Part 1
Core java interview questions and answers for 3-5 years experience covered in this post:
Will the code compile If the parent
class method is not throwing any exception but the child class method
is throwing an unchecked exception or Runtime Exception?
- Yes. Code will compile if parent class method is not throwing any
exception but child class method throws runtime exception or unchecked
exception.
|
package simplifiedjava.crackedInterview; public class OverrideOverloadedMethodDemo {
public static void
main(String[] args) {
Parent p
= new
Parent();
Child c
= new
Child();
c.check("Brother");
} } package simplifiedjava.crackedInterview; import java.io.IOException; public class Parent {
public void
check(String relation){
System.out.println("Parent Class check() method.");
} } package simplifiedjava.crackedInterview; public class Child extends Parent{
public void
check(String relation)throws
NullPointerException{
System.out.println("Child Class check() method.");
} }
Output : Child Class check() method. |
Can we have a constructor in abstract
class? If we can't instantiate abstract class then why there is a need
for a constructor in abstract class?
- Yes. We can declare a constructor inside the abstract
class.
- Absolutely right we cannot instantiate abstract class but when its Implementation class or child class instantiate that time abstract class constructor will be called.
 
Note: Please click on Image to Purchase the books from Amazon.in |
Can we declare a class inside a
class?
- Yes we can declare a class inside a class.
- For a demonstration please refer to the below
example.
|
package simplifiedjava.crackedInterview; public class ClassInsideClass {
class
Inner{
public void
greetings() {
System.out.println("Hello From Inner Class");
} }
public static void
main(String[] args) {
ClassInsideClass.Inner inner
= new
ClassInsideClass().new
Inner();
inner.greetings();
}
}
Output: Hello From Inner Class |
When the constructor will be executed
once you declare the constructor inside the enum?
- When constant enum values are passed to the constructor.
Can we create a custom exception
class? If yes then what are the steps to create a custom exception
class?
- Yes we can create a custom exception class.
- Please follow the following steps to create your custom
exception.
1. Create one Custom class and extends the Exception class.
2. Create one String type local variable and assign your custom message to
that variable.
3. Pass the custom message in the Custom class constructor while
instantiating the custom class.
4. Override toString() method to print the custom message.
5. We can simply throw a custom exception in any method and pass a custom
message while creating a custom object.
- Please refer to the below example to create a custom exception.
|
package simplifiedjava.crackedInterview; public class CustomException extends Exception { private String message;
public
CustomException(String message) {
this.message
= message; }
public
String toString() {
return message; }
public static void
main(String[] args) {
try {
if(args.length
>= -1) {
throw new
CustomException("No Argument Exception");
}
}catch(CustomException e) {
System.out.println(e);
}
}
}
Output: No Argument Exception |
What are the rules we must follow
while throwing an exception in an overridden method?
- If the superclass method does not declare an exception, the subclass’s
overridden method cannot declare the checked exception.
- If the superclass method does not declare an exception, the subclass’s
overridden method can declare an unchecked or runtime exception.
- If the superclass method declares an exception, the subclass’s overridden
method can declare the same exception or child class of that exception but
cannot declare the parent class of that exception.
- Please refer to the below examples for more clarity.
|
Parent Class Method |
Child Class Method |
Status |
|
Calculate() |
Calculate() throws IOException |
Not Allowed. Reason: If the parent class method doesn’t
throw any exception then the child class method should not through
any checked exception. You can throw unchecked exception.
|
|
Calculate() |
Calculate() throws NullPointerException |
Allowed. |
|
Calculate() throws IOException |
Calculate() |
Allowed. |
|
Calculate() throws NullPointerException |
Calculate() |
Allowed. |
|
Calculate() throws ArithmeticException |
Calculate()throws Exception |
Not Allowed. Reason: Child class method cannot throw
parent exception of Parent class. |
|
Calculate() throws Exception |
Calculate() throws Exception |
Allowed. |
What is Synchronization?
- Synchronization is a technique used in a multi-threading environment to control the access of shared resources on multiple threads.
- We can achieve thread-safety in multiple ways. Please refer to the below 8 options.
1. Synchronized Methods.
2. Synchronized Blocks.
3. Synchronized Collection. (Using Collections Utility
Class).
4. Concurrent Collection.
5. Immutable Implementation.
6. Thread-Local Field.
7. Volatile Field.
8. Stateless Implementation.
Explanation in details.
1.
Synchronized Methods:
Ø The method can be declared with a
synchronized
keyword.
Ø Once you declared the method with a
synchronized
keyword then only one thread can execute shared resources at a time.
Other threads will be blocked until the first thread finishes its
execution.
Ø synchronized
method depends on either “Intrinsic Lock” or “Monitor Lock”.
Ø When the thread calls the
synchronized
method, it acquires the intrinsic lock.
Ø The Monitor is just a reference to the role that the lock
performs on the associated objects.
Ø Please refer to the below example.
|
package simplifiedjava.crackedInterview; public class SynchronizedMethodDemo {
int
counter
= 0;
public
synchronized
void
getCounter() {
counter
=+ 1; // Similar to counter = counter +1;
System.out.println("Counter is "+ counter); }
public
static
void
main(String[] args) {
new
SynchronizedMethodDemo().getCounter();
}
} |
2.
Synchronized Block:
Ø A
synchronized
block can be called a statement block.
Ø Method synchronization is highly expensive so to avoid
this situation we can perform synchronization at the statement level
which is less expensive from a performance perspective.
Ø A
synchronized
block generally declares inside a method.
Ø Please refer to the below example.
|
package simplifiedjava.crackedInterview;
import
java.util.ArrayList;
import
java.util.Arrays;
import
java.util.Collection; import java.util.Collections; public class SynchronizedBlockDemo {
int
counter
= 0;
public
void
getCounter() {
synchronized(this) {
counter
=+ 1; // Similar to counter = counter +1;
}
System.out.println("Counter is "+ counter); }
public
static
void
main(String[] args) {
new
SynchronizedMethodDemo().getCounter();
}
} |
3.
Synchronized Collection:
Ø We can create a thread-safe collection by using utility
methods of the Collections utility class.
Ø Once you create the thread-safe collection object then
only one thread can execute at a time. While other threads will be
blocked until the collection object is unblocked by the first
thread.
Ø Please refer to the below example.
|
package simplifiedjava.crackedInterview;
import
java.util.Arrays;
import
java.util.Collections; import java.util.List; public class SynchronizedCollectionDemo {
public
static
void
main(String[] args) {
Thread t1
= new
Thread(new
MyClass1());
Thread t2
= new
Thread(new
MyClass2());
t1.start();
t2.start();
} } class MyClass1 implements Runnable{
@Override
public
void
run()
{
List<Integer> list1
= Arrays.asList(10,20,30,40,50);
List<Integer> synchronizedList1
= Collections.synchronizedList(list1);
for(Integer i
: list1) {
System.out.println(i);
}
} } class MyClass2 implements Runnable{
@Override
public
void
run() {
List<Integer> list2
= Arrays.asList(60,70,80,90,100);
List<Integer> synchronizedList2
= Collections.synchronizedList(list2);
for(Integer i
: list2) {
System.out.println(i);
}
}
} |
4.
Concurrent Collection:
Ø Java provides java.util.concurrent package for thread
safety.
Ø Java.util.concurrent package has some thread safe classes
like ConcurrentHashMap, CopyOnWriteArrayList, CopyOnWriteArraySet.
Ø Please refer to the below example.
|
package simplifiedjava.crackedInterview;
import
java.util.Map; import java.util.concurrent.ConcurrentHashMap; public class ConcurrentCollectionDemo {
public
static
void
main(String[] args) {
Map<String,Integer> concurrentMap
= new
ConcurrentHashMap<>();
concurrentMap.put("one", 1);
concurrentMap.put("two", 2);
concurrentMap.put("three", 3);
}
} |
5.
Immutable Implementation:
Ø Immutable means its internal states can’t be changed once
it is created.
Ø If we need to share the state between different threads,
we can create thread-safe classes by making them immutable classes.
Ø If the state will be fixed forever then immutable objects
can be used thread-safely.
Ø Please refer to the below example.
|
package simplifiedjava.crackedInterview; public final class ImmutableClassDemo { private final String empCode="E001";
public
String getEmpCode() {
return
empCode;
}
} |
6.
Thread-Local Field:
Ø We can easily create classes whose fields are
thread-local by simply defining private fields in the Thread class.
Ø We can create thread-safe classes that don’t share states
between threads by making their fields thread-local.
Ø Please refer to the below example.
|
package simplifiedjava.crackedInterview;
import
java.util.Arrays; import java.util.List; public class ThreadLocalDemo1 extends Thread { private final List<Integer> numList = Arrays.asList(10,20,30,40,50);
@Override
public
void
run() {
for(int
n
: numList) {
System.out.println(n);
}
} } package simplifiedjava.crackedInterview;
import
java.util.Arrays; import java.util.List; public class ThreadLocalDemo2 extends Thread{ private final List<String> wordList = Arrays.asList("Hi","Hello","GM","GA","GN");
@Override
public
void
run() {
for(String str
: wordList) {
System.out.println(str);
}
}
} |
7.
Volatile Field:
Ø If you declare a variable as volatile, JVM will store
those variables on main memory.
Ø We can make sure every time JVM reads the value from the
main memory.
Ø Every time JVM writes the value it will write on the main
memory.
Ø Volatile keyword ensures that variable will be visible to
all thread and thread can read the value from main memory.
Ø Please refer to the below example.
|
package simplifiedjava.crackedInterview; public class ThreadLocalVariableDemo {
private
volatile
int
empId; private String name; public static void main(String[] args) {
}
} |
8.
Stateless Implementation:
Ø Stateless implementation is the simplest way to achieve
thread safety.
Ø Stateless implementation is nothing but function
implementation which produces the same result every time. There is no
change to change the state by any thread.
Ø Please refer to the below example.
|
package simplifiedjava.crackedInterview; public class StateLessImplementationDemo { public static void main(String[] args) {
int
i
= 10;
int
square
= i
* i
;
System.out.println(square);
}
} |
What is the purpose of join()
method?
- Thread class provides the join() method which allows one thread to wait
until another thread completes its execution.
- If a thread wants to wait until completing some other thread then we
should go for the join(); method.
- In above example, Thread1.join(Thread2) and Thread2.join(Thread3) in the
above case Thread3 will execute first and then thread2 and then
thread1.
What are the methods used for
Serialization and Deserialization?
- For Serialization we have to use writeObject() method which
belongs to ObjectOutputStream.
- For Deserialization we have to use readObject() method which belongs to ObjectInputStream.
Can we declare outer class as a Default or Strictfp or Final?
- Yes, all three keywords are applicable to the outer class.
- 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
Upcoming questions in next post:
11. Can constructor have return type.
12. What's the difference between stackoverflowerror and outofmemoryerror in java
13. What happend when exception occured in thread.
14. What are the methods used for Externalization.
15. What is method local inner class.
16. How many .class files will be created if there are 2 inner classes inside outer class.
17. What is the difference between Collection and Collections.
18. What is Circular Queue.
19. What is Dictionary class?
20. Can you declare public static void main() method inside functional interface.
|
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
multi-national companies like R-Systems, Tata Consultancy
Services, Cybage Softwares. Fortunately, TCS and Cybage
has given me an opportunity to take interviews for experienced
candidates. I have conducted more than 1000 interviews by now. Mock sessions will be conducted for minimal charges. I will guide you personally on how to crack interviews. All sessions will be online sessions only. My interview book will be provided free of cost if you enroll for personal training. Once you have done practice then I assured you will definitely crack almost all java interviews. I have published my book named with "All MNC Java Interview" which is available on amazon. You can go through it or you can directly contact to me if you are interested to read the book. I will give you special discount. I have covered near about 550 questions and answers with program tested on eclipse and necessary diagram. I have covered interview questions asked in all reputed MNC like TCS, Infosys, Capgemini, Tech Mahindra, Cognizant, City Bank, Barclays, Amdocs, Mindtree etc. My purpose behind this book is, help you to get a job in your dream company. I can understand this is a struggling period for job seekers and freshers. Everybody must have gone from this phase. so never give up. Keep upgrading yourself. I am sure you will get a job in your dream company. All the best!!! Please reach out to me for personal training for interview preparation.
You can reach out to me at mncjavainterview@gmail.com.
|
0 Comments