JetBrains Academy: Runtime type checking

Who is who:

You are given a class hierarchy consisting of three classes. The base class is Employee. The first subclass is Developer, the second subclass is DataAnalyst.

Implement a method determineWhoIsWho. The method takes an array of employees. Each element belongs to one of the listed classes. The method should output the type (DEV, EMP or DA) of each element in a new line.

Use the provided template for your method.

public static void determineWhoIsWho(Employee[] employees) {
    for (Employee employee : employees) {
        if (employee.getClass() == Developer.class){
            System.out.println("DEV");
        } else if(employee.getClass() == DataAnalyst.class){
            System.out.println("DA");
        } else {
            System.out.println("EMP");
        }
    }
}

Counting 2D shapes:

Below is a part of a class hierarchy consisting of a lot of classes:

class Shape { }
class Shape2D extends Shape { }
class Shape3D extends Shape { }
class Circle extends Shape2D { }
 
// ...  classes which extends Shape2D
 
class Cube extends Shape3D { }
 
// ...  classes which extends Shape3D

Implement a method that takes an array of shapes and counts how many objects of classes that extend Shape2D the array contains. Do not count objects of Shape2D, only its subclasses.

public static int count2DShapes(Shape[] shapes) {
    int counter = 0;
    for (Shape shape : shapes){
        if (shape instanceof Shape2D){
            if (shape.getClass() != Shape2D.class){
                counter++;
            }
        }
    }
    return counter;
}

Sort out the classes:

You are given 4 classes — Shape, Polygon, Square, Circle.

Classes Polygon and Circle both extend the class Shape, the class Square extends the class Polygon.

You need to implement a method that takes Shape array and adds every element to one of the provided Lists based on their class.

public static void sortShapes(Shape[] array,
                              List<Shape> shapes,
                              List<Polygon> polygons,
                              List<Square> squares,
                              List<Circle> circles) {
    for (Shape shape : array){
        if (shape instanceof Square){
            squares.add((Square) shape);
        } else if (shape instanceof Polygon){
            polygons.add((Polygon) shape);
        } else if (shape instanceof Circle){
            circles.add((Circle) shape);
        } else if (shape instanceof Shape){
            shapes.add(shape);
        }
    }
}

Sum of the areas:

You are given the following classes:

class Shape {} 

class Square extends Shape { 
    private int side; 
    public int getSide() { 
        return side; 
    } 
    public void setSide(int side) { 
        this.side = side; 
    } 
}
 
class Rectangle extends Shape { 
    private int width, height; 
    public int getWidth() { 
        return width; 
    } 
    public void setWidth(int width) {
        this.width = width; 
    } 
    public int getHeight() { 
        return height; 
    } 
    public void setHeight(int height) { 
        this.height = height; 
    } 
}

Unfortunately, the author of this class hierarchy forgot to add the getArea() method to these classes. Now you need to implement a method that calculates the sum of areas of the Shape array. If some elements are instances of the class Shape, their area equals 0.

public static int sumOfAreas(Shape[] array) {
    int area = 0;
    for (Shape shape : array){
        if (Square.class.isInstance(shape)){
            area += ((Square)shape).getSide() * ((Square)shape).getSide();
        } else if (Rectangle.class.isInstance(shape)){
            area += ((Rectangle)shape).getWidth() * ((Rectangle)shape).getHeight();
        } else if (Shape.class.isInstance(shape)){
            area += 0;
        }
    }
    return area;
}

JetBrains Academy: Runtime type checking - Kamil-Jankowski/Learning-JAVA GitHub Wiki

JetBrains Academy: Runtime type checking

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