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<\/p>\n<\/p>\n
A concrete class is one that provides implementations for all its methods, leaving no room for unimplemented methods. Such a class can either extend an abstract class or implement an interface, as long as it fulfills all the required method implementations. Being a complete class, it is capable of being instantiated.<\/p>\n
Put simply, any class that is not abstract is considered a concrete class.<\/p>\n
In Java, a concrete class is a class that can be instantiated, and it must meet the following necessary conditions:<\/p>\n
Let’s consider an example of a concrete class in Java called Rectangle.<\/p>\n
public class Rectangle {\n private double width;\n private double height;\n\n public Rectangle(double width, double height) {\n this.width = width;\n this.height = height;\n }\n\n public double getArea() {\n return width * height;\n }\n\n public double getPerimeter() {\n return 2 * (width + height);\n }\n\n public void printDetails() {\n System.out.println(\"Rectangle - Width: \" + width + \", Height: \" + height);\n }\n}<\/code><\/pre>\nExplanation<\/strong>
\nIn the example above, we have a class named Rectangle, which represents a simple rectangle shape. This class is a concrete class because it satisfies the necessary conditions for being concrete:<\/p>\n1. It is not declared as abstract:<\/strong> There is no abstract keyword in the class declaration, making it a concrete class.
\n2. It provides implementations for all its methods:<\/strong> The class has three methods: getArea(), getPerimeter(), and printDetails(). Each of these methods has a complete implementation, leaving no methods without an implementation.
\n3. It does not extend an abstract class without implementing its abstract methods:<\/strong> In this case, the Rectangle class does not extend any other class, so there’s no abstract class to implement.
\n4. It does not fail to implement methods from implemented interfaces:<\/strong> The Rectangle class does not implement any interfaces, so this condition does not apply.<\/p>\nThe Rectangle class has two private instance variables width and height, representing the dimensions of the rectangle. The constructor initializes these variables with the provided values. The getArea() method calculates the area of the rectangle, the getPerimeter() method calculates its perimeter, and the printDetails() method prints the width and height of the rectangle to the console.<\/p>\n
Since the Rectangle class meets all the necessary conditions for a concrete class, you can create instances of it and use its methods without any issues. For example:<\/p>\n
public class Main {\n public static void main(String[] args) {\n Rectangle rectangle = new Rectangle(5.0, 3.0);\n System.out.println(\"Area: \" + rectangle.getArea());\n System.out.println(\"Perimeter: \" + rectangle.getPerimeter());\n rectangle.printDetails();\n }\n}<\/code><\/pre>\nOutput:<\/strong><\/p>\nArea: 15.0\nPerimeter: 16.0\nRectangle - Width: 5.0, Height: 3.0<\/code><\/pre>\n\t\t\t\t\t\t