Inheritance Interview Questions

Inheritance Interview Questions Of Java: In Java programming, Inheritance is a fundamental concept that expresses an “is-a” relationship between classes. This allows for reusing code and behaviors from parent classes by promoting a more organized and modular code structure. By default, all classes in Java inherit from the Object class.

Understanding inheritance is vital for Java developers, especially when facing interview questions. Below, we explore common interview questions related to inheritance in Java, providing concise answers to enhance your comprehension.

Common inheritance interview questions focus on the advantages of inheritance, such as code reuse and modeling real-world relationships. Other inheritance interview questions cover the inheritance hierarchy, inheritance relationships, superclasses, subclasses, and method overriding.

Additional inheritance programming and coding questions test the ability to implement inheritance in Java through creating superclass and subclass objects, calling inherited methods, and leveraging polymorphism. Inheritance supports critical Java OOP principles like encapsulation and abstraction.

As we proceed, we’ll address specific inheritance interview questions in Java, covering theoretical concepts and practical coding scenarios. Let’s look into the nuances of inheritance, ensuring you’re well-prepared for any interview question.

Java Inheritance Interview Questions

• What is the purpose of the ‘this’ keyword in Java?
• Explain the concept of Inheritance.
• Which class in Java is the superclass of every other class?
• Why Java does not support multiple inheritance?
• In OOPS, what is meant by composition?
• How aggregation and composition are different concepts?
• Why there are no pointers in Java?
• If there are no Java pointers, why do we get NullPointerException?
• What is the purpose of the ‘super’ keyword in Java?
• Is it possible to use this() and super() in the same constructor?
• What is the meaning of object cloning in Java?

What is inheritance in Java?
Ans: Acquiring features from existing entities is known as “inheritance.” The existing entity is called a super or parent class, and the new entity acquiring the features of an existing entity is called a sub-class or child class. The process of inheriting the properties and behaviors from one object to another is called Java. Creating a new class from an existing class using an IS-A relationship is known as “inheritance.”

How do you implement inheritance practically in Java?
Ans: There are two keywords in Java to implement is-a relationship

• Extends
• Implements.

What is the purpose of inheritance?
Ans: Inheritance offers reusable code, making Rapid Application Development (RAD) possible.

What are the generalized and specialized classes in Java?
Ans: The top-level or superclasses are known as “generalized classes.” They contain common data and behavior.
The low-level or sub-level classes are known as “specialized classes”. It contains more specific data.
Ex:

class Person
{
	int name;
	int age;
}
Class Student extends Person
{
	int rollNo;
	int marks;
}
class Employee extends Person
{
	int empId;
	float empSal;
}

In this class hierarchy, the Person is a generalized class, and Student and Employee are the specialized classes.

What are the types of inheritance?
Ans: The following are the types of inheritances:

• Single inheritance: If a class has only one parent class, that is known as “single inheritance”.
• Multiple inheritances

The following are two special cases of single inheritance supported by Java: Hierarchical Inheritance and Multi-level inheritance.

• Hierarchical inheritance: If a class has more than one sub-class, that form of single inheritance is especially known as “hierarchical inheritance”.
• Multi-level inheritance:
• Multiple Inheritance: Multiple inheritances are the mechanism of inheriting the features of more than one base class into a single class. Java does not support multiple inheritances, but they can be achieved using interfaces and implementing more than one interface in a class.

What is the purpose of the ‘super’ keyword in Java?
Ans: The following are the major uses of the super keyword they are:

• If your method overrides one of its super class’s methods, you can invoke the overridden method through the use of the keyword super.
• Using a super keyword, we can explicitly call the immediate superclass constructor from the subclass constructor.
• From sub-class, to access instance variables of superclass where a subclass also has a variable with the same name.

What are the differences between ‘this’ and ‘super’ keywords?
Ans: A call can be made to another constructor of the same class using’ this’ from within one constructor. Using the ‘super’ keyword, the superclass constructor is called from the sub-class constructor.

What are the rules to be followed while overriding a method?

Ans: The following are the rules to be followed while overriding a method:

• The overriding method has the same name, number, type of parameters, and return type as the method it overrides.
• For the child method, accessibility should not be reduced to that of the parent class method; equal or higher is ok.
• In the child method exception specification, extra checked exception classes should not be listed more than that of the parent class method; equal is ok, or less is ok.

What is the base class of all classes?
Ans: The java.lang. An object is the base class of all classes.

Does Java support multiple inheritances?
Ans: Java doesn’t support multiple inheritances.

How do you define a constant variable in Java?
Ans: The variable should be declared as static and final. So, only one copy of the variable exists for all class instances, and the value can’t be changed. static final int PI = 2.14; is an example for constant.

What is the purpose of declaring a variable as ‘final’?
Ans: A final variable’s value can’t be changed. The ‘final’ variables should be initialized before using them.

What is the impact of declaring a method as final?
Ans: A method declared as final cannot be overridden, and a subclass cannot have the same method signature with a different implementation.

I don’t want my class to be inherited by any other class. What should I do?
Ans: You should declare your class final. However, you can’t define it as final if it is abstract. No other class can extend a class declared final.

Can you give a few examples of final classes defined in Java API?
Ans: java.lang.String, java.lang.Math is the ‘final’ class.

How is the final different from finally and finalize()?
Ans: The ‘final’ is a modifier that can be applied to a class method or variable. The ‘final’ class can’t be inherited, the final method can’t be overridden, and the final variable can’t be changed. The ‘finally’ is an exception handling code section that gets executed whether an exception is raised or not by the try block code segment. The ‘finalize()’ is a method of the Object class that will be executed by the JVM just before garbage collecting objects to give a final chance for resource-releasing activity.

Does a class inherit the constructors of its superclass?
Ans: A class does not inherit constructors from any of its superclasses.

What is Overriding?
Ans: When a class defines a method using the same name, return type, and arguments as a method in its superclass, the method in the class overrides the method in the superclass. When the method is invoked for an object of the class, the new definition of the method is called, not the method definition from the superclass. Methods may be overridden to be more public, not more private.

How is this() and super() used with constructors?
Ans: The ‘this()’ method invokes a constructor of the same class. Meanwhile, the ’super()’ invokes a superclass constructor.

What modifiers are allowed for methods in an Interface?
Ans: Only public and abstract modifiers are allowed for methods in interfaces.

What are some alternatives to inheritance?
Ans: Delegation is an alternative to inheritance.  Delegation means including an instance of another class as an instance variable and forwarding messages to the instance. It is often safer than inheritance because it forces you to think about each message you forward. After all, the instance is of a known class rather than a new one, and because it doesn’t force you to accept all the superclass methods, you can provide only the methods that make sense. On the other hand, it makes you write more code, and it is harder to reuse (because it is not a subclass).

Does a class inherit the constructors of its superclass?
Ans: A class does not inherit constructors from any of its superclasses.

What restrictions are placed on method overloading?
Ans: Two methods may not have the same name and argument list but different return types.

What is method overloading & method overriding?
Ans: Method overloading occurs when a method in a class has the same method name but different arguments. Method overriding occurs when a method in a class has the same method name and the same arguments.

What is the difference between overloading & overriding?
Ans:

• In overloading, there is a relationship between methods available in the same class, whereas in overriding, there is a relationship between a superclass method and a subclass method.
• Overloading does not block inheritance from the superclass, whereas overriding blocks inheritance from the superclass.
• In overloading, separate methods share the same name, whereas in overriding, the subclass method replaces the superclass.
• Overloading must have different method signatures, whereas overriding must have the same signature.

What is meant by Inheritance, and what are its advantages?
Ans: Inheritance is inheriting all the features from a class. Its advantages are the reusability of code and accessibility of variables and methods of the superclass by subclasses.

What is the difference between the superclass and the subclass?
Ans: A superclass is an inherited class, whereas a subclass is a class that does the inheriting.

What modifiers may be used with top-level class?
Ans: The public, abstract, and final can be used for top-level classes.

If you find any mistakes in the above interview questions or want to share the missed questions, you can comment in the comment section.

Conclusion

Mastering Java inheritance is essential for any developer and automation tester, and being well-prepared for interview questions on this topic is paramount. We’ve covered a range of inheritance interview questions in Java, encompassing theoretical understanding, practical coding scenarios, and the advantages it brings to software development.

Please provide any other recommended inheritance interview questions that can reveal a candidate’s grasp of this key Java OOP concept. Additionally, please share any inheritance programming questions that evaluate a candidate’s hands-on coding abilities and mastery of methods overriding, abstract classes, and superclass/subclass creation.

If you found this article helpful or have suggestions to enhance its content, please leave a comment below. Your feedback is valuable; together, we can strive for excellence in Java programming proficiency. Best of luck in your endeavors, and may your Java interviews be challenging and rewarding!

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