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

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Q151. Can we serialize objects with only private variables in 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.

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Q152. What is input Stream ?

Core Java

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Q153. 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.

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Q154. 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.

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Q155. 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.

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Q156. 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

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Q157. Can we create object in static block ?

Core Java

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Q158. Explain servlet lifecycle

Java EE

Ans. Init -> service -> destroy.

Out of these, init and destroy are called once per servlet whereas service is called every time when a request is made to the servlet.

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Q159. 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

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Q160. 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.

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Q161. 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.

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Q162. 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.

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Q163. Can a double value be cast to a byte ?

Core Java

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Q164. How do you convert List to Array ?

Core Java

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Q165. Explain briefly about Queue Interface ?

Core Java

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Q166. What is strictfp Modifier?

Core Java

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Q167. What is the Main Advantage of the native Key Word?

Core Java

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Q168. What is doCallRealMethod() method used for ?

PowerMock

Ans. When we Mock an object and then make a reference to any method using mocked object reference , java never makes a call to that method and looks for mocked value to be returned or null if none specified. But If we want that to be overridden and want java to make actual method call upon using mocked object reference, this method can be used.

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Q169. What does the following code

MockitoAnnotations.initMocks(this);

Mockito

Ans. Initializes objects annotated with Mockito annotations

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Q170. 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).

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Q171. What is the difference between the 'A' and "A" in Java ?

Core Java

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

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Q172. What is the difference between bubble sort using Java and C++ ?

Programming Language

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Q173. Does Hashtable in Java use stack operation ?

Core Java

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Q174. 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.

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Q175. Define Collection

Core Java

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Q176. What is type script ? What are the advantages of typescript ? How is it different than javascript ?

TypeScript

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Q177. What is the use of final String when Strings are immutable ?

Core Java

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Q178. How can we check class file format in java ?

Core Java

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Q179. Why string pool concept has been introduced in string ?

Core Java

Ans. Memory Sharing and Optimal memory utilization.

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Q180. 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

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