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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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Q191. Can you write immutable class without final?

Ans. By making the constructor private

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Q192. Does Java SE has Immutable collections ?

Ans. Yes wef from Java 9

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Q193. Where to use interface and abstract class ?

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Q194. What are basic functions of OOPS ?

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Q195. Write a java program to find the maximum profit in day trading

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Q196. What is the biggest Design problem in Java ?

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

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Q197. What is TypeCasting ?

Ans. Assigning a value of one type to a variable of another type is known as Type Casting.

Example :

int x = 10;
byte y = (byte)x;

In Java, type casting is classified into two types, Widening Casting(Implicit) widening-type-conversion and Narrowing Casting (Explicitly done) narrowing-type-conversion.

Widening or Automatic type converion - Automatic Type casting take place when,the two types are compatible and the target type is larger than the source type

Example :

public class Test {
public static void main(String[] args) {
int i = 100;
long l = i; //no explicit type casting required
float f = l;//no explicit type casting required
System.out.println("Int value " i);
System.out.println("Long value " l);
System.out.println("Float value " f);
}
}

Narrowing or Explicit type conversion - When you are assigning a larger type value to a variable of smaller type, then you need to perform explicit type casting.

Example :

public class Test{
public static void main(String[] args) {
double d = 100.04;
long l = (long)d; //explicit type casting required
int i = (int)l;//explicit type casting required
System.out.println("Double value " d);
System.out.println("Long value " l);
System.out.println("Int value " i);
}
}

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Q198. Why doesn't this code give compile time error when we are clearly trying to add an integer element to an array of Strings

Object[] strArray = new String[2];
strArray[0] = 5;

Ans. Because the reference is of Object Array and the resolution of what it holds is identified at the runtime.

String[] strArray = new String[2];
strArray[0] = 5;

would have given the compile time array as the reference is of String array.

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Q199. Will this give compile time error ?

Object[] strArray = new String[2];
strArray[0] = 5;

Ans. No. But It will throw ArrayStoreException at runtime.

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Q200. What is the problem with this code

String[] strArray = new String[2];
strArray[0] = 5;

Ans. We are trying to add an integer element to an array of String. Will give compile time error.

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Q201. If arrays cannot be resized , Why is this code valid

String[] strArray = new String[2];
strArray = new String[5];

Ans. We are not resizing the first array here but assigning the reference strArray to a new Array with size 5.

So after line 2, We have 2 arrays in memory, one with size 2 and other with size 5 with strArray referring to second array with size 5.

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Q202. Is this code valid

String[] strArray = new String[2];
strArray.length = 5;

Ans. It will give compile time error saying "The final field array.length cannot be assigned"

Arrays once initialized cannot be resized.

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Q203. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[3]{"Buggy","Bread"};

Ans. No. It will result in error saying "Cannot define dimension expressions when an array initializer is provided"

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Q204. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[]{"Buggy","Bread"};

Ans. Yes, size of the array will be 2.

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Q205. Is this array declaration correct ? If not , Why ?

String[] strArray = new String[];

Ans. No, We haven't specified the size of array to be initialized.

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Q206. Which memory segment holds the byte code ?

Ans. Code Segment

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Q207. What is meant by "unreachable code" ? Can you write a code segment explaining this ?

Ans. Unreachable code is a code segment that can never be executed in any case. For example -

int x = 5;
return;
System.out.println(x);

In this code , 2nd line will return the control out of the method and hence 3rd line will never get executed and hence is unreachable code. This will be caught at compile time only.

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Q208. Can we call a static method using reference currently pointing to null.

Ans. yes, we can.
exa: public class Java{
public static void main(String... args) {
JAva j= null;
j.greeting(); // call with null reference
}
public static void greeting() {
System.out.println("Hello World");
}
} // output: Hello World

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Q209. How to run jar file using command prompt

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Q210. Diff between Runtime.getRunTime().gc() and System.gc()

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