Kotlin OOP Program: Shape base class and Polymorphic subclasses

Kotlin OOP Program: Exercise-1 with Solution

Write a Kotlin object-oriented program that creates a base class Shape and derives subclasses Circle, Rectangle, and Triangle. Implement appropriate methods in each class and demonstrate polymorphism.

Sample Solution:

Kotlin Code:

abstract class Shape {
    abstract fun area(): Double
    abstract fun perimeter(): Double
}

class Circle(private val radius: Double) : Shape() {
    override fun area(): Double {
        return Math.PI * radius * radius
    }

    override fun perimeter(): Double {
        return 2 * Math.PI * radius
    }
}

class Rectangle(private val width: Double, private val height: Double) : Shape() {
    override fun area(): Double {
        return width * height
    }

    override fun perimeter(): Double {
        return 2 * (width + height)
    }
}

class Triangle(private val side1: Double, private val side2: Double, private val side3: Double) : Shape() {
    override fun area(): Double {
        val semiPerimeter = perimeter() / 2
        return Math.sqrt(semiPerimeter * (semiPerimeter - side1) * (semiPerimeter - side2) * (semiPerimeter - side3))
    }

    override fun perimeter(): Double {
        return side1 + side2 + side3
    }
}

fun main() {
    val circle = Circle(4.5)
    val rectangle = Rectangle(7.0, 11.0)
    val triangle = Triangle(4.0, 5.0, 6.0)

    val shapes = listOf(circle, rectangle, triangle)

    for (shape in shapes) {
        println("Area: ${shape.area()}")
        println("Perimeter: ${shape.perimeter()}")
        println()
    }
}

Sample Output:

Area: 63.61725123519331
Perimeter: 28.274333882308138

Area: 77.0
Perimeter: 36.0

Area: 9.921567416492215
Perimeter: 15.0

Explanation:

In the above exercise -

• The "Shape" class is declared as an abstract class with two abstract methods: "area()" and "perimeter()". The Circle, Rectangle, and Triangle classes inherit from the "Shape" class and provide their own implementations of these methods.
• In the "main()" function, instances of Circle, Rectangle, and Triangle are created and stored in a list. Using a loop, the program demonstrates polymorphism by calling the area() and perimeter() methods on each shape object. This dynamically invokes the appropriate implementation based on the actual object type.
• The output of the program will display the area and perimeter of each shape.

Kotlin Editor:

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