Abstract classes in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an abstract class named Vehicle.

Java

public [1] class Vehicle {}

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Afinal

Bprivate

Cstatic

Dabstract

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' instead of 'abstract' which prevents inheritance.

Using 'static' which is not valid for top-level classes.

Using 'private' which is an access modifier, not for abstract classes.

The keyword abstract is used to declare an abstract class in Java.

2fill in blank

medium

Complete the code to declare an abstract method named startEngine in the Vehicle class.

Java

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

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Afinal

Babstract

Cstatic

Dprivate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' which means the method cannot be overridden.

Using 'static' which is not allowed for abstract methods.

Using 'private' which prevents subclass access.

The abstract keyword is used to declare a method without a body inside an abstract class.

3fill in blank

hard

Fix the error in the code by completing the class declaration to make it abstract.

Java

public [1] {
    public abstract void startEngine();
}

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Aabstract class Car

Bclass Car

Cfinal class Car

Dstatic class Car

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving out 'abstract' causes a compilation error.

Using 'final' prevents subclassing which is needed for abstract methods.

Using 'static' is invalid for top-level classes.

The class must be declared abstract if it contains abstract methods.

4fill in blank

hard

Fill both blanks to complete the subclass Car that extends the abstract class Vehicle and implements the startEngine method.

Java

public class Car [1] Vehicle {
    @Override
    public void startEngine() [2]
}

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Aextends

Bimplements

C()

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'implements' which is for interfaces, not classes.

Using parentheses instead of braces for method body.

The subclass uses extends to inherit from the abstract class. The method body is enclosed in {}.

5fill in blank

hard

Fill all three blanks to complete the abstract class Shape with an abstract method area, and a concrete method displayArea that prints the area.

Java

public abstract class Shape {
    public abstract double [1]();

    public void [2]() {
        System.out.println("Area: " + [3]());
    }
}

Drag options to blanks, or click blank then click option'

Aarea

BdisplayArea

DprintArea

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the method calls causing errors.

Not matching method names exactly.

The abstract method is named area. The concrete method is displayArea which calls area() to get the value.