Why inheritance is used in Java - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why do we use inheritance in Java?

Inheritance allows one class to take properties and methods from another class. Why is this useful?

A To reuse code and create a relationship between classes

B To make the program run faster by skipping methods

C To hide all methods from other classes

D To prevent any changes in the parent class

💡 Hint

Think about how sharing common features can save time and effort.

Inheritance helps reuse code by letting a child class use the code of a parent class. This creates a clear relationship and reduces repetition.

❓ Predict Output

intermediate

Output of inheritance example

What will be the output of this Java code?

Java

class Animal {
    void sound() {
        System.out.println("Animal makes a sound");
    }
}
class Dog extends Animal {
    void sound() {
        System.out.println("Dog barks");
    }
}
public class Test {
    public static void main(String[] args) {
        Animal a = new Dog();
        a.sound();
    }
}

A Runtime error

B Animal makes a sound

C Compilation error

D Dog barks

💡 Hint

Remember that the method called depends on the actual object type, not the reference type.

The object is of type Dog, so Dog's sound() method runs, printing 'Dog barks'. This is called method overriding.

🔧 Debug

advanced

Identify the inheritance error

What error will this code produce?

Java

class Parent {
    void show() {
        System.out.println("Parent class");
    }
}
class Child extends Parent {
    void show(int x) {
        System.out.println("Child class: " + x);
    }
}
public class Test {
    public static void main(String[] args) {
        Child c = new Child();
        c.show();
    }
}

A Runtime error: NullPointerException

B Output: Parent class

C Output: Child class: 0

D Compilation error: method show() not found in Child

💡 Hint

Check if the Child class inherits the show() method without parameters.

Child class inherits show() from Parent. The show(int x) is an overload, not override. Calling c.show() calls Parent's show().

📝 Syntax

advanced

Correct inheritance syntax

Which option shows the correct way to inherit a class in Java?

A class Child inherits Parent {}

B class Child implements Parent {}

C class Child extends Parent {}

D class Child uses Parent {}

💡 Hint

Java uses a specific keyword to inherit from a class.

The keyword extends is used to inherit from a class in Java.

🚀 Application

expert

Number of methods accessible via inheritance

Given these classes, how many methods can an object of class C call?

class A {
  void m1() {}
  void m2() {}
}
class B extends A {
  void m3() {}
}
class C extends B {
  void m4() {}
}

A 4

B 3

C 2

D 5

💡 Hint

Count all methods from class C and its parents.

Class C inherits m1() and m2() from A, m3() from B, and has m4() itself. Total 4 methods.