Basic Java Interview Questions and Answers covered in this
post:
What is static import?
- Static import means we are importing static members from another class.
- Once we import static members then we can use those members without the
class name.
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.
 
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What is the diamond problem in Java? Why java doesn't support multiple inheritance?
- Diamond problem comes into the picture in multiple inheritance.
- When one class is inheriting the same property from multiple classes.
This is called the diamond problem.
- E.g. There are 3 classes. Class A, Class B and Class C. Class A and Class B have add() method and when class C extends class A and class B. Class C is trying to override add() method then which method compiler will refer for overriding. There is ambiguity. This is a diamond problem. That’s why java doesn’t support multiple inheritance.
What is a marker interface? Can you tell me the example of a marker interface?
- An empty interface is called a marker interface.
- Marker interface doesn’t have any method or variable.
- List of marker interfaces.
1. Serializable interface.
2. Cloneable interface.
3. Remote Interface.
What are the wrapper classes in java? Why do we require wrapper classes?
- Wrapper class is a class whose objects are wraps or contains primitive
data types.
- Wrapper class hold primitive values and is represented as an
object.
- All primitives has its own wrapper class.
- E.g. int has Integer, float has Float, double has Double etc.
- In the collection framework if we wanted to represent primitive as an object for manipulation then wrapper class can be used.
What is variable shadowing?
- Shadowing means a variable declared within a certain scope (Declared
inside method or block) has the same name as a variable declared in an
outer scope.
- In short, we have the same variable name in block or method and class
level variable.
- For a demonstration please refer to the below example.
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package simplifiedjava.crackedInterview; public class VariavleShadowingDemo { int num = 10;
public
void
printNum() {
int
num
= 20;
System.out.println("Num Value "+ num); }
public
static
void
main(String[] args) {
new
VariavleShadowingDemo().printNum();
}
}
Output : 20. Because local variable has highest priority inside
method. |
What is static method shadowing?
- The static method in the superclass will be hidden by the one that is
declared in the subclass. This mechanism is known as method shadowing.
- Method shadowing is applicable only for a static method.
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package simplifiedjava.crackedInterview; public class Parent {
public
static
void
printGreetings() {
System.out.println("Parent Class Static Method");
} } package simplifiedjava.crackedInterview; public class Child extends Parent{
public
static
void
printGreetings() {
System.out.println("Child Class Static Method"); }
public
static
void
main(String[] args) {
Parent.printGreetings();
Child.printGreetings();
}
}
Output:
Parent Class Static Method
Child Class Static Method |
What is object cloning?
- Object cloning means creating a duplicate copy of an
object.
- clone() can be used to creating the object clone.
What is a co-variant return type?
- Covariant return means that when one overrides a method, the return
type of the overriding method is allowed to be a subtype of the
overridden method's return type.
- In the below example, There are two classes Human and Men. Men class
extends the Human class.
- Both class has dressingStyle() method. This method is overriding in the
Men class. Both methods have the same return type but if you observe
then the parent class method returns the actual Human class object and
the child class method returns the Child class(Men Class) object when
the return type is Human. This is called covariant return type.
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package simplifiedjava.crackedInterview; public class Human {
public
Human dressingStyle() {
return
new
Human();
}
} package simplifiedjava.crackedInterview; public class Men extends Human {
public
Men dressingStyle() {
return
new
Men();
}
} |
What is the purpose of the final
keyword where it can be applicable?
- Final keyword can be applied to the following.
1. Variable: Final variable value cannot change once
assigned.
2. Method: Final method cannot override.
3. Class:
Final class cannot be sub-classed.
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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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