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Top 15 Java OOPS Interview Questions for 2022

1) What are the advantages of Java Package?

Advantages of Java package are:
  • Provides access protection
  • Removes naming collision
  • Easily maintained

2) What are the types of Access Modifiers in Java?

Two types of Access Modifiers in Java are: 1) access modifiers
  • private
  • default
  • protected
  • public
2) non-access modifiers
  • static
  • abstract
  • synchronized
  • native
  • volatile
  • transient etc

3) What are the types of constructors in Java?

Two types of constructors in java are :
  • Default constructor
  • Parameterized constructor

4) What is the difference between constructor and method in Java?

Differnce between constructor and method :
Constructor Method
It is used to initialize the state of an object It is used to expose behaviour of an object
Invoked implicitly Invoked explicitly
Must not have return type Must have return type
It's name must be same as the class name. It's name may or may not be same as class name.

5) What are the different oops concept in Java?

The different oops concepts are :
  • Polymorphism
  • Inheritance
  • Encapsulation
  • Abstraction
  • Composition
  • Association
  • Aggregation

6) What are the restrictions of static method in Java?

Two main restrictions of static method are:
  • It can't use non static data member
  • super and this can't be used in static context

7) What will be the output of following piece of code?

class TutorialExam  
{    
int b=98;   
public static void main(String args[])  
{    
System.out.println(b);    
}    
}
OUTPUT:
Compile Time Error

8) Can we override java main method?

We can't override main method in java because main method is static.

9) Write a program in java for Single inheritance ?

Example of Single inheritance:
class Mom{    
void eat()  
{  
System.out.println("eating...");  
}    
}    
class Baby extends Mom  
{    
void run()  
{  
System.out.println("Running...");  
}    
}    
class TutorialExam{    
public static void main(String args[]){    
Baby b=new Baby();    
b.run();    
b.eat();    
}  
}

10) What are the types of inheritance in Java?

There are five types of inheritance in java:
  • Single inheritance
  • Multilevel inheritance
  • Hierarchical inheritance
  • Multiple inheritance
  • Hybrid inheritance

11) Write a program in java of super keyword where super() is provided by the compiler implicitly?

Example:
class Cars  
{    
Cars()  
{  
System.out.println("Choose a car : BMW, AUDI, JAGUAR");  
}    
}    
class BMW extends Cars  
{    
BMW()  
{    
System.out.println("Selected car :BMW");    
}    
}    
class TestCars  
{    
public static void main(String args[])  
{    
BMW d=new BMW();    
}  
}

12) Write a program in java of Runtime polymorphism?

Example of Runtime Polymorphism:
class Car  
{    
void run()  
{  
System.out.println("Running");  
}    
}    
class Audi extends Car  
{    
void run()  
{  
System.out.println("Running with 150km/h");  
}    
public static void main(String args[])  
{    
Car c = new Audi();    
c.run();    
}    
}

13) What are the types of binding in Java?

Two types of binding in java are:
  • Static binding(early binding)
  • Dynamic binding(late binding)

14) What are the ways to achieve Abstraction in Java?

Two ways to achieve abstraction in java:
  • By using Abstract class
  • By using Interface

15) What are the commonly used methods of Object class in Java?

Commonly used methods of Object class in java are:
  • public int hashCode()
  • public String toString()
  • public final void notify()
  • public final void notifyAll()
  • public final Class getClass()
  • public boolean equals(Object obj)
  • protected void finalize()throws Throwable
  • public final void wait()throws InterruptedException
  • protected Object clone() throws CloneNotSupportedException
  • public final void wait(long timeout)throws InterruptedException
  • public final void wait(long timeout, int nanos)throws InterruptedException



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