Part 6
Java interview questions and answers on oops covered in this post:
Can I declare a final and abstract method in abstract class?
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You cannot declare final and abstract at a time. Either final
or abstract method can be declared.
-
You can declare the final method or abstract method inside
the abstract class individually.
Can we declare a class as Abstract without having a single abstract
method?
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You can declare an abstract class without a single abstract
method declared inside an abstract class.
-
Make a note if you declared the already abstract method then
it is mandatory to declare the class as abstract class.
 
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What is the difference between the final method and the abstract
method?
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Final method cannot override.
-
Abstract method must override in its implementation
class.
What is the difference between Interface and Abstract Class? Can you tell me one real-time example where Interface and abstract class implementation is the best practice?
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Abstract Class |
Interface |
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1. |
Abstract class must be declared with abstract keyword. |
An interface can be declared with the Interface keyword. |
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2. |
An abstract class can have constructors. |
An interface cannot have constructors. |
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3. |
An abstract class can have a concrete method and an abstract
method. |
An interface can have only an abstract method. You cannot have a
concrete method inside the interface. |
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4. |
An abstract class can be declared private, protected, default and
public methods. |
An interface can declare only public methods. |
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5. |
An abstract class can be declared private, protected and public
variables. |
An interface can declare only public variables. |
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6. |
An Abstract class can declare non-final and local variables. |
An interface can declare only final variables but not a local
variable. |
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7. |
An Abstract class can extend one class and implements multiple
interfaces. |
An interface can extend one or more interfaces only. |
|
8. |
An abstract class is a best practice when you have partial
implementation and the rest of the implementation is remaining. |
The interface is a best practice when there is no implementation at
all. |
Will the code compile if I have declared a single abstract method in class but doesn't declare the class as an abstract class?
-
No. Your class won’t compile you will get a compile-time
error.
-
If you have declared already an abstract method inside a
class then it is mandatory to declare that class as an abstract class.
Can we declare static method and static variables in abstract
class?
-
Yes. You can declare static method and static variables
inside an abstract class.
Can we declare the concrete method in abstract class?
-
Definitely, we can declare a concrete method inside an
abstract class.
-
Abstract class can have abstract methods as well as concrete
methods.
Can we use static members inside the non-static area?
-
Yes. We can use static members inside the non-static
area.
-
We can observe this in the following demo.
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package simplifiedjava.crackedInterview;
public
class
Parent { static int a = 10;
public
static
void
main(String[] args) {
new
Parent().check(); }
public
void
check(){
System.out.println("Parent Class check() method = "+ a);
}
}
Output : Parent Class check() method = 10 |
What is static import?
-
Static import means we are importing static members from
another class.
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Once we import static members then we can use those members
without the class name.
-
Generally, we use static members with the class name but once
you import then there is no need to use the class name. You can directly
access those members.
Where the static variables are stored in java?
- The static variables were stored in the Perm-Gen space (also called the
method area).
- The static variables are stored in the Heap itself.
- Java 8 onwards the Perm-Gen Space has been removed and a new space named
Meta-Space is introduced which is not part of Heap memory anymore unlike the
previous Perm-Gen Space.
- Java interview questions and answers all MNC - Click here
- Basic core java interview questions and answers for freshers - Click here
- Core java interview questions for 3 years experience - Click here
- Core java interview questions and answers for 3-5 years exp - Click here
- Core java interview questions and Answers for 5 - 7 Years exp - Click here
- Basic Java Interview Questions and Answers - Click here
- Java interview questions and answers on oops - Click here
- Java interview questions and answers on Strings - Click here
- Java interview questions on exception handling - Click here
- Interview questions on multithreading in java for experienced - Click here
- Interview questions on serialization in java for experienced - Click here
- Interview questions on inner class in java for experienced - Click here
- Interview questions on Collections in java for experienced - Click here
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Thank you techies for visiting this blog. I hope you enjoyed this blog and got more technical knowledge. I have tried to cover all types of questions and provided examples tested on eclipse as much as I can. Guys, please don’t just mug up the questions and answers. Try to clear your concepts with examples. Try to write a code on eclipse once you read the concepts. It will help you to memorize the concepts for a very long time. Simultaneously you will be prepared for interview programs as well. It will help you to survive in the IT sector for a long time. It may be easy to crack an interview but it's really tough to survive in the IT industry with inadequate knowledge and skills. I have collected all the questions from actual interviews attended by my friends, colleagues, college mate and classmate. I have covered frequently asked questions as well as challenging questions. I have included many programs to understand the concept thoroughly. I will try to explain the concept with the help of a real-time program in eclipse. You can share more questions which are not covered in this blog or post. Always welcome your suggestions and queries. I will definitely try to resolve it. Please comment your queries and new set of questions under the comment sections. I will create a new post for those questions.
My total experience is 10. Initially I had worked on some support
projects and then I moved to java projects. I had worked with many
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Services, Cybage Softwares. Fortunately, TCS and Cybage
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