use an abstract class to implement an interface:
some of the interface’s methods can be completely missing
(i.e. neither an abstract declaration or an actual implementation is present), but the compiler does not complain.
Can an abstract class implement an interface PHP?
Key point of interfaces: Interfaces can include abstract methods and constants, but cannot contain concrete methods and variables. All the methods in the interface must be in the public visibility scope. A
class can implement more than one interface
, while it can inherit from only one abstract class.
How many interfaces can an abstract class implement?
| Parameters Interface Abstract class | Speed Slow Fast | Multiple Inheritances Implement several Interfaces Only one abstract class | Structure Abstract methods Abstract & concrete methods | When to use Future enhancement To avoid independence |
|---|
