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Q161. what is volatile and atomic

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

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 ?

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Q164. How do you convert List to Array ?

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Q165. Explain briefly about Queue Interface ?

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Q166. What is strictfp Modifier?

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

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Q168. What is doCallRealMethod() method used for ?

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);

Ans. Initializes objects annotated with Mockito annotations

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Q170. Why is Java platform independent ?

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 ?

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 ?

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Q174. Differences between class not found exception and noclassdef found error ?

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

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

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

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

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

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();
}
}

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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Q181. 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(){
super(1);
System.out.println("Hello I am in Derived Class Constructor");
}
}

public class Main {

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

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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Q182. Why line 4 in this code gives error saying "Cannot be referenced from a static context" ?

public class OuterClass {

public static void main(String[] args){
InnerClass innerClass = new InnerClass();
}

class InnerClass {

}
}

Ans. InnerClass is a non static inner class and hence can only be instantiated using instance of the outer class.

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Q183. What will the following code print upon executing main method of Main class ?

public class BaseClass {
BaseClass(int x){
System.out.println("Hello I am in Base Class Constructor");
}
}

public class DerivedClass extends BaseClass{
DerivedClass(){
super(1);
System.out.println("Hello I am in Derived Class Constructor");
}
}

public class Main {

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

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

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Q184. What will the following code print upon executing main method of Main class ?

public class BaseClass {
BaseClass(int x){
System.out.println("Hello I am in Base Class 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();
}
}

Ans. Compilation error as there is no default constructor available in BaseClass.

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Q185. What will the following code print upon executing main method of Main class ?

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

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

super();
}
}

public class Main {

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

Ans. There will be compilation error within constructor of Derived Class as "super must be the first statement in constructor body".

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Q186. What will the following print upon executing main method of Main class ?

public class BaseClass {
BaseClass(){
System.out.println("Hello I am in Base Class 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();
}
}

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

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Q187. Will it print the message in Base Class constructor if we execute main method of Main class ? why ?

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

public class DerivedClass extends BaseClass{
}

public class Main {

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

Ans. Yes.

When the Derived class constructor is initialized , a no argument super will be called intrinsically.

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Q188. Isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?

Ans. Both provide the thread safety but the actual difference come when talk about performance. CHM gives best performance when no of writer threads are less in number.

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Q189. Can we use try within catch block ?

Ans. Yes

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Q190. Is java fully platform independent ?

Ans. yes, Java is a class-based and object-oriented programming language. It is a platform-independent language i.e. the compiled code can be run on any java supporting platform. It runs on the logic of “Write once, run anywhere”.

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