Part 2
Basic core java interview questions and answers for freshers covered in this post:
What is the difference between method
and constructor?
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Method |
Constructor |
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1. |
The method is used to implement the logic. |
Constructor is used to initializing the object. |
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2. |
The method can have a return type. |
A constructor cannot have a return type. |
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3. |
Method name can be anything or can be class name as well. |
The constructor name must be the same as the class name. |
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4. |
The method must invoke explicitly. |
A constructor can invoke automatically. |
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5. |
If you don’t have any method then the compiler won’t provide any
kind of method like a constructor. |
If you don’t have any constructor then the compiler will provide a
default constructor. |
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6. |
The method can be overridden or overloaded. |
The constructor can be overloaded but cannot overridden. |
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. |
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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.
 
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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 are the exceptions?
- Exception is an event, can be occurred during the execution of the program
that disrupts the normal flow of the program.
- You can say an Exception is an abnormal event that can be occurred during
the execution of the program.
- Exception can stop the execution of the program if not handled.
Which is the parent class of the
Exception hierarchy?
- Parent Class of Exception is Throwable.
What is deserialization?
- Deserialization is the reverse process of serialization.
- The reverse process of creating the object from a stored sequence of
bytes.
- Please refer to the above example for deserialization.
What are the characteristics of List
Interface?
- List is a child interface of the Collection interface.
- Duplicates are allowed.
- Insertion order preserved via index.
- Index is used to retrieve elements.
- Auto growable array.
What are the characteristics of Map
Interface?
- Map represents the group of objects as a key-value pair.
- Map is not a child interface of the Collection interface.
- Both keys and values are objects only.
- Characteristics of the map are as follows.
1. Underlying data structure is Hashtable.
2. Insertion order is not preserved.
3. Insertion order is based on Hashcode keys.
4. Duplicates keys are not allowed.
5. Values can be duplicated.
6. Heterogeneous (Different types of Object) objects are allowed
for both keys and values.
7. Null is allowed for keys only once.
8. Null is allowed for values multiple times.
9. Hashmap is Serializable because Hashmap implements a Serializable
interface.
10. Hashmap is Clonable because Hashmap implements a Clonable
interface.
11. Hashmap has not implemented RandomAccess.
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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.
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