Core Java - Interview Questions and Answers for 'Core Java' | Search Interview Question

Interview Questions and Answers - Order By Rating

Q121. What are the biggest challenges for Java technology in the coming years?

Ans. JVM - With Cloud and Serverless, this could be a hurdle for it to be preferred technology.

Confusion between OOP and Functional Programming.

Slower speed of innovation due to wider adoption.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q122. Difference between List and ArrayList ?

Core Java

Ans. List is an interface whereas ArrayList is an implementation of List.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve list arraylist list vs arraylist difference between collections Asked in 2 Companies basic}

Q123. If you override hashcode to always return true, how a hash based collection will behave?

Core Java

Ans. At that bucket, it will form a linked list depending on what equals method evaluates for that object.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve hashcode collections Asked in 2 Companies}

Q124. Difference between String constant and String non-constant pools?

Core Java

^{This question was recently asked at 'VMWare'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q125. Difference between "extend" and "implement" in java?

Core Java

^{This question was recently asked at 'VM Ware'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q126. Can we serialize objects with only private variables in Java ?

Core Java

Ans. It depends on how we are serializing. The Serialization API doesn't worry about private variables and convert it into binary representation.

If we are using a library to map it to JSON / XML using XML Mappers, it may create trouble.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve serialization}

Q127. What is input Stream ?

Core Java

^{This question was recently asked at 'SQUAD Infotech'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve stream inout output inour stream Asked in 1 Companies}

Q128. What will happen if there are no collections in java ?

Core Java

Ans. Collections in Java is nothing but a library implementation for data structures and algorithm. If it's not available , we might have to include some other library or provide our own implementation.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve collections}

Q129. What will happen if there are no enums in Java ?

Core Java

Ans. Enums in Java is a facility to have objects upfront and use them as constants. Even if such a facility is not available , a workaround could be achieved.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve enum}

Q130. What will happen if there are no interfaces in Java ?

Core Java

Ans. Abstract classes can take care of that to a certain extent. Though they are little heavier than Interfaces but An abstract class with all abstract methods and no instance variables will be able to help with everything that currently an interface does.

The only problem is that a class can only extend one class whereas it can implements multiple interfaces and that is the reason Interfaces were introduced in Java, i.e to get over the problem of multiple inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve interfaces expert}

Q131. What are the different ways to create objects in Java ?

Core Java

Ans. 1. Using new operator
3. Using Class.forName or Reflection
4. Using clone
5. Using Deserialization

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q132. Can we create object in static block ?

Core Java

^{This question was recently asked at 'DXC Technologies'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q133. in the following class:
class A {
void methoda(Object o) {
Sysout("Object");
}

void methoda(String s) {
Sysout("String");
}

public static void main(String []args) {
A a = new A();
a.methoda(null);
}
}

what will be printed?

Core Java

Ans. String

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Code Coding method overloading Asked in 1 Companies}

Q134. How many read and write operations are provided at the same time by ConcurrentHashMaps ?

Core Java

Ans. ConcurrentHashMaps provide unlimited read operation fro multi threaded environment. For write operation only one thread can change value for particular segment of map.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve ConcurrentHashMap Asked in 1 Companies}

Q135. what is volatile and atomic

Core Java

Ans. When you declare a member/variable as volatile, you are forcing threads to read values from main memory instead of thread memory.

When you declare as atomic, the read and update/write operations are performed as a single unit. A lock is acquired during atomic operation.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 2 Companies}

Q136. serialization and deserialization of singleton class

Core Java

Ans. The problem with serialized singleton class is that whenever we deserialize it, it will create a new instance of the class. To overcome this scenario all we need to do is to provide the implementation of readResolve() method.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve singleton serialization Asked in 1 Companies}

Q137. Can a double value be cast to a byte ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q138. How do you convert List to Array ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q139. Explain briefly about Queue Interface ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve queue}

Q140. What is strictfp Modifier?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve strictfp}

Q141. What is the Main Advantage of the native Key Word?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve native keyword}

Q142. Why is Java platform independent ?

Core Java

Ans. Platform independent language means once compiled you can execute the program on any platform (OS). Java is platform independent. Because the Java compiler converts the source code to bytecode, which is Intermediate Language. Bytecode can be executed on any platform (OS) using JVM( Java Virtual Machine).

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q143. What is the difference between the 'A' and "A" in Java ?

Core Java

Ans. 'A' is a character whereas "A" is a String.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q144. Does Hashtable in Java use stack operation ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q145. Differences between class not found exception and noclassdef found error ?

Core Java

Ans. ClassNotFoundException is an exception that occurs when we try to load a class at run time using Class.forName() or loadClass() methods and mentioned classes are not found in the classpath.

NoClassDefFoundError is an error that occurs when a particular class is present at compile time, but was missing at run time.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve exception handling ClassNotFoundException NoClassDefFoundError Asked in 1 Companies}

Q146. Define Collection

Core Java

^{This question was recently asked at 'Amber Road'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q147. What is the use of final String when Strings are immutable ?

Core Java

^{This question was recently asked at 'Cyient'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve string Asked in 1 Companies}

Q148. How can we check class file format in java ?

Core Java

^{This question was recently asked at 'Jagan Institute of Management Studies (JIMS)'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q149. Why string pool concept has been introduced in string ?

Core Java

Ans. Memory Sharing and Optimal memory utilization.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve String Pool Asked in 1 Companies}

Q150. What will the following code print upon executing main method of Main class

public class BaseClass {

BaseClass(){
this(2);
System.out.println("Hello I am in Base Class Constructor");
}

BaseClass(int i){
System.out.println("Hello I am in Base Class int argument Constructor");
}
}

public class DerivedClass extends BaseClass{
DerivedClass(){
System.out.println("Hello I am in Derived Class Constructor");
}
}

public class Main {

public static void main(String[] args) {
DerivedClass derivedClass = new DerivedClass();
}
}

Core Java

Ans. Hello I am in Base Class int argument Constructor
Hello I am in Base Class Constructor
Hello I am in Derived Class Constructor

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve constructor}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.