Core Java - Interview Questions and Answers for 'Inheritance' | Search Interview Question

Core Java - Interview Questions and Answers for 'Inheritance' - 26 question(s) found - Order By Newest

Frequently asked to fresh graduates and less experienced developers. Among the first few questions in many interviews.

Q1. What are the difference between composition and inheritance in Java?

Core Java

Ans. Composition - has-a relationship between objects.
Inheritance - is-a relationship between classes.

Composition - Composing object holds a reference to composed objects and hence relationship is loosely bound.
Inheritance - Derived object carries the base class definition in itself and hence its tightly bound.

Composition - Used in Dependency Injection
Inheritance - Used in Runtime Polymorphism

Composition - Single class objects can be composed within multiple classes.
Inheritance - Single class can only inherit 1 Class.

Composition - Its the relationship between objects.
Inheritance - Its the relationship between classes.

Sample Code for inheritance

Sample Code for composition

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java java concepts inheritance object oriented programming (oops) oops concepts composition object oriented programming (oops) oops concepts inheritance object oriented programming (oops) inheritance vs composition object oriented programming (oops) oops concepts Asked in 29 Companies basic frequent}

Try 5 Question(s) Test

Q2. Why every object constructor automatically call super() in Object before its own constructors?

Core Java

Ans. Derived object carries the body of its class as well as the body of the parent class. Its body ( member elements ) is initialized using its own class constructor whereas the body ( member elements ) carried from the parent class are initialized using super class constructor. So In order to initialize the elements of the parent class before its own elements are even initialized, super is called.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops constructor super inheritance object oriented programming (oops) oops concepts inheritence Asked in 1 Companies intermediate}

Q3. How compiler handles the exceptions in overriding ?

Core Java

Ans. 1)The overriding methods can throw any runtime Exception , here in the case of runtime exception overriding method (subclass method) should not worry about exception being thrown by superclass method.

2)If superclass method does not throw any exception then while overriding, the subclass method can not throw any new checked exception but it can throw any runtime exception

3) Different exceptions in java follow some hierarchy tree(inheritance). In this case , if superclass method throws any checked exception , then while overriding the method in subclass we can not throw any new checked exception or any checked exception which are higher in hierarchy than the exception thrown in superclass method

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java overriding exceptions inheritence inheritance object oriented programming (oops) oops concepts oops}

Frequently asked to fresh graduates and less experienced.

Q4. Difference between Composition and Inheritance ?

Core Java

Ans. Inheritance means a object inheriting reusable properties of the base class. Compositions means that an abject holds other objects.

In Inheritance there is only one object in memory ( derived object ) whereas in Composition , parent object holds references of all composed objects.

From Design perspective - Inheritance is "is a" relationship among objects whereas Composition is "has a" relationship among objects.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops oops concepts inheritance object oriented programming (oops) oops concepts composition object oriented programming (oops) oops concepts difference between basic interview question Asked in 12 Companies basic frequent}

Try 2 Question(s) Test

Frequently asked to fresh graduates and less experienced.

Q5. Which of the following is tightly bound ? Inheritance or Composition ?

Core Java

Ans. Inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts java oops composition object oriented programming (oops) oops concepts Asked in 1 Companies basic frequent}

Q6. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.

Core Java

Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve multiple inheritance object oriented programming (oops) oops concepts diamond problem Asked in 20 Companies basic frequent}

Q7. Does a class inherit the constructor of its super class?

Ans. No.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops constructor inheritence constructor inheritance yes no}

Q8. Can we compose the Parent Class object like this ?

class BuggyBread1 extends BuggyBread2 {

private BuggyBread2 buggybread2;

public static void main(String[] args){
buggybread2 = new BuggyBread2();
}
}

Ans. Yes.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java composition inheritance yesno}

Try 1 Question(s) Test

Q9. Can we have multiple inheritance in java using abstract class ?

Core Java

Ans. No

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve abstract class multiple inheritance object oriented programming (oops) oops concepts Asked in 2 Companies}

Q10. Does use of Final class enforces composition over Inheritance in Java ?

Core Java

Ans. Yes, to a certain extent. But the objective for Final class could be beyond just enforcing composition as certain classes might have been created without inheritance or composition in mind.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve final class composition object oriented programming (oops) oops concepts inheritance object oriented programming (oops) oops concepts composition object oriented programming (oops) oops concepts vs inheritance object oriented programming (oops) oops concepts expert}

Q11. What could be the reasons for restricting inheritance using final class ?

Core Java

Ans. 1. Enforcing composition over inheritance
2. Restricting overriding of certain methods
3. Final methods are faster than regular instance methods
4. Enforcing Immutability

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve final class reasons for final class restricting inheritance object oriented programming (oops) oops concepts expert}

Q12. What will happen if class implement two interface having common method?

Ans. That would not be a problem as both are specifying the contract that implement class has to follow.
If class C implement interface A & interface B then Class C thing I need to implement print() because of interface A then again Class think I need to implement print() again because of interface B, it sees that there is already a method called test() implemented so it's satisfied.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops interfaces multiple inheritance}

Q13. What are the different types of inheritance in Hibernate ?

Hibernate

Ans. Table Per Class , Table per Sub Class , Table per Concrete Class

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve hibernate orm inheritance hibernate Asked in 1 Companies Basic frequent}

Q14. Can we extend an Enum ?

Core Java

Ans. No. Enums are final by design.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java enums inheritance object oriented programming (oops) oops concepts yes-no Asked in 1 Companies intermediate}

Q15. Shouldn't we make a class with all static members is its just expected to be executed as a standalone program with just one thread. Moreover Lets assume that there is no runtime Polymorphism required and there is no need for serialization ?

Design

Ans. Still No in case we are making use of inheritance. we may have problem wherein we have program flow moving across common inherited method and specific methods of the derived class. call made to another static method in the parent class will only access the static class of the Parent class irrespective of the call from any of the derived class.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve static class static vs singleton inheritance}

Must know at all levels. Among Top 10 frequently asked questions in Java. Very frequently asked to fresh graduates or less experienced professionals.

Q16. What is Inheritance ?

Core Java

Ans. Its a facility for code reuse and independent extension wherein a derived class inherits the properties of parent class.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts oops concepts java concepts code reuse code re-use classes derived classes Asked in 14 Companies basic frequent}

Q17. How is multiple inheritance implemented in Java ?

Core Java

Ans. There was no multiple inheritance in java before version 8 as implementing multiple interfaces cannot be termed as inheritance.

With Java 8 , came the concept of default methods wherein the class implementing the interface carries the default implementation from the interface and hence facilitating multiple inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve multiple inheritance object oriented programming (oops) oops concepts inheritance object oriented programming (oops) oops concepts oops concept Asked in 10 Companies frequent}

Q18. What is multilevel inheritance ?

Core Java

Ans. Multi Level Inheritance is multi level hierarchy of classes. Here is the example - http://www.buggybread.com/2015/09/java-se-class-diagram-classes-that_603.html

Class RoleList extends ArrayList which in turn extends AbstractList which in turn extends AbstractCollection.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve multilevel inheritance object oriented programming (oops) oops concepts inheritance object oriented programming (oops) oops concepts oops concepts Asked in 3 Companies basic}

Try 1 Question(s) Test

Q19. Does default methods introduce multiple inheritance and the Diamond problem in Java 8 ?

Core Java

Ans. Default methods results in multiple inheritance of behavior and not of state. In case we try to implement multiple interfaces with default method having same name and signature, and don't override it in implementation class, it will throw an error.

For example -

interface MyInterface {
public void default myMethod(){
}
}

interface MyInterface2 {
public void default myMethod(){
}
}

class MyClass implements MyInterface,MyInterface2 {
}

This code will compilation error "Duplicate Default Method"

if we specify the definition of myMethod() in myClass, compiler won't complain and there is no conflict and MyClass can use overridden definition. But if we don't override myMethod() in MyClass, Java would be in conflict as to what definition should be carried to MyClass and hence throws compilation error.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve default methods java 8 multiple inheritance object oriented programming (oops) oops concepts diamond problem interfaces}

Q20. Can we access private members of the parent class ? i.e Are private members of the class visible in the derived class ?

Core Java

Ans. No, If both Parent and Derived are outer classes.

public class Vehicle {
private static String manufacturingDate = "2016";
}

public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // error - The field Vehicle.manufacturingDate is not visible
}
}

Yes, If derived is the inner class of Parent.

public class Vehicle {
private static String manufacturingDate = "2016";
static public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // no problem
}
}
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve private members private methods private variables inheritance object oriented programming (oops) oops concepts members visibility inner classes nexted classes basic frequent}

Q21. Difference between multiple and multi level inheritance ?

Core Java

Ans. Multiple Inheritance refers to the concept of a class inheriting multiple classes. Example - Class C extends Class A ,Class B. This is not allowed in Java.

Multilevel Inheritance refers to the concept of Inheritance in a chain. Example - Class B extends Class A, Class C extends Class B. This is permitted in Java.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts multiple inheritance object oriented programming (oops) oops concepts multi level inheritance object oriented programming (oops) oops concepts Basic frequent}

Q22. How are the concept of Association related to Composition and Inheritance ?

Core Java

Ans. Composition and Inheritance are the different types of Associations for Classes.

Composition is a has-a association between classes.
Inheritance is a is-a association between classes.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve composition object oriented programming (oops) oops concepts inheritance object oriented programming (oops) oops concepts association relationship between objects}

Q23. What happens to private variables during inheritance ?

Core Java

Ans. Private variables are not inherited. They are simply ignored and not made part of the derived object body.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve private variables inheritance object oriented programming (oops) oops concepts}

Q24. Explain Inheritance and Polymorphism.

Core Java

Ans. Getting parent class object properties into child class is called Inheritance.

The process of representing one form into multiple forms is called polymorphism.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts polymorphism object oriented programming (oops) oops concepts Asked in 1 Companies Basic frequent}

Q25. Is Runtime Polymorphism possible without Inheritance ?

Core Java

Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve runtime polymorphism object oriented programming (oops) oops concepts method overriding inheritance object oriented programming (oops) oops concepts}

Q26. Can a class extend itself in Java ?

Core Java

Ans. No

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts}

Q27. if classes B and C extends Class A, Which of the following initialization is correct ?

Core Java

a. B b = new C();

b. C c = new B();

c. B b = new A();

d. A a = new B();

Ans.d. A a = new B();

Q28. If class A implements X interface, and Class B implements Y interface, and X is the parent of Y, Which of the following initialization is correct ?

Core Java

a. A a = new B();

b. Y y = new A();

c. X x = new B();

d. Y y = new A();

Ans.c. X x = new B();

Q29. What is the relationship between Vehicle and Engine in this example ?

public class Vehicle {
   Enginer engine;
   public void move(){
      engine = new Engine();
      engine.start();
   }
}

Core Java

a. Composition ( Vehicle has a Engine )

b. Composition ( Engine has a Vehicle )

c. Inheritance ( Vehicle is a Engine )

d. Inheritance ( Engine is a Vehicle )

Ans.a. Composition ( Vehicle has a Engine )

Q30. What is the relationship between Car and Vehicle in the following code ?

public class Car extends Vehicle{
   Engine engine;

   public static void main(String[] args){
      Vehicle vehicle = new Car();
      car.move();
   }

   public void move(){
      engine = new Engine();
      engine.start();
   }
}

Core Java

a. Composition ( Vehicle has a Car )

b. Composition ( Car has a Vehicle )

c. Inheritance ( Vehicle is a Car )

d. Inheritance ( Car is a Vehicle )

Ans.d. Inheritance ( Car is a Vehicle )

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.