What does extend class mean?

Asked By: Magen Guio | Last Updated: 30th May, 2020
Category: technology and computing programming languages
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Extending a Class. You can extend a class to provide more specialized behavior. A class that extends another class inherits all the methods and properties of the extended class. This means that the behavior of a particular method is different based on the object you're calling it on.

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Also question is, what does it mean to extend a class?

Definition and Usage The extends keyword extends a class (indicates that a class is inherited from another class). In Java, it is possible to inherit attributes and methods from one class to another. We group the "inheritance concept" into two categories: subclass (child) - the class that inherits from another class.

Subsequently, question is, can a class extend itself? A class cannot extend itself since it IS itself, The definition of subclass is that it extends another class and inherits the state and behaviors from that class. so it is not a subclass. Inner classes are allowed to extend the outer class because those are two different classes.

In this way, when should you extend a class?

You extend a class when you want the new class to have all the same features of the original, and something more. The child class may then either add new functionalities, or override some funcionalities of the parent class.

What is the use of extends keyword?

It specifies the super class in a class declaration using extends keyword. It is a keyword that indicates the parent class that a subclass is inheriting from and may not be used as identifiers i.e. you cannot declare a variable or class with this name in your Java program.

33 Related Question Answers Found

Does every class extend object?

Every class in Java is directly or indirectly derived from the Object class. If a Class does not extend any other class then it is direct child class of Object and if extends other class then it is an indirectly derived. Hence Object class acts as a root of inheritance hierarchy in any Java Program.

Can you extend more than one class in Java?

No, Java cannot extend multiple classes. To use this feature create “Interface” then implement it. In Java you can inherit one and only one class at a time. Java does not supports extend multiple classes or what we call Multiple inheritance.

What is difference between inheritance and interface?

They are inheritance, polymorphism, abstraction and encapsulation. Inheritance and interfaces are related to OOP. The key difference between inheritance and interface is that inheritance is to derive new classes from existing classes and an interface is to implement abstract classes and multiple inheritance.

What is the difference between implements and extends?

Difference: implements means you are using the elements of a Java Interface in your class. extends means that you are creating a subclass of the base class you are extending. You can only extend one class in your child class, but you can implement as many interfaces as you would like.

How do you extend an abstract class?


Abstract classes:
  1. abstract classes can't be instantiated, only subclassed.
  2. other classes extend abstract classes.
  3. can have both abstract and concrete methods.
  4. similar to interfaces, but (1) can implement methods, (2) fields can have various access modifiers, and (3) subclasses can only extend one abstract class.

What is meant by multiple inheritance?

Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inherit characteristics and features from more than one parent object or parent class.

What is an interface?

In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hardware, peripheral devices, humans, and combinations of these.

Why do we use inheritance?

The major purpose of inheritance is to make a specific section of your project's code reusable with the possibility of adding or removing certain features later. A child class can inherit or override certain methods from the parent class it inherited its methods from without changing the parent class itself.

Why Multiple inheritance is dangerous?

The danger with multiple inheritance is complexity. Since you might affect multiple modules in your app from the same parent classes, it's not that easy to reason about code changes. Any mistake could cause a chain reaction of bugs. This is where multiple inheritance can become productive.

Is inheritance a good thing?


But that aside, inheritance is invaluable for accomplishing many good things. Polymorphism (specifically sub-type polymorphism) is a very powerful tool and single and double dispatch are key for patterns such as Visitor pattern. Interface inheritance is key to designing to interfaces, not implementations.

What is Polymorphism in Java?

Polymorphism in Java is a concept by which we can perform a single action in different ways. We can perform polymorphism in java by method overloading and method overriding. If you overload a static method in Java, it is the example of compile time polymorphism. Here, we will focus on runtime polymorphism in java.

Can an abstract class extend a class?

Abstract classes can extend other at most one abstract or concrete class and implement several interfaces. Any class that does not implement all the abstract methods of it's super class has to be an abstract class itself.

Why we use implements keyword in Java?

The extends keyword is mainly used to extend a class i.e. to create a subclass in Java, while implements keyword is used to implement an interface in Java. The extends keyword can also be used by an interface for extending another interface.

Why is inheritance important in OOP?

One of the most important concepts in object-oriented programming is that of inheritance. Inheritance allows us to define a class in terms of another class, which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and fast implementation time.

How do you extend a class in C#?


Binding Extension Methods at Compile Time
You can use extension methods to extend a class or interface, but not to override them. An extension method with the same name and signature as an interface or class method will never be called.

How do you stop an inheritance?

To prevent inheritance, use the keyword "final" when creating the class. The designers of the String class realized that it was not a candidate for inheritance and have prevented it from being extended.

Can a constructor be inherited?

Constructors are not members of classes and only members are inherited. You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a constructor of one of it's superclasses.