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Heritage

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Release: 2024-09-10 06:48:06
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  • Inheritance is one of the three basic principles of object-oriented programming.

  • Allows the creation of hierarchical classifications.

  • With inheritance, you can create a general class that defines characteristics common to a set of related items.

  • This general class can be inherited by other more specific classes, which add exclusive characteristics.

  • In Java jargon, the inherited class is called a superclass.

  • The class that inherits is called a subclass.

  • The subclass is a specialized version of the superclass.

  • The subclass inherits all variables and methods from the superclass and adds its own unique elements.

Basic aspects of inheritance

  • Java supports inheritance, allowing one class to incorporate another in its declaration.

  • This is done with the extends keyword.

  • The subclass adds functionality (extends) to the superclass.

  • An example of this is the creation of a superclass called TwoDShape, which stores the width and height of a two-dimensional object.

  • A subclass called Triangle is created to extend TwoDShape.

  • The extends keyword is used to create the subclass.

Heritage

Heritage

  • TwoDShape defines attributes of a generic two-dimensional shape, such as square, rectangle, triangle, etc.

  • The Triangle class is a subclass of TwoDShape and creates a specific type: the triangle.

  • Triangle inherits everything from TwoDShape and adds the style field, the area() method, and the showStyle() method.

  • style stores the style of the triangle, which can be any description such as "full", "contour", or "isosceles".

  • The area() method calculates and returns the area of the triangle.

  • The showStyle() method displays the style of the triangle.

  • Triangle can access the width and height members of TwoDShape, both in area() and directly in the t1 and t2 objects.

  • TwoDShape, despite being a superclass of Triangle, is an independent class and can be used separately.

TwoDShape shape = new TwoDShape();
shape.width = 10;
shape.height = 20;
shape.showDim();

  • An object of the TwoDShape class does not know about or access any subclass of TwoDShape.

Heritage

  • Declaration of a class that inherits a superclass:

class subclass-name extends superclass-name {
// class body
}

  • In Java, you can only specify a single superclass for any subclass you create.

  • Java does not support multiple inheritance (inheritance from multiple superclasses in the same subclass), unlike C++.

  • It is possible to create an inheritance hierarchy where a subclass becomes the superclass of another subclass.

  • No class can be a superclass of itself.

  • An advantage of inheritance is that a superclass can define attributes common to multiple objects, allowing the creation of numerous specific subclasses.

  • Each subclass can define its own specific classification based on the superclass.

  • An example of this is creating a subclass of TwoDShape to encapsulate rectangles.

Heritage

  • The Rectangle class is a subclass of TwoDShape.

  • Adds the isSquare() method, which determines whether the rectangle is a square (when the width is equal to the height).

  • Also adds the area() method, which calculates the area of the rectangle.

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source:dev.to
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