Why polymorphism is needed in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a method that all shapes can use.

Java

public abstract class Shape {
    public abstract void [1]();
}

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Adraw

Bpaint

Cshow

Ddisplay

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a method name that is not descriptive of the action.

Using a method name that is not consistent with common naming.

The method draw is commonly used to represent drawing a shape. Declaring it abstract means all subclasses must provide their own version.

2fill in blank

medium

Complete the code to override the draw method in Circle class.

Java

public class Circle extends Shape {
    @Override
    public void [1]() {
        System.out.println("Drawing a circle");
    }
}

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Apaint

Bdraw

Cshow

Ddisplay

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name than the abstract method.

Forgetting to use @Override annotation.

The draw method overrides the abstract method in Shape to provide specific behavior for Circle.

3fill in blank

hard

Fix the error in the code to call the draw method polymorphically.

Java

Shape shape = new Circle();
shape.[1]();

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Adraw

Bdisplay

Cshow

Dpaint

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a method not declared in Shape.

Trying to call a method that does not exist.

Calling draw() on the Shape reference will invoke the Circle's overridden method due to polymorphism.

4fill in blank

hard

Fill both blanks to create a list of shapes and call draw on each.

Java

List<[1]> shapes = new ArrayList<>();
shapes.add(new Circle());
for ([2] shape : shapes) {
    shape.draw();
}

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AShape

BCircle

CObject

DDrawable

Attempts:

3 left

💡 Hint

Common Mistakes

Using subclass type for the list which limits polymorphism.

Using unrelated types that do not have draw method.

Using the base class Shape for the list and loop variable allows polymorphic calls to draw() on any subclass.

5fill in blank

hard

Fill all four blanks to demonstrate polymorphism with different shapes.

Java

Shape [1] = new Circle();
Shape [2] = new Rectangle();
[3].draw();
[4].draw();

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AcircleShape

BrectShape

Cshape1

Dshape2

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same variable name for both shapes.

Calling draw on a variable not declared.

Using different variable names for shapes allows calling draw() polymorphically on each specific shape instance.