- Why use an interface instead of a class?
- What is the interface of a class?
- When would you use an interface?
- Can an interface contain constants?
- Is WebElement an interface or a class?
- What are the similarities between interfaces and classes?
- Which is better abstract class or interface?
- When a class implements an interface it must?
- What happens when a class implements an interface?
- How do you define an interface?
- Can a class contain an interface?
- What is difference between interface and abstract class?
- Can abstract class have constructor?
- Can we declare an interface as final?
- Can we have method body in interface?
- Can an abstract class implement an interface?
- How do we declare an interface class?
- What are the similarities and differences between abstract classes and interfaces?
- What is Interface explain with example?
- Can we create object of interface?
- Should I always use interfaces?
Why use an interface instead of a class?
An interface defines common functionality across unrelated classes.
For example, all sorts of classes that look nothing like each other may have the need to safely get rid of the resources they use.
The IDisposable interface (the name for it in .
NET) defines a Dispose() method, which classes then implement..
What is the interface of a class?
Like a class, an interface defines methods. Unlike a class, an interface never implements methods; instead, classes that implement the interface implement the methods defined by the interface. A class can implement multiple interfaces.
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.
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.
Is WebElement an interface or a class?
Represents an HTML element. Generally, all interesting operations to do with interacting with a page will be performed through this interface.
What are the similarities between interfaces and classes?
Similarities between Interface and Abstract Class:-We can’t create object for both.All the abstract methods must be overridden by subclass.Don’t have default constructor.By using both we can go for dynamic polymorphism.Both can contain static and final variable.More items…•
Which is better abstract class or interface?
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.
When a class implements an interface it must?
When a class implements an interface, what must it do? It must declare a variable for each constant in the interface. You just studied 9 terms!
What happens when a class implements an interface?
When a class implements an interface, you can think of the class as signing a contract, agreeing to perform the specific behaviors of the interface. If a class does not perform all the behaviors of the interface, the class must declare itself as abstract. A class uses the implements keyword to implement an interface.
How do you define an interface?
An interface declaration can have two other components: the public access specifier and a list of superinterfaces. An interface can extend other interfaces just as a class can extend or subclass another class. However, while a class can only extend one other class, an interface can extend any number of interfaces.
Can a class contain an interface?
Yes, you can define a class inside an interface. In general, if the methods of the interface use this class and if we are not using it anywhere else we will declare a class within an interface.
What is difference between interface and abstract class?
Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. … Variables declared in a Java interface is by default final. An abstract class may contain non-final variables. Members of a Java interface are public by default.
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.
Can we declare an 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. Still if you try to do so, a compile time exception is generated saying “illegal combination of modifiers − interface and final”.
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.
Can an abstract class implement an interface?
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.
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.
What are the similarities and differences between abstract classes and interfaces?
Abstract class can be extended using extends keyword. We can achieve multiple inheritance using interface as we can implement multiple interfaces to any class. Abstract class doesn’t support multiple inheritance as we can not extend more than one class. Interface can not hold main method, static methods or constructor.
What is Interface explain with example?
Difference between Class and InterfaceClassInterfaceClass can contain concrete(with implementation) methodsThe interface cannot contain concrete(with implementation) methodsThe access specifiers used with classes are private, protected and public.In Interface only one specifier is used- Public.1 more row•Dec 3, 2020
Can we create object of interface?
No, you cannot instantiate an interface. Generally, it contains abstract methods (except default and static methods introduced in Java8), which are incomplete.
Should I always use interfaces?
No, every class should not have an interface. … You use an interface when you need to abstract what’s done from how it’s done, and you’re certain that the implementation can change. Have a look at the java. util Collections API for a good example.